CTOS

SEC source: 0001213900-22-018276 · ownership.xml · derivative · entry 2

NELSON GEORGIA R · CIK 0001141392 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 13,631 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

F2 · derivative.exercise_date: The restricted stock units vested in full on April 1, 2022.

F2 · derivative.expiration_date: The restricted stock units vested in full on April 1, 2022.

SEC source: 0001213900-22-018276 · ownership.xml · nonDerivative · entry 1

NELSON GEORGIA R · CIK 0001141392 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 38,631

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

SEC source: 0001213900-22-018278 · ownership.xml · derivative · entry 3

Rich Thomas R. · CIK 0001854514 · EVP- Rentals

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 150,000

Underlying: Common Stock · 50,000 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

F2 · derivative.exercise_date: The restricted stock units vest in four equal annual installments beginning on April 1, 2022.

F2 · derivative.expiration_date: The restricted stock units vest in four equal annual installments beginning on April 1, 2022.

SEC source: 0001213900-22-018278 · ownership.xml · nonDerivative · entry 2

Rich Thomas R. · CIK 0001854514 · EVP- Rentals

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 71,031

SEC source: 0001213900-22-018278 · ownership.xml · nonDerivative · entry 1

Rich Thomas R. · CIK 0001854514 · EVP- Rentals

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 85,857

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

SEC source: 0001213900-22-018266 · ownership.xml · derivative · entry 3

Carlsen James · CIK 0001854934 · CIO

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 26,250

Underlying: Common Stock · 8,750 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

F2 · derivative.exercise_date: The restricted stock units vest in four equal annual installments beginning on April 1, 2022.

F2 · derivative.expiration_date: The restricted stock units vest in four equal annual installments beginning on April 1, 2022.

SEC source: 0001213900-22-018266 · ownership.xml · nonDerivative · entry 2

Carlsen James · CIK 0001854934 · CIO

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 48,128

SEC source: 0001213900-22-018266 · ownership.xml · nonDerivative · entry 1

Carlsen James · CIK 0001854934 · CIO

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 50,724

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

SEC source: 0001213900-22-018270 · ownership.xml · derivative · entry 3

Haubenreich Adam G. · CIK 0001852510 · VP and General Counsel

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 93,750

Underlying: Common Stock · 31,250 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

F2 · derivative.exercise_date: The restricted stock units vest in four equal annual installments beginning on April 1, 2022.

F2 · derivative.expiration_date: The restricted stock units vest in four equal annual installments beginning on April 1, 2022.

SEC source: 0001213900-22-018270 · ownership.xml · nonDerivative · entry 2

Haubenreich Adam G. · CIK 0001852510 · VP and General Counsel

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 84,302

SEC source: 0001213900-22-018270 · ownership.xml · nonDerivative · entry 1

Haubenreich Adam G. · CIK 0001852510 · VP and General Counsel

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 93,568

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

SEC source: 0001213900-22-018281 · ownership.xml · derivative · entry 4

Ross Joe P. · CIK 0001852519 · President - Sales

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 150,000

Underlying: Common Stock · 50,000 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

F2 · derivative.exercise_date: The restricted stock units vest in four equal annual installments beginning on April 1, 2022.

F2 · derivative.expiration_date: The restricted stock units vest in four equal annual installments beginning on April 1, 2022.

SEC source: 0001213900-22-018281 · ownership.xml · nonDerivative · entry 2

Ross Joe P. · CIK 0001852519 · President - Sales

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 36,500

SEC source: 0001213900-22-018281 · ownership.xml · nonDerivative · entry 1

Ross Joe P. · CIK 0001852519 · President - Sales

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 51,326

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

SEC source: 0001213900-22-018274 · ownership.xml · derivative · entry 3

Meader Brad · CIK 0001852169 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 112,500

Underlying: Common Stock · 37,500 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

F2 · derivative.exercise_date: The restricted stock units vest in four equal annual installments beginning on April 1, 2022.

F2 · derivative.expiration_date: The restricted stock units vest in four equal annual installments beginning on April 1, 2022.

SEC source: 0001213900-22-018274 · ownership.xml · nonDerivative · entry 2

Meader Brad · CIK 0001852169 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 75,336

SEC source: 0001213900-22-018274 · ownership.xml · nonDerivative · entry 1

Meader Brad · CIK 0001852169 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 86,456

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

SEC source: 0001213900-22-018279 · ownership.xml · derivative · entry 4

Ross Fredrick M. Jr. · CIK 0001851369 · Director · Chief Executive Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 262,500

Underlying: Common Stock · 87,500 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

F2 · derivative.exercise_date: The restricted stock units vest in four equal annual installments beginning on April 1, 2022.

F2 · derivative.expiration_date: The restricted stock units vest in four equal annual installments beginning on April 1, 2022.

SEC source: 0001213900-22-018279 · ownership.xml · nonDerivative · entry 2

Ross Fredrick M. Jr. · CIK 0001851369 · Director · Chief Executive Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 59,898

SEC source: 0001213900-22-018279 · ownership.xml · nonDerivative · entry 1

Ross Fredrick M. Jr. · CIK 0001851369 · Director · Chief Executive Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 87,500

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

SEC source: 0001213900-22-018291 · ownership.xml · derivative · entry 6

ECP ControlCo, LLC · CIK 0001707921 · Director · 10% owner

ECP Management GP, LLC · CIK 0001815147 · Director · 10% owner

Energy Capital Partners Management, LP · CIK 0001815150 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 13,631 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F3 · derivative.exercise_price: Represents securities held directly by 21,238,988 shares held by NESCO Holdings, LP and 4,500,000 shares held by ECP Cardinal Holdings, LP

F6 · derivative.exercise_date: The restricted stock units vested in full on April 1, 2022.

F6 · derivative.expiration_date: The restricted stock units vested in full on April 1, 2022.

F1 · ownership.nature: Represents securities held directly by Energy Capital Partners Management, LP ("ECP Management"). ECP Management GP, LLC is the general partner of ECP Management and may be deemed to share beneficial ownership of the securities held by ECP Management.

F5 · ownership.nature: ECP ControlCo, LLC ("ECP ControlCo") is the managing member of ECP III GP LLC and the sole member of ECP Management GP, LLC. As a result, ECP ControlCo may be deemed to share beneficial ownership of the securities beneficially owned by ECP III GP LLC and ECP Management GP, LLC. The managing members of ECP ControlCo are Douglas Kimmelman, Andrew Singer, Peter Labbat, Tyler Reeder and Rahman D'Argenio all of whom collectively share the power to vote and dispose of the securities beneficially owned by ECP ControlCo. Each such individual disclaims beneficial ownership of such shares except to the extent of his pecuniary interest therein.

SEC source: 0001213900-22-018291 · ownership.xml · nonDerivative · entry 3

ECP ControlCo, LLC · CIK 0001707921 · Director · 10% owner

ECP Management GP, LLC · CIK 0001815147 · Director · 10% owner

Energy Capital Partners Management, LP · CIK 0001815150 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 120,779

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

F1 · ownership.nature: Represents securities held directly by Energy Capital Partners Management, LP ("ECP Management"). ECP Management GP, LLC is the general partner of ECP Management and may be deemed to share beneficial ownership of the securities held by ECP Management.

F5 · ownership.nature: ECP ControlCo, LLC ("ECP ControlCo") is the managing member of ECP III GP LLC and the sole member of ECP Management GP, LLC. As a result, ECP ControlCo may be deemed to share beneficial ownership of the securities beneficially owned by ECP III GP LLC and ECP Management GP, LLC. The managing members of ECP ControlCo are Douglas Kimmelman, Andrew Singer, Peter Labbat, Tyler Reeder and Rahman D'Argenio all of whom collectively share the power to vote and dispose of the securities beneficially owned by ECP ControlCo. Each such individual disclaims beneficial ownership of such shares except to the extent of his pecuniary interest therein.

SEC source: 0001213900-22-018285 · ownership.xml · derivative · entry 3

Heinberg Marshall · CIK 0001481338 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 24,537 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

F2 · derivative.exercise_date: The restricted stock units vested in full on April 1, 2022.

F2 · derivative.expiration_date: The restricted stock units vested in full on April 1, 2022.

SEC source: 0001213900-22-018285 · ownership.xml · nonDerivative · entry 1

Heinberg Marshall · CIK 0001481338 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 139,537

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

SEC source: 0001213900-22-018268 · ownership.xml · derivative · entry 3

EIN MARK · CIK 0001246840 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 13,631 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

F2 · derivative.exercise_date: The restricted stock units vested in full on April 1, 2022.

F2 · derivative.expiration_date: The restricted stock units vested in full on April 1, 2022.

SEC source: 0001213900-22-018268 · ownership.xml · nonDerivative · entry 1

EIN MARK · CIK 0001246840 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 1,013,631

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

SEC source: 0001213900-22-018283 · ownership.xml · derivative · entry 2

BADER PAUL · CIK 0001776138 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 13,631 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

F2 · derivative.exercise_date: The restricted stock units vested in full on April 1, 2022.

F2 · derivative.expiration_date: The restricted stock units vested in full on April 1, 2022.

SEC source: 0001213900-22-018283 · ownership.xml · nonDerivative · entry 1

BADER PAUL · CIK 0001776138 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 38,631

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

SEC source: 0001213900-22-018264 · ownership.xml · derivative · entry 3

BARRETT RAYMOND TODD · CIK 0001785100 · Chief Accounting Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 18,750

Underlying: Common Stock · 6,250 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

F2 · derivative.exercise_date: The restricted stock units vest in four equal annual installments beginning on April 1, 2022.

F2 · derivative.expiration_date: The restricted stock units vest in four equal annual installments beginning on April 1, 2022.

SEC source: 0001213900-22-018264 · ownership.xml · nonDerivative · entry 2

BARRETT RAYMOND TODD · CIK 0001785100 · Chief Accounting Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 4,403

SEC source: 0001213900-22-018264 · ownership.xml · nonDerivative · entry 1

BARRETT RAYMOND TODD · CIK 0001785100 · Chief Accounting Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 6,250

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

SEC source: 0001213900-22-026531 · ownership.xml · nonDerivative · entry 1

Ross Fredrick M. Jr. · CIK 0001851369 · Director · Chief Executive Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 60,680

F1 · shares: The Form 4 originally filed on behalf of the Reporting Person on April 5, 2022 inadvertently overstated the number of shares withheld by the Issuer in connection with the vesting event reported therein. This amendment is being filed to correct the number of shares withheld and the total number of shares directly held by the Reporting Person following such withholding.

F1 · balance_after: The Form 4 originally filed on behalf of the Reporting Person on April 5, 2022 inadvertently overstated the number of shares withheld by the Issuer in connection with the vesting event reported therein. This amendment is being filed to correct the number of shares withheld and the total number of shares directly held by the Reporting Person following such withholding.

SEC source: 0001213900-22-026528 · ownership.xml · nonDerivative · entry 1

Ross Fredrick M. Jr. · CIK 0001851369 · Director · Chief Executive Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 60,680

F1 · shares: The Form 4 originally filed on behalf of the Reporting Person on April 5, 2022 inadvertently overstated the number of shares withheld by the Issuer in connection with the vesting event reported therein. This amendment is being filed to correct the number of shares withheld and the total number of shares directly held by the Reporting Person following such withholding.

F1 · balance_after: The Form 4 originally filed on behalf of the Reporting Person on April 5, 2022 inadvertently overstated the number of shares withheld by the Issuer in connection with the vesting event reported therein. This amendment is being filed to correct the number of shares withheld and the total number of shares directly held by the Reporting Person following such withholding.

SEC source: 0001213900-23-027291 · ownership.xml · derivative · entry 10

BARRETT RAYMOND TODD · CIK 0001785100 · Chief Accounting Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 3,333

Underlying: Common Stock · 1,667 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

F4 · derivative.exercise_date: The restricted stock units vest in four equal, annual installments beginning on March 18, 2021.

F4 · derivative.expiration_date: The restricted stock units vest in four equal, annual installments beginning on March 18, 2021.

SEC source: 0001213900-23-027291 · ownership.xml · nonDerivative · entry 2

BARRETT RAYMOND TODD · CIK 0001785100 · Chief Accounting Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 12,737

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · shares: Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock.

SEC source: 0000899243-22-007080 · doc4.xml · nonDerivative · entry 7

Blackstone Energy Partners NQ L.P. · CIK 0001855931 · Former 10% Owner

BEP CTOS Holdings L.P. · CIK 0001857352 · Former 10% Owner

Blackstone Energy Family Investment Partnership SMD L.P. · CIK 0001851447 · Former 10% Owner

Blackstone Energy Family Investment Partnership NQ ESC L.P. · CIK 0001855942 · Former 10% Owner

Blackstone Capital Partners VI-NQ L.P. · CIK 0001855944 · Former 10% Owner

BCP CTOS Holdings L.P. · CIK 0001857351 · Former 10% Owner

Blackstone Family Investment Partnership VI-NQ ESC L.P. · CIK 0001856558 · Former 10% Owner

Blackstone Energy Management Associates NQ L.L.C. · CIK 0001855939 · Former 10% Owner

Blackstone EMA-NQ L.L.C. · CIK 0001855943 · Former 10% Owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

F1 · price: This amount represents the price per share of common stock, par value $0.0001 per share ("Common Stock"), of Custom Truck One Source, Inc. (the "Issuer") sold in a transaction exempt from registration pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended.

F8 · ownership.nature: Reflects shares of Common Stock directly held by Blackstone Family Investment Partnership VI-NQ ESC L.P. ("BE FIP").

F9 · ownership.nature: Blackstone Energy Management Associates NQ L.L.C. ("BEMA") is the general partner of BEP NQ and BEP CTOS. Blackstone EMA-NQ L.L.C. ("BEMA NQ") is the managing member of BEMA. BEP Side-by-Side GP NQ L.L.C. ("BEP GP") is the general partner of BE NQ. Blackstone Management Associates VI-NQ L.L.C. ("BMA NQ") is the general partner of BCP VI-NQ and BCP CTOS. BMA VI-NQ L.L.C. ("BMA VI-NQ") is the managing member of BMA NQ. Blackstone Family GP L.L.C. ("BS GP") is the general partner of BE SMD. BS GP is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. BCP VI-NQ Side-by-Side GP L.L.C. ("BCP GP") is the general partner of BE FIP.

F10 · ownership.nature: Blackstone Holdings III L.P. ("Holdings III") is the sole member of each of BEMA NQ, BEP GP and BMA VI-NQ. The general partner of Holdings III is Blackstone Holdings III GP L.P. ("Holdings III GP"). The general partner of Holdings III GP is Blackstone Holdings III GP Management L.L.C ("Holdings III GP Management"). Blackstone Holdings II L.P. ("Holdings II") is the sole member of BCP GP. Blackstone Holdings I/II GP L.L.C. ("Holdings I/II GP") is the general partner of Holdings II. Blackstone Inc. ("Blackstone") is the sole member of Holdings III GP Management and Holdings I/II GP. The sole holder of the Series II preferred stock of Blackstone is Blackstone Group Management L.L.C. ("BS Group Management"). BS Group Management is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman.

F11 · ownership.nature: Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person.

F12 · ownership.nature: Due to the limitations of the electronic filing system certain Reporting Persons are filing a separate Form 4.

F13 · ownership.nature: Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the securities reported herein for purposes of Section 16 of the Exchange Act or for any other purpose or that the Reporting Persons are subject to Section 16 of the Exchange Act.

SEC source: 0000899243-22-007080 · doc4.xml · nonDerivative · entry 6

Blackstone Energy Partners NQ L.P. · CIK 0001855931 · Former 10% Owner

BEP CTOS Holdings L.P. · CIK 0001857352 · Former 10% Owner

Blackstone Energy Family Investment Partnership SMD L.P. · CIK 0001851447 · Former 10% Owner

Blackstone Energy Family Investment Partnership NQ ESC L.P. · CIK 0001855942 · Former 10% Owner

Blackstone Capital Partners VI-NQ L.P. · CIK 0001855944 · Former 10% Owner

BCP CTOS Holdings L.P. · CIK 0001857351 · Former 10% Owner

Blackstone Family Investment Partnership VI-NQ ESC L.P. · CIK 0001856558 · Former 10% Owner

Blackstone Energy Management Associates NQ L.L.C. · CIK 0001855939 · Former 10% Owner

Blackstone EMA-NQ L.L.C. · CIK 0001855943 · Former 10% Owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

F1 · price: This amount represents the price per share of common stock, par value $0.0001 per share ("Common Stock"), of Custom Truck One Source, Inc. (the "Issuer") sold in a transaction exempt from registration pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended.

F7 · ownership.nature: Reflects shares of Common Stock directly held by BCP CTOS Holdings L.P. ("BCP CTOS").

F9 · ownership.nature: Blackstone Energy Management Associates NQ L.L.C. ("BEMA") is the general partner of BEP NQ and BEP CTOS. Blackstone EMA-NQ L.L.C. ("BEMA NQ") is the managing member of BEMA. BEP Side-by-Side GP NQ L.L.C. ("BEP GP") is the general partner of BE NQ. Blackstone Management Associates VI-NQ L.L.C. ("BMA NQ") is the general partner of BCP VI-NQ and BCP CTOS. BMA VI-NQ L.L.C. ("BMA VI-NQ") is the managing member of BMA NQ. Blackstone Family GP L.L.C. ("BS GP") is the general partner of BE SMD. BS GP is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. BCP VI-NQ Side-by-Side GP L.L.C. ("BCP GP") is the general partner of BE FIP.

F10 · ownership.nature: Blackstone Holdings III L.P. ("Holdings III") is the sole member of each of BEMA NQ, BEP GP and BMA VI-NQ. The general partner of Holdings III is Blackstone Holdings III GP L.P. ("Holdings III GP"). The general partner of Holdings III GP is Blackstone Holdings III GP Management L.L.C ("Holdings III GP Management"). Blackstone Holdings II L.P. ("Holdings II") is the sole member of BCP GP. Blackstone Holdings I/II GP L.L.C. ("Holdings I/II GP") is the general partner of Holdings II. Blackstone Inc. ("Blackstone") is the sole member of Holdings III GP Management and Holdings I/II GP. The sole holder of the Series II preferred stock of Blackstone is Blackstone Group Management L.L.C. ("BS Group Management"). BS Group Management is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman.

F11 · ownership.nature: Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person.

F12 · ownership.nature: Due to the limitations of the electronic filing system certain Reporting Persons are filing a separate Form 4.

F13 · ownership.nature: Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the securities reported herein for purposes of Section 16 of the Exchange Act or for any other purpose or that the Reporting Persons are subject to Section 16 of the Exchange Act.

SEC source: 0000899243-22-007080 · doc4.xml · nonDerivative · entry 5

Blackstone Energy Partners NQ L.P. · CIK 0001855931 · Former 10% Owner

BEP CTOS Holdings L.P. · CIK 0001857352 · Former 10% Owner

Blackstone Energy Family Investment Partnership SMD L.P. · CIK 0001851447 · Former 10% Owner

Blackstone Energy Family Investment Partnership NQ ESC L.P. · CIK 0001855942 · Former 10% Owner

Blackstone Capital Partners VI-NQ L.P. · CIK 0001855944 · Former 10% Owner

BCP CTOS Holdings L.P. · CIK 0001857351 · Former 10% Owner

Blackstone Family Investment Partnership VI-NQ ESC L.P. · CIK 0001856558 · Former 10% Owner

Blackstone Energy Management Associates NQ L.L.C. · CIK 0001855939 · Former 10% Owner

Blackstone EMA-NQ L.L.C. · CIK 0001855943 · Former 10% Owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

F1 · price: This amount represents the price per share of common stock, par value $0.0001 per share ("Common Stock"), of Custom Truck One Source, Inc. (the "Issuer") sold in a transaction exempt from registration pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended.

F6 · ownership.nature: Reflects shares of Common Stock directly held by Blackstone Capital Partners VI-NQ L.P. ("BCP VI-NQ").

F9 · ownership.nature: Blackstone Energy Management Associates NQ L.L.C. ("BEMA") is the general partner of BEP NQ and BEP CTOS. Blackstone EMA-NQ L.L.C. ("BEMA NQ") is the managing member of BEMA. BEP Side-by-Side GP NQ L.L.C. ("BEP GP") is the general partner of BE NQ. Blackstone Management Associates VI-NQ L.L.C. ("BMA NQ") is the general partner of BCP VI-NQ and BCP CTOS. BMA VI-NQ L.L.C. ("BMA VI-NQ") is the managing member of BMA NQ. Blackstone Family GP L.L.C. ("BS GP") is the general partner of BE SMD. BS GP is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. BCP VI-NQ Side-by-Side GP L.L.C. ("BCP GP") is the general partner of BE FIP.

F10 · ownership.nature: Blackstone Holdings III L.P. ("Holdings III") is the sole member of each of BEMA NQ, BEP GP and BMA VI-NQ. The general partner of Holdings III is Blackstone Holdings III GP L.P. ("Holdings III GP"). The general partner of Holdings III GP is Blackstone Holdings III GP Management L.L.C ("Holdings III GP Management"). Blackstone Holdings II L.P. ("Holdings II") is the sole member of BCP GP. Blackstone Holdings I/II GP L.L.C. ("Holdings I/II GP") is the general partner of Holdings II. Blackstone Inc. ("Blackstone") is the sole member of Holdings III GP Management and Holdings I/II GP. The sole holder of the Series II preferred stock of Blackstone is Blackstone Group Management L.L.C. ("BS Group Management"). BS Group Management is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman.

F11 · ownership.nature: Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person.

F12 · ownership.nature: Due to the limitations of the electronic filing system certain Reporting Persons are filing a separate Form 4.

F13 · ownership.nature: Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the securities reported herein for purposes of Section 16 of the Exchange Act or for any other purpose or that the Reporting Persons are subject to Section 16 of the Exchange Act.

SEC source: 0000899243-22-007080 · doc4.xml · nonDerivative · entry 4

Blackstone Energy Partners NQ L.P. · CIK 0001855931 · Former 10% Owner

BEP CTOS Holdings L.P. · CIK 0001857352 · Former 10% Owner

Blackstone Energy Family Investment Partnership SMD L.P. · CIK 0001851447 · Former 10% Owner

Blackstone Energy Family Investment Partnership NQ ESC L.P. · CIK 0001855942 · Former 10% Owner

Blackstone Capital Partners VI-NQ L.P. · CIK 0001855944 · Former 10% Owner

BCP CTOS Holdings L.P. · CIK 0001857351 · Former 10% Owner

Blackstone Family Investment Partnership VI-NQ ESC L.P. · CIK 0001856558 · Former 10% Owner

Blackstone Energy Management Associates NQ L.L.C. · CIK 0001855939 · Former 10% Owner

Blackstone EMA-NQ L.L.C. · CIK 0001855943 · Former 10% Owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

F1 · price: This amount represents the price per share of common stock, par value $0.0001 per share ("Common Stock"), of Custom Truck One Source, Inc. (the "Issuer") sold in a transaction exempt from registration pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended.

F5 · ownership.nature: Reflects shares of Common Stock directly held by Blackstone Energy Family Investment Partnership NQ ESC L.P. ("BE NQ").

F9 · ownership.nature: Blackstone Energy Management Associates NQ L.L.C. ("BEMA") is the general partner of BEP NQ and BEP CTOS. Blackstone EMA-NQ L.L.C. ("BEMA NQ") is the managing member of BEMA. BEP Side-by-Side GP NQ L.L.C. ("BEP GP") is the general partner of BE NQ. Blackstone Management Associates VI-NQ L.L.C. ("BMA NQ") is the general partner of BCP VI-NQ and BCP CTOS. BMA VI-NQ L.L.C. ("BMA VI-NQ") is the managing member of BMA NQ. Blackstone Family GP L.L.C. ("BS GP") is the general partner of BE SMD. BS GP is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. BCP VI-NQ Side-by-Side GP L.L.C. ("BCP GP") is the general partner of BE FIP.

F10 · ownership.nature: Blackstone Holdings III L.P. ("Holdings III") is the sole member of each of BEMA NQ, BEP GP and BMA VI-NQ. The general partner of Holdings III is Blackstone Holdings III GP L.P. ("Holdings III GP"). The general partner of Holdings III GP is Blackstone Holdings III GP Management L.L.C ("Holdings III GP Management"). Blackstone Holdings II L.P. ("Holdings II") is the sole member of BCP GP. Blackstone Holdings I/II GP L.L.C. ("Holdings I/II GP") is the general partner of Holdings II. Blackstone Inc. ("Blackstone") is the sole member of Holdings III GP Management and Holdings I/II GP. The sole holder of the Series II preferred stock of Blackstone is Blackstone Group Management L.L.C. ("BS Group Management"). BS Group Management is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman.

F11 · ownership.nature: Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person.

F12 · ownership.nature: Due to the limitations of the electronic filing system certain Reporting Persons are filing a separate Form 4.

F13 · ownership.nature: Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the securities reported herein for purposes of Section 16 of the Exchange Act or for any other purpose or that the Reporting Persons are subject to Section 16 of the Exchange Act.

SEC source: 0000899243-22-007080 · doc4.xml · nonDerivative · entry 3

Blackstone Energy Partners NQ L.P. · CIK 0001855931 · Former 10% Owner

BEP CTOS Holdings L.P. · CIK 0001857352 · Former 10% Owner

Blackstone Energy Family Investment Partnership SMD L.P. · CIK 0001851447 · Former 10% Owner

Blackstone Energy Family Investment Partnership NQ ESC L.P. · CIK 0001855942 · Former 10% Owner

Blackstone Capital Partners VI-NQ L.P. · CIK 0001855944 · Former 10% Owner

BCP CTOS Holdings L.P. · CIK 0001857351 · Former 10% Owner

Blackstone Family Investment Partnership VI-NQ ESC L.P. · CIK 0001856558 · Former 10% Owner

Blackstone Energy Management Associates NQ L.L.C. · CIK 0001855939 · Former 10% Owner

Blackstone EMA-NQ L.L.C. · CIK 0001855943 · Former 10% Owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

F1 · price: This amount represents the price per share of common stock, par value $0.0001 per share ("Common Stock"), of Custom Truck One Source, Inc. (the "Issuer") sold in a transaction exempt from registration pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended.

F4 · ownership.nature: Reflects shares of Common Stock directly held by Blackstone Energy Family Investment Partnership SMD L.P. ("BE SMD").

F9 · ownership.nature: Blackstone Energy Management Associates NQ L.L.C. ("BEMA") is the general partner of BEP NQ and BEP CTOS. Blackstone EMA-NQ L.L.C. ("BEMA NQ") is the managing member of BEMA. BEP Side-by-Side GP NQ L.L.C. ("BEP GP") is the general partner of BE NQ. Blackstone Management Associates VI-NQ L.L.C. ("BMA NQ") is the general partner of BCP VI-NQ and BCP CTOS. BMA VI-NQ L.L.C. ("BMA VI-NQ") is the managing member of BMA NQ. Blackstone Family GP L.L.C. ("BS GP") is the general partner of BE SMD. BS GP is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. BCP VI-NQ Side-by-Side GP L.L.C. ("BCP GP") is the general partner of BE FIP.

F10 · ownership.nature: Blackstone Holdings III L.P. ("Holdings III") is the sole member of each of BEMA NQ, BEP GP and BMA VI-NQ. The general partner of Holdings III is Blackstone Holdings III GP L.P. ("Holdings III GP"). The general partner of Holdings III GP is Blackstone Holdings III GP Management L.L.C ("Holdings III GP Management"). Blackstone Holdings II L.P. ("Holdings II") is the sole member of BCP GP. Blackstone Holdings I/II GP L.L.C. ("Holdings I/II GP") is the general partner of Holdings II. Blackstone Inc. ("Blackstone") is the sole member of Holdings III GP Management and Holdings I/II GP. The sole holder of the Series II preferred stock of Blackstone is Blackstone Group Management L.L.C. ("BS Group Management"). BS Group Management is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman.

F11 · ownership.nature: Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person.

F12 · ownership.nature: Due to the limitations of the electronic filing system certain Reporting Persons are filing a separate Form 4.

F13 · ownership.nature: Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the securities reported herein for purposes of Section 16 of the Exchange Act or for any other purpose or that the Reporting Persons are subject to Section 16 of the Exchange Act.

SEC source: 0000899243-22-007080 · doc4.xml · nonDerivative · entry 2

Blackstone Energy Partners NQ L.P. · CIK 0001855931 · Former 10% Owner

BEP CTOS Holdings L.P. · CIK 0001857352 · Former 10% Owner

Blackstone Energy Family Investment Partnership SMD L.P. · CIK 0001851447 · Former 10% Owner

Blackstone Energy Family Investment Partnership NQ ESC L.P. · CIK 0001855942 · Former 10% Owner

Blackstone Capital Partners VI-NQ L.P. · CIK 0001855944 · Former 10% Owner

BCP CTOS Holdings L.P. · CIK 0001857351 · Former 10% Owner

Blackstone Family Investment Partnership VI-NQ ESC L.P. · CIK 0001856558 · Former 10% Owner

Blackstone Energy Management Associates NQ L.L.C. · CIK 0001855939 · Former 10% Owner

Blackstone EMA-NQ L.L.C. · CIK 0001855943 · Former 10% Owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

F1 · price: This amount represents the price per share of common stock, par value $0.0001 per share ("Common Stock"), of Custom Truck One Source, Inc. (the "Issuer") sold in a transaction exempt from registration pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended.

F3 · ownership.nature: Reflects shares of Common Stock directly held by BEP CTOS Holdings L.P. ("BEP CTOS").

F9 · ownership.nature: Blackstone Energy Management Associates NQ L.L.C. ("BEMA") is the general partner of BEP NQ and BEP CTOS. Blackstone EMA-NQ L.L.C. ("BEMA NQ") is the managing member of BEMA. BEP Side-by-Side GP NQ L.L.C. ("BEP GP") is the general partner of BE NQ. Blackstone Management Associates VI-NQ L.L.C. ("BMA NQ") is the general partner of BCP VI-NQ and BCP CTOS. BMA VI-NQ L.L.C. ("BMA VI-NQ") is the managing member of BMA NQ. Blackstone Family GP L.L.C. ("BS GP") is the general partner of BE SMD. BS GP is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. BCP VI-NQ Side-by-Side GP L.L.C. ("BCP GP") is the general partner of BE FIP.

F10 · ownership.nature: Blackstone Holdings III L.P. ("Holdings III") is the sole member of each of BEMA NQ, BEP GP and BMA VI-NQ. The general partner of Holdings III is Blackstone Holdings III GP L.P. ("Holdings III GP"). The general partner of Holdings III GP is Blackstone Holdings III GP Management L.L.C ("Holdings III GP Management"). Blackstone Holdings II L.P. ("Holdings II") is the sole member of BCP GP. Blackstone Holdings I/II GP L.L.C. ("Holdings I/II GP") is the general partner of Holdings II. Blackstone Inc. ("Blackstone") is the sole member of Holdings III GP Management and Holdings I/II GP. The sole holder of the Series II preferred stock of Blackstone is Blackstone Group Management L.L.C. ("BS Group Management"). BS Group Management is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman.

F11 · ownership.nature: Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person.

F12 · ownership.nature: Due to the limitations of the electronic filing system certain Reporting Persons are filing a separate Form 4.

F13 · ownership.nature: Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the securities reported herein for purposes of Section 16 of the Exchange Act or for any other purpose or that the Reporting Persons are subject to Section 16 of the Exchange Act.

SEC source: 0000899243-22-007080 · doc4.xml · nonDerivative · entry 1

Blackstone Energy Partners NQ L.P. · CIK 0001855931 · Former 10% Owner

BEP CTOS Holdings L.P. · CIK 0001857352 · Former 10% Owner

Blackstone Energy Family Investment Partnership SMD L.P. · CIK 0001851447 · Former 10% Owner

Blackstone Energy Family Investment Partnership NQ ESC L.P. · CIK 0001855942 · Former 10% Owner

Blackstone Capital Partners VI-NQ L.P. · CIK 0001855944 · Former 10% Owner

BCP CTOS Holdings L.P. · CIK 0001857351 · Former 10% Owner

Blackstone Family Investment Partnership VI-NQ ESC L.P. · CIK 0001856558 · Former 10% Owner

Blackstone Energy Management Associates NQ L.L.C. · CIK 0001855939 · Former 10% Owner

Blackstone EMA-NQ L.L.C. · CIK 0001855943 · Former 10% Owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

F1 · price: This amount represents the price per share of common stock, par value $0.0001 per share ("Common Stock"), of Custom Truck One Source, Inc. (the "Issuer") sold in a transaction exempt from registration pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended.

F2 · ownership.nature: Reflects shares of Common Stock directly held by Blackstone Energy Partners NQ L.P. ("BEP NQ").

F9 · ownership.nature: Blackstone Energy Management Associates NQ L.L.C. ("BEMA") is the general partner of BEP NQ and BEP CTOS. Blackstone EMA-NQ L.L.C. ("BEMA NQ") is the managing member of BEMA. BEP Side-by-Side GP NQ L.L.C. ("BEP GP") is the general partner of BE NQ. Blackstone Management Associates VI-NQ L.L.C. ("BMA NQ") is the general partner of BCP VI-NQ and BCP CTOS. BMA VI-NQ L.L.C. ("BMA VI-NQ") is the managing member of BMA NQ. Blackstone Family GP L.L.C. ("BS GP") is the general partner of BE SMD. BS GP is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. BCP VI-NQ Side-by-Side GP L.L.C. ("BCP GP") is the general partner of BE FIP.

F10 · ownership.nature: Blackstone Holdings III L.P. ("Holdings III") is the sole member of each of BEMA NQ, BEP GP and BMA VI-NQ. The general partner of Holdings III is Blackstone Holdings III GP L.P. ("Holdings III GP"). The general partner of Holdings III GP is Blackstone Holdings III GP Management L.L.C ("Holdings III GP Management"). Blackstone Holdings II L.P. ("Holdings II") is the sole member of BCP GP. Blackstone Holdings I/II GP L.L.C. ("Holdings I/II GP") is the general partner of Holdings II. Blackstone Inc. ("Blackstone") is the sole member of Holdings III GP Management and Holdings I/II GP. The sole holder of the Series II preferred stock of Blackstone is Blackstone Group Management L.L.C. ("BS Group Management"). BS Group Management is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman.

F11 · ownership.nature: Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person.

F12 · ownership.nature: Due to the limitations of the electronic filing system certain Reporting Persons are filing a separate Form 4.

F13 · ownership.nature: Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the securities reported herein for purposes of Section 16 of the Exchange Act or for any other purpose or that the Reporting Persons are subject to Section 16 of the Exchange Act.

SEC source: 0000899243-22-007082 · doc4.xml · nonDerivative · entry 7

Blackstone Holdings II L.P. · CIK 0001484870 · Former 10% Owner

BLACKSTONE FAMILY GP LLC · CIK 0001404964 · Former 10% Owner

BEP Side-by-Side GP NQ L.L.C. · CIK 0001857354 · Former 10% Owner

Blackstone Management Associates VI-NQ L.L.C. · CIK 0001855930 · Former 10% Owner

BMA VI-NQ L.L.C. · CIK 0001855977 · Former 10% Owner

Blackstone Holdings III GP L.P. · CIK 0001478809 · Former 10% Owner

Blackstone Holdings III GP Management L.L.C. · CIK 0001478815 · Former 10% Owner

BCP VI-NQ Side-by-Side GP L.L.C. · CIK 0001856561 · Former 10% Owner

Blackstone Holdings I/II GP L.L.C. · CIK 0001464695 · Former 10% Owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

F1 · price: This amount represents the price per share of common stock, par value $0.0001 per share ("Common Stock"), of Custom Truck One Source, Inc. (the "Issuer") sold in a transaction exempt from registration pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended.

F8 · ownership.nature: Reflects shares of Common Stock directly held by Blackstone Family Investment Partnership VI-NQ ESC L.P. ("BE FIP").

F9 · ownership.nature: Blackstone Energy Management Associates NQ L.L.C. ("BEMA") is the general partner of BEP NQ and BEP CTOS. Blackstone EMA-NQ L.L.C. ("BEMA NQ") is the managing member of BEMA. BEP Side-by-Side GP NQ L.L.C. ("BEP GP") is the general partner of BE NQ. Blackstone Management Associates VI-NQ L.L.C. ("BMA NQ") is the general partner of BCP VI-NQ and BCP CTOS. BMA VI-NQ L.L.C. ("BMA VI-NQ") is the managing member of BMA NQ. Blackstone Family GP L.L.C. ("BS GP") is the general partner of BE SMD. BS GP is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. BCP VI-NQ Side-by-Side GP L.L.C. ("BCP GP") is the general partner of BE FIP.

F10 · ownership.nature: Blackstone Holdings III L.P. ("Holdings III") is the sole member of each of BEMA NQ, BEP GP and BMA VI-NQ. The general partner of Holdings III is Blackstone Holdings III GP L.P. ("Holdings III GP"). The general partner of Holdings III GP is Blackstone Holdings III GP Management L.L.C ("Holdings III GP Management"). Blackstone Holdings II L.P. ("Holdings II") is the sole member of BCP GP. Blackstone Holdings I/II GP L.L.C. ("Holdings I/II GP") is the general partner of Holdings II. Blackstone Inc. ("Blackstone") is the sole member of Holdings III GP Management and Holdings I/II GP. The sole holder of the Series II preferred stock of Blackstone is Blackstone Group Management L.L.C. ("BS Group Management"). BS Group Management is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman.

F11 · ownership.nature: Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person.

F12 · ownership.nature: Due to the limitations of the electronic filing system certain Reporting Persons are filing a separate Form 4.

F13 · ownership.nature: Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the securities reported herein for purposes of Section 16 of the Exchange Act or for any other purpose or that the Reporting Persons are subject to Section 16 of the Exchange Act.

SEC source: 0000899243-22-007082 · doc4.xml · nonDerivative · entry 6

Blackstone Holdings II L.P. · CIK 0001484870 · Former 10% Owner

BLACKSTONE FAMILY GP LLC · CIK 0001404964 · Former 10% Owner

BEP Side-by-Side GP NQ L.L.C. · CIK 0001857354 · Former 10% Owner

Blackstone Management Associates VI-NQ L.L.C. · CIK 0001855930 · Former 10% Owner

BMA VI-NQ L.L.C. · CIK 0001855977 · Former 10% Owner

Blackstone Holdings III GP L.P. · CIK 0001478809 · Former 10% Owner

Blackstone Holdings III GP Management L.L.C. · CIK 0001478815 · Former 10% Owner

BCP VI-NQ Side-by-Side GP L.L.C. · CIK 0001856561 · Former 10% Owner

Blackstone Holdings I/II GP L.L.C. · CIK 0001464695 · Former 10% Owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

F1 · price: This amount represents the price per share of common stock, par value $0.0001 per share ("Common Stock"), of Custom Truck One Source, Inc. (the "Issuer") sold in a transaction exempt from registration pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended.

F7 · ownership.nature: Reflects shares of Common Stock directly held by BCP CTOS Holdings L.P. ("BCP CTOS").

F9 · ownership.nature: Blackstone Energy Management Associates NQ L.L.C. ("BEMA") is the general partner of BEP NQ and BEP CTOS. Blackstone EMA-NQ L.L.C. ("BEMA NQ") is the managing member of BEMA. BEP Side-by-Side GP NQ L.L.C. ("BEP GP") is the general partner of BE NQ. Blackstone Management Associates VI-NQ L.L.C. ("BMA NQ") is the general partner of BCP VI-NQ and BCP CTOS. BMA VI-NQ L.L.C. ("BMA VI-NQ") is the managing member of BMA NQ. Blackstone Family GP L.L.C. ("BS GP") is the general partner of BE SMD. BS GP is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. BCP VI-NQ Side-by-Side GP L.L.C. ("BCP GP") is the general partner of BE FIP.

F10 · ownership.nature: Blackstone Holdings III L.P. ("Holdings III") is the sole member of each of BEMA NQ, BEP GP and BMA VI-NQ. The general partner of Holdings III is Blackstone Holdings III GP L.P. ("Holdings III GP"). The general partner of Holdings III GP is Blackstone Holdings III GP Management L.L.C ("Holdings III GP Management"). Blackstone Holdings II L.P. ("Holdings II") is the sole member of BCP GP. Blackstone Holdings I/II GP L.L.C. ("Holdings I/II GP") is the general partner of Holdings II. Blackstone Inc. ("Blackstone") is the sole member of Holdings III GP Management and Holdings I/II GP. The sole holder of the Series II preferred stock of Blackstone is Blackstone Group Management L.L.C. ("BS Group Management"). BS Group Management is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman.

F11 · ownership.nature: Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person.

F12 · ownership.nature: Due to the limitations of the electronic filing system certain Reporting Persons are filing a separate Form 4.

F13 · ownership.nature: Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the securities reported herein for purposes of Section 16 of the Exchange Act or for any other purpose or that the Reporting Persons are subject to Section 16 of the Exchange Act.

SEC source: 0000899243-22-007082 · doc4.xml · nonDerivative · entry 5

Blackstone Holdings II L.P. · CIK 0001484870 · Former 10% Owner

BLACKSTONE FAMILY GP LLC · CIK 0001404964 · Former 10% Owner

BEP Side-by-Side GP NQ L.L.C. · CIK 0001857354 · Former 10% Owner

Blackstone Management Associates VI-NQ L.L.C. · CIK 0001855930 · Former 10% Owner

BMA VI-NQ L.L.C. · CIK 0001855977 · Former 10% Owner

Blackstone Holdings III GP L.P. · CIK 0001478809 · Former 10% Owner

Blackstone Holdings III GP Management L.L.C. · CIK 0001478815 · Former 10% Owner

BCP VI-NQ Side-by-Side GP L.L.C. · CIK 0001856561 · Former 10% Owner

Blackstone Holdings I/II GP L.L.C. · CIK 0001464695 · Former 10% Owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

F1 · price: This amount represents the price per share of common stock, par value $0.0001 per share ("Common Stock"), of Custom Truck One Source, Inc. (the "Issuer") sold in a transaction exempt from registration pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended.

F6 · ownership.nature: Reflects shares of Common Stock directly held by Blackstone Capital Partners VI-NQ L.P. ("BCP VI-NQ").

F9 · ownership.nature: Blackstone Energy Management Associates NQ L.L.C. ("BEMA") is the general partner of BEP NQ and BEP CTOS. Blackstone EMA-NQ L.L.C. ("BEMA NQ") is the managing member of BEMA. BEP Side-by-Side GP NQ L.L.C. ("BEP GP") is the general partner of BE NQ. Blackstone Management Associates VI-NQ L.L.C. ("BMA NQ") is the general partner of BCP VI-NQ and BCP CTOS. BMA VI-NQ L.L.C. ("BMA VI-NQ") is the managing member of BMA NQ. Blackstone Family GP L.L.C. ("BS GP") is the general partner of BE SMD. BS GP is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. BCP VI-NQ Side-by-Side GP L.L.C. ("BCP GP") is the general partner of BE FIP.

F10 · ownership.nature: Blackstone Holdings III L.P. ("Holdings III") is the sole member of each of BEMA NQ, BEP GP and BMA VI-NQ. The general partner of Holdings III is Blackstone Holdings III GP L.P. ("Holdings III GP"). The general partner of Holdings III GP is Blackstone Holdings III GP Management L.L.C ("Holdings III GP Management"). Blackstone Holdings II L.P. ("Holdings II") is the sole member of BCP GP. Blackstone Holdings I/II GP L.L.C. ("Holdings I/II GP") is the general partner of Holdings II. Blackstone Inc. ("Blackstone") is the sole member of Holdings III GP Management and Holdings I/II GP. The sole holder of the Series II preferred stock of Blackstone is Blackstone Group Management L.L.C. ("BS Group Management"). BS Group Management is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman.

F11 · ownership.nature: Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person.

F12 · ownership.nature: Due to the limitations of the electronic filing system certain Reporting Persons are filing a separate Form 4.

F13 · ownership.nature: Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the securities reported herein for purposes of Section 16 of the Exchange Act or for any other purpose or that the Reporting Persons are subject to Section 16 of the Exchange Act.

SEC source: 0000899243-22-007082 · doc4.xml · nonDerivative · entry 4

Blackstone Holdings II L.P. · CIK 0001484870 · Former 10% Owner

BLACKSTONE FAMILY GP LLC · CIK 0001404964 · Former 10% Owner

BEP Side-by-Side GP NQ L.L.C. · CIK 0001857354 · Former 10% Owner

Blackstone Management Associates VI-NQ L.L.C. · CIK 0001855930 · Former 10% Owner

BMA VI-NQ L.L.C. · CIK 0001855977 · Former 10% Owner

Blackstone Holdings III GP L.P. · CIK 0001478809 · Former 10% Owner

Blackstone Holdings III GP Management L.L.C. · CIK 0001478815 · Former 10% Owner

BCP VI-NQ Side-by-Side GP L.L.C. · CIK 0001856561 · Former 10% Owner

Blackstone Holdings I/II GP L.L.C. · CIK 0001464695 · Former 10% Owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

F1 · price: This amount represents the price per share of common stock, par value $0.0001 per share ("Common Stock"), of Custom Truck One Source, Inc. (the "Issuer") sold in a transaction exempt from registration pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended.

F5 · ownership.nature: Reflects shares of Common Stock directly held by Blackstone Energy Family Investment Partnership NQ ESC L.P. ("BE NQ").

F9 · ownership.nature: Blackstone Energy Management Associates NQ L.L.C. ("BEMA") is the general partner of BEP NQ and BEP CTOS. Blackstone EMA-NQ L.L.C. ("BEMA NQ") is the managing member of BEMA. BEP Side-by-Side GP NQ L.L.C. ("BEP GP") is the general partner of BE NQ. Blackstone Management Associates VI-NQ L.L.C. ("BMA NQ") is the general partner of BCP VI-NQ and BCP CTOS. BMA VI-NQ L.L.C. ("BMA VI-NQ") is the managing member of BMA NQ. Blackstone Family GP L.L.C. ("BS GP") is the general partner of BE SMD. BS GP is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. BCP VI-NQ Side-by-Side GP L.L.C. ("BCP GP") is the general partner of BE FIP.

F10 · ownership.nature: Blackstone Holdings III L.P. ("Holdings III") is the sole member of each of BEMA NQ, BEP GP and BMA VI-NQ. The general partner of Holdings III is Blackstone Holdings III GP L.P. ("Holdings III GP"). The general partner of Holdings III GP is Blackstone Holdings III GP Management L.L.C ("Holdings III GP Management"). Blackstone Holdings II L.P. ("Holdings II") is the sole member of BCP GP. Blackstone Holdings I/II GP L.L.C. ("Holdings I/II GP") is the general partner of Holdings II. Blackstone Inc. ("Blackstone") is the sole member of Holdings III GP Management and Holdings I/II GP. The sole holder of the Series II preferred stock of Blackstone is Blackstone Group Management L.L.C. ("BS Group Management"). BS Group Management is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman.

F11 · ownership.nature: Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person.

F12 · ownership.nature: Due to the limitations of the electronic filing system certain Reporting Persons are filing a separate Form 4.

F13 · ownership.nature: Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the securities reported herein for purposes of Section 16 of the Exchange Act or for any other purpose or that the Reporting Persons are subject to Section 16 of the Exchange Act.

SEC source: 0000899243-22-007082 · doc4.xml · nonDerivative · entry 3

Blackstone Holdings II L.P. · CIK 0001484870 · Former 10% Owner

BLACKSTONE FAMILY GP LLC · CIK 0001404964 · Former 10% Owner

BEP Side-by-Side GP NQ L.L.C. · CIK 0001857354 · Former 10% Owner

Blackstone Management Associates VI-NQ L.L.C. · CIK 0001855930 · Former 10% Owner

BMA VI-NQ L.L.C. · CIK 0001855977 · Former 10% Owner

Blackstone Holdings III GP L.P. · CIK 0001478809 · Former 10% Owner

Blackstone Holdings III GP Management L.L.C. · CIK 0001478815 · Former 10% Owner

BCP VI-NQ Side-by-Side GP L.L.C. · CIK 0001856561 · Former 10% Owner

Blackstone Holdings I/II GP L.L.C. · CIK 0001464695 · Former 10% Owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

F1 · price: This amount represents the price per share of common stock, par value $0.0001 per share ("Common Stock"), of Custom Truck One Source, Inc. (the "Issuer") sold in a transaction exempt from registration pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended.

F4 · ownership.nature: Reflects shares of Common Stock directly held by Blackstone Energy Family Investment Partnership SMD L.P. ("BE SMD").

F9 · ownership.nature: Blackstone Energy Management Associates NQ L.L.C. ("BEMA") is the general partner of BEP NQ and BEP CTOS. Blackstone EMA-NQ L.L.C. ("BEMA NQ") is the managing member of BEMA. BEP Side-by-Side GP NQ L.L.C. ("BEP GP") is the general partner of BE NQ. Blackstone Management Associates VI-NQ L.L.C. ("BMA NQ") is the general partner of BCP VI-NQ and BCP CTOS. BMA VI-NQ L.L.C. ("BMA VI-NQ") is the managing member of BMA NQ. Blackstone Family GP L.L.C. ("BS GP") is the general partner of BE SMD. BS GP is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. BCP VI-NQ Side-by-Side GP L.L.C. ("BCP GP") is the general partner of BE FIP.

F10 · ownership.nature: Blackstone Holdings III L.P. ("Holdings III") is the sole member of each of BEMA NQ, BEP GP and BMA VI-NQ. The general partner of Holdings III is Blackstone Holdings III GP L.P. ("Holdings III GP"). The general partner of Holdings III GP is Blackstone Holdings III GP Management L.L.C ("Holdings III GP Management"). Blackstone Holdings II L.P. ("Holdings II") is the sole member of BCP GP. Blackstone Holdings I/II GP L.L.C. ("Holdings I/II GP") is the general partner of Holdings II. Blackstone Inc. ("Blackstone") is the sole member of Holdings III GP Management and Holdings I/II GP. The sole holder of the Series II preferred stock of Blackstone is Blackstone Group Management L.L.C. ("BS Group Management"). BS Group Management is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman.

F11 · ownership.nature: Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person.

F12 · ownership.nature: Due to the limitations of the electronic filing system certain Reporting Persons are filing a separate Form 4.

F13 · ownership.nature: Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the securities reported herein for purposes of Section 16 of the Exchange Act or for any other purpose or that the Reporting Persons are subject to Section 16 of the Exchange Act.

SEC source: 0000899243-22-007082 · doc4.xml · nonDerivative · entry 2

Blackstone Holdings II L.P. · CIK 0001484870 · Former 10% Owner

BLACKSTONE FAMILY GP LLC · CIK 0001404964 · Former 10% Owner

BEP Side-by-Side GP NQ L.L.C. · CIK 0001857354 · Former 10% Owner

Blackstone Management Associates VI-NQ L.L.C. · CIK 0001855930 · Former 10% Owner

BMA VI-NQ L.L.C. · CIK 0001855977 · Former 10% Owner

Blackstone Holdings III GP L.P. · CIK 0001478809 · Former 10% Owner

Blackstone Holdings III GP Management L.L.C. · CIK 0001478815 · Former 10% Owner

BCP VI-NQ Side-by-Side GP L.L.C. · CIK 0001856561 · Former 10% Owner

Blackstone Holdings I/II GP L.L.C. · CIK 0001464695 · Former 10% Owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

F1 · price: This amount represents the price per share of common stock, par value $0.0001 per share ("Common Stock"), of Custom Truck One Source, Inc. (the "Issuer") sold in a transaction exempt from registration pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended.

F3 · ownership.nature: Reflects shares of Common Stock directly held by BEP CTOS Holdings L.P. ("BEP CTOS").

F9 · ownership.nature: Blackstone Energy Management Associates NQ L.L.C. ("BEMA") is the general partner of BEP NQ and BEP CTOS. Blackstone EMA-NQ L.L.C. ("BEMA NQ") is the managing member of BEMA. BEP Side-by-Side GP NQ L.L.C. ("BEP GP") is the general partner of BE NQ. Blackstone Management Associates VI-NQ L.L.C. ("BMA NQ") is the general partner of BCP VI-NQ and BCP CTOS. BMA VI-NQ L.L.C. ("BMA VI-NQ") is the managing member of BMA NQ. Blackstone Family GP L.L.C. ("BS GP") is the general partner of BE SMD. BS GP is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. BCP VI-NQ Side-by-Side GP L.L.C. ("BCP GP") is the general partner of BE FIP.

F10 · ownership.nature: Blackstone Holdings III L.P. ("Holdings III") is the sole member of each of BEMA NQ, BEP GP and BMA VI-NQ. The general partner of Holdings III is Blackstone Holdings III GP L.P. ("Holdings III GP"). The general partner of Holdings III GP is Blackstone Holdings III GP Management L.L.C ("Holdings III GP Management"). Blackstone Holdings II L.P. ("Holdings II") is the sole member of BCP GP. Blackstone Holdings I/II GP L.L.C. ("Holdings I/II GP") is the general partner of Holdings II. Blackstone Inc. ("Blackstone") is the sole member of Holdings III GP Management and Holdings I/II GP. The sole holder of the Series II preferred stock of Blackstone is Blackstone Group Management L.L.C. ("BS Group Management"). BS Group Management is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman.

F11 · ownership.nature: Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person.

F12 · ownership.nature: Due to the limitations of the electronic filing system certain Reporting Persons are filing a separate Form 4.

F13 · ownership.nature: Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the securities reported herein for purposes of Section 16 of the Exchange Act or for any other purpose or that the Reporting Persons are subject to Section 16 of the Exchange Act.

SEC source: 0000899243-22-007082 · doc4.xml · nonDerivative · entry 1

Blackstone Holdings II L.P. · CIK 0001484870 · Former 10% Owner

BLACKSTONE FAMILY GP LLC · CIK 0001404964 · Former 10% Owner

BEP Side-by-Side GP NQ L.L.C. · CIK 0001857354 · Former 10% Owner

Blackstone Management Associates VI-NQ L.L.C. · CIK 0001855930 · Former 10% Owner

BMA VI-NQ L.L.C. · CIK 0001855977 · Former 10% Owner

Blackstone Holdings III GP L.P. · CIK 0001478809 · Former 10% Owner

Blackstone Holdings III GP Management L.L.C. · CIK 0001478815 · Former 10% Owner

BCP VI-NQ Side-by-Side GP L.L.C. · CIK 0001856561 · Former 10% Owner

Blackstone Holdings I/II GP L.L.C. · CIK 0001464695 · Former 10% Owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

F1 · price: This amount represents the price per share of common stock, par value $0.0001 per share ("Common Stock"), of Custom Truck One Source, Inc. (the "Issuer") sold in a transaction exempt from registration pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended.

F2 · ownership.nature: Reflects shares of Common Stock directly held by Blackstone Energy Partners NQ L.P. ("BEP NQ").

F9 · ownership.nature: Blackstone Energy Management Associates NQ L.L.C. ("BEMA") is the general partner of BEP NQ and BEP CTOS. Blackstone EMA-NQ L.L.C. ("BEMA NQ") is the managing member of BEMA. BEP Side-by-Side GP NQ L.L.C. ("BEP GP") is the general partner of BE NQ. Blackstone Management Associates VI-NQ L.L.C. ("BMA NQ") is the general partner of BCP VI-NQ and BCP CTOS. BMA VI-NQ L.L.C. ("BMA VI-NQ") is the managing member of BMA NQ. Blackstone Family GP L.L.C. ("BS GP") is the general partner of BE SMD. BS GP is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. BCP VI-NQ Side-by-Side GP L.L.C. ("BCP GP") is the general partner of BE FIP.

F10 · ownership.nature: Blackstone Holdings III L.P. ("Holdings III") is the sole member of each of BEMA NQ, BEP GP and BMA VI-NQ. The general partner of Holdings III is Blackstone Holdings III GP L.P. ("Holdings III GP"). The general partner of Holdings III GP is Blackstone Holdings III GP Management L.L.C ("Holdings III GP Management"). Blackstone Holdings II L.P. ("Holdings II") is the sole member of BCP GP. Blackstone Holdings I/II GP L.L.C. ("Holdings I/II GP") is the general partner of Holdings II. Blackstone Inc. ("Blackstone") is the sole member of Holdings III GP Management and Holdings I/II GP. The sole holder of the Series II preferred stock of Blackstone is Blackstone Group Management L.L.C. ("BS Group Management"). BS Group Management is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman.

F11 · ownership.nature: Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person.

F12 · ownership.nature: Due to the limitations of the electronic filing system certain Reporting Persons are filing a separate Form 4.

F13 · ownership.nature: Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the securities reported herein for purposes of Section 16 of the Exchange Act or for any other purpose or that the Reporting Persons are subject to Section 16 of the Exchange Act.

SEC source: 0000899243-22-007083 · doc4.xml · nonDerivative · entry 7

Blackstone Holdings III L.P. · CIK 0001404073 · Former 10% Owner

Blackstone Inc · CIK 0001393818 · Former 10% Owner

Blackstone Group Management L.L.C. · CIK 0001404071 · Former 10% Owner

SCHWARZMAN STEPHEN A · CIK 0001070844 · Former 10% Owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

F1 · price: This amount represents the price per share of common stock, par value $0.0001 per share ("Common Stock"), of Custom Truck One Source, Inc. (the "Issuer") sold in a transaction exempt from registration pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended.

F8 · ownership.nature: Reflects shares of Common Stock directly held by Blackstone Family Investment Partnership VI-NQ ESC L.P. ("BE FIP").

F9 · ownership.nature: Blackstone Energy Management Associates NQ L.L.C. ("BEMA") is the general partner of BEP NQ and BEP CTOS. Blackstone EMA-NQ L.L.C. ("BEMA NQ") is the managing member of BEMA. BEP Side-by-Side GP NQ L.L.C. ("BEP GP") is the general partner of BE NQ. Blackstone Management Associates VI-NQ L.L.C. ("BMA NQ") is the general partner of BCP VI-NQ and BCP CTOS. BMA VI-NQ L.L.C. ("BMA VI-NQ") is the managing member of BMA NQ. Blackstone Family GP L.L.C. ("BS GP") is the general partner of BE SMD. BS GP is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. BCP VI-NQ Side-by-Side GP L.L.C. ("BCP GP") is the general partner of BE FIP.

F10 · ownership.nature: Blackstone Holdings III L.P. ("Holdings III") is the sole member of each of BEMA NQ, BEP GP and BMA VI-NQ. The general partner of Holdings III is Blackstone Holdings III GP L.P. ("Holdings III GP"). The general partner of Holdings III GP is Blackstone Holdings III GP Management L.L.C ("Holdings III GP Management"). Blackstone Holdings II L.P. ("Holdings II") is the sole member of BCP GP. Blackstone Holdings I/II GP L.L.C. ("Holdings I/II GP") is the general partner of Holdings II. Blackstone Inc. ("Blackstone") is the sole member of Holdings III GP Management and Holdings I/II GP. The sole holder of the Series II preferred stock of Blackstone is Blackstone Group Management L.L.C. ("BS Group Management"). BS Group Management is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman.

F11 · ownership.nature: Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person.

F12 · ownership.nature: Due to the limitations of the electronic filing system certain Reporting Persons are filing a separate Form 4.

F13 · ownership.nature: Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the securities reported herein for purposes of Section 16 of the Exchange Act or for any other purpose or that the Reporting Persons are subject to Section 16 of the Exchange Act.