SC 13D/A

NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH

SOLE VOTING POWER

382,460

SHARED VOTING POWER

0

SOLE DISPOSITIVE POWER

382,460

SHARED DISPOSITIVE POWER

0

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 1)

Custom Truck One Source, Inc.

(Name of Issuer)

Common Stock, par value $0.0001 per share

(Title of Class of Securities)

64083J104

(CUSIP Number)

John G. Finley

Blackstone Inc.

345 Park Avenue

New York, New York 10154

Tel: (212) 583-5000

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

November 17, 2021

(Date of Event Which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box. ☐

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Rule 13d-7 for other parties to whom copies are to be sent.

*	The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone Energy Partners NQ L.P.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS BEP CTOS Holdings L.P.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone Energy Family Investment Partnership SMD L.P.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone Energy Family Investment Partnership NQ ESC L.P.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone Capital Partners VI-NQ L.P.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS BCP CTOS Holdings L.P.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone Family Investment Partnership VI-NQ ESC L.P.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone Energy Management Associates NQ L.L.C.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone EMA-NQ L.L.C.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone Family GP L.L.C.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS BEP Side-by-Side GP NQ L.L.C.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone Management Associates VI-NQ L.L.C.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS BMA VI-NQ L.L.C.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone Holdings III L.P.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone Holdings III GP L.P.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone Holdings III GP Management L.L.C.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS BCP VI-NQ Side-by-Side GP L.L.C.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone Holdings II L.P.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone Holdings I/II GP L.L.C.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone Inc.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Blackstone Group Management L.L.C.
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

CUSIP No. 64083J104


1		NAMES OF REPORTING PERSONS Stephen A. Schwarzman
2		CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a) ☐ (b) ☒
3		SEC USE ONLY
4		SOURCE OF FUNDS (SEE INSTRUCTIONS) OO
5		CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E) ☐
6		CITIZENSHIP OR PLACE OF ORGANIZATION United States

This Amendment No. 1 (“Amendment No. 1”) amends and supplements the Schedule 13D originally filed with the Securities and Exchange Commission (the “SEC”) by the Reporting Persons on April 12, 2021 (the “Original Schedule 13D,” and as amended by Amendment No. 1, the “Schedule 13D”). Capitalized terms used but not defined herein have the meanings ascribed to them in the Schedule 13D. Except as expressly set forth herein, there have been no changes to the information set forth in the Schedule 13D.

Item 4.

Purpose of Transaction

Item 4 of the Schedule 13D is hereby amended and supplemented by adding the following:

On November 17, 2021, in connection with a registered secondary public offering (the “Secondary Offering”) of Common Stock, the Issuer, Blackstone Energy Partners NQ L.P., a Delaware limited partnership, BEP CTOS Holdings L.P., a Delaware limited partnership, Blackstone Energy Family Investment Partnership SMD L.P., a Delaware limited partnership, Blackstone Energy Family Investment Partnership NQ ESC L.P., a Delaware limited partnership, Blackstone Capital Partners VI-NQ L.P., a Delaware limited partnership, BCP CTOS Holdings L.P., a Delaware limited partnership, and Blackstone Family Investment Partnership VI-NQ ESC L.P., a Delaware limited partnership (collectively, the “Blackstone Funds”) and the underwriters party thereto (the “Underwriters”), entered into an underwriting agreement (the “Underwriting Agreement”) pursuant to which the Blackstone Funds agreed to sell to the Underwriters, and the Underwriters agreed to purchase from the Blackstone Funds, subject to and upon the terms and conditions set forth therein, 12,322,975 shares of Common Stock at a price of $8.50 share. The Blackstone Funds also granted the Underwriters a 30-day option (the “Over-allotment Option”) to purchase up to 1,848,446 shares of Common Stock at a price to the public of $8.50 per share, with net proceeds to the Blackstone funds of $8.2025 per share. The Underwriters have not yet exercised their Over-allotment Option, and the Blackstone Funds completed the Secondary Offering on November 22, 2021.

Pursuant to the Underwriting Agreement, the Blackstone Funds have entered into a lock-up agreement (the “Lock-Up Agreement”) with the Underwriters pursuant to which each has agreed with the Underwriters, subject to customary exceptions, not to offer, sell, contract to sell, pledge, grant any option to purchase, make any short sale or otherwise dispose of any shares of Common Stock, or any options or warrants to purchase any shares of Common Stock, or any securities convertible into, exchangeable for or that represent the right to receive shares of Common Stock during the period from November 17, 2021 continuing through the date 60 days thereafter, other than shares of Common Stock disposed of as bona fide gifts approved by Citigroup Global Markets Inc. The foregoing descriptions of the Underwriting Agreement and the Lock-Up Agreement set forth in this Item 4 do not purport to be complete and are qualified in their entirety by reference to the full text of the Underwriting Agreement and the Lock-Up Agreement, which have been filed as Exhibit C and Exhibit D hereto and are incorporated herein by reference.

Item 5.

Interest in Securities of the Issuer

Item 5 of the Schedule 13D is hereby amended and restated as follows:

(a) and (b) Calculations of the percentage of the shares of Common Stock beneficially owned assumes that there were 247,311,494 shares of Common Stock outstanding as stated in the prospectus supplement dated November 17, 2021 and filed with the SEC on November 22, 2021. The aggregate number and percentage of the Common Stock beneficially owned by each Reporting Person and, for each Reporting Person, the number of shares as to which there is sole power to vote or to direct the vote, shared power to vote or to direct the vote, sole power to dispose or to direct the disposition, or shared power to dispose or to direct the disposition are set forth on rows 7 through 11 and row 13 of the cover pages of this Schedule 13D and are incorporated herein by reference.

As of the date hereof, (i) Blackstone Energy Partners NQ L.P. directly holds 382,460 shares of Common Stock, (ii) BEP CTOS Holdings L.P. directly holds 472,446 shares of Common Stock, (iii) Blackstone Energy Family Investment Partnership SMD L.P. directly holds 45,860 shares of Common Stock, (iv) Blackstone Energy Family Investment Partnership NQ ESC L.P. directly holds 3,457 shares of Common Stock, (v) Blackstone Capital Partners VI-NQ L.P. directly holds 455,487 shares of Common Stock, and (vi) BCP CTOS Holdings L.P. directly holds 466,472 shares of Common Stock, and (vii) Blackstone Family Investment Partnership VI-NQ ESC L.P. directly holds 2,264 shares of Common Stock.

Blackstone Energy Management Associates NQ L.L.C. is the general partner of Blackstone Energy Partners NQ L.P. and BEP CTOS Holdings L.P. Blackstone EMA-NQ L.L.C. is the managing member of Blackstone Energy Management Associates NQ L.L.C. BEP Side-by-Side GP NQ L.L.C. is the general partner of Blackstone Energy Family Investment Partnership NQ ESC L.P. Blackstone Management Associates VI-NQ L.L.C. is the general partner of Blackstone Capital Partners VI-NQ L.P. and BCP CTOS Holdings L.P. BMA VI-NQ L.L.C. is the managing member of Blackstone Management Associates VI-NQ L.L.C. Blackstone Family GP L.L.C. is the general partner of Blackstone Energy Family Investment Partnership SMD L.P. Blackstone Family GP L.L.C. 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. is the general partner of Blackstone Family Investment Partnership VI-NQ ESC L.P. Blackstone Holdings III L.P. is the sole member of each of Blackstone EMA-NQ L.L.C., BEP Side-by-Side GP NQ L.L.C. and BMA VI-NQ L.L.C. The general partner of Blackstone Holdings III L.P. is Blackstone Holdings III GP L.P. The general partner of Blackstone Holdings III GP L.P. is Blackstone Holdings III GP Management L.L.C. Blackstone Holdings II L.P. is the sole member of BCP VI-NQ Side-by-Side GP L.L.C. Blackstone Holdings I/II GP L.L.C. is the general partner of Blackstone Holdings II L.P. Blackstone Inc. is the sole member of Blackstone Holdings III GP Management L.L.C and Blackstone Holdings I/II GP L.L.C. The sole holder of the Series II preferred stock of Blackstone Inc. is Blackstone Group Management L.L.C. Blackstone Group Management L.L.C. is wholly-owned by Blackstone’s senior managing directors and controlled by its founder, Stephen A. Schwarzman.

Neither the filing of this Amendment No. 1 nor any of its contents shall be deemed to constitute an admission that any Reporting Person is the beneficial owner of the Common Stock referred to herein for purposes of Section 13(d) of the Exchange Act or for any other purpose and each of the Reporting Persons expressly disclaims beneficial ownership of such shares of Common Stock.

By virtue of the Stockholders’ Agreement, the Reporting Persons and the other persons party thereto may each be deemed to be a member of a “group” for purposes of Section 13(d) of the Exchange Act. However, the filing of this Amendment No. 1 shall not be deemed an admission that the Reporting Persons and such other persons are members of any such group. Each other party has separately made a Schedule 13D filing, if applicable, reporting its beneficial ownership of the shares of Common Stock held by it.

Any beneficial ownership of Common Stock by any of the persons listed on Schedule I of the Schedule 13D is set forth on Schedule I filed with the Schedule 13D.

(c) The Blackstone Funds sold the following shares of Common Stock pursuant to the Underwriting Agreement on November 22, 2021 at a price to the public of $8.50 per share and a net price to the Blackstone Funds of $8.2025 per share:


Seller	Number of Shares of Common Stock Sold
Blackstone Capital Partners VI-NQ L.P.		3,036,582
Blackstone Energy Family Investment Partnership SMD L.P.		305,733
BEP CTOS Holdings L.P.		3,149,642
Blackstone Energy Family Investment Partnership NQ ESC L.P.		156,378
BCP CTOS Holdings L.P.		3,109,809
Blackstone Family Investment Partnership VI-NQ ESC L.P.		15,096
Blackstone Energy Partners NQ L.P.		2,549,735

Except as set forth in this Amendment No. 1, none of the Reporting Persons has effected any transaction in shares of Common Stock during the past 60 days.

(d) To the best knowledge of the Reporting Persons, no one other than the Reporting Persons, or the partners, members, affiliates or shareholders of the Reporting Persons, has the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Common Stock reported herein as beneficially owned by the Reporting Persons.

(e) Not applicable.

Item 6.

Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer

Item 6 of the Schedule 13D is hereby amended and supplemented by adding the following information:

The information set forth in Item 4 of this Amendment No. 1 is incorporated by reference into this Item 6.

Due to the fact that the Reporting Persons no longer beneficially own more than 4.5% of the outstanding shares of Common Stock as of November 22, 2021, as of such date the Reporting Persons rights under the Stockholders Agreement have terminated. As a consequence of such termination, the Reporting Persons no longer have a right to designate a candidate for election to the Issuer’s board of directors at the next applicable stockholders meeting of the Issuer.

Item 7.

Material to be Filed as Exhibits

Item 7 of the Schedule 13D is hereby amended and supplemented by inserting the following exhibits:


Exhibit C		Underwriting Agreement, dated November 17, 2021 among the Issuer, the Selling Stockholders listed in Schedule A thereto and the Underwriters named therein (incorporated by reference to Exhibit 1.1 to the Issuer’s Current Report on Form 8-K filed with the SEC on November 22, 2021).
Exhibit D		Form of Lock-Up Agreement, dated November 17, 2021, between the Blackstone Funds and Citigroup Global Markets Inc. (incorporated by reference as Exhibit A to the Underwriting Agreement filed as Exhibit 1.1 to the Issuer’s Current Report on Form 8-K filed with the SEC on November 22, 2021).

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: November 22, 2021


BLACKSTONE ENERGY PARTNERS NQ L.P.
By: Blackstone Energy Management Associates NQ L.L.C., its general partner
By: Blackstone EMA-NQ L.L.C., its managing member

By:		/s/ Tabea Hsi
Name: Tabea Hsi
Title: Authorized Person

BEP CTOS HOLDINGS L.P.
By: Blackstone Energy Management Associates NQ L.L.C., its general partner
By: Blackstone EMA-NQ L.L.C., its managing member

By:		/s/ Tabea Hsi
Name: Tabea Hsi
Title: Authorized Person

BLACKSTONE ENERGY FAMILY INVESTMENT PARTNERSHIP SMD L.P.
By: Blackstone Family GP L.L.C., its general partner

By:		/s/ Tabea Hsi
Name: Tabea Hsi
Title: Senior Managing Director

BLACKSTONE ENERGY FAMILY INVESTMENT PARTNERSHIP NQ ESC L.P.
By: BEP Side-by-Side GP NQ L.L.C., its general partner

By:		/s/ Tabea Hsi
Name: Tabea Hsi
Title: Authorized Person

BLACKSTONE CAPITAL PARTNERS VI-NQ L.P.
By: Blackstone Management Associates VI-NQ L.L.C., its general partner
By: BMA VI-NQ L.L.C., its managing member

By:		/s/ Tabea Hsi
Name: Tabea Hsi
Title: Authorized Person

[Custom Truck One Source, Inc. – Schedule 13D/A]

BCP CTOS HOLDINGS L.P.

By: Blackstone Management Associates VI-NQ L.L.C., its general partner

By: BMA VI-NQ L.L.C., its managing member

By: /s/ Tabea Hsi

Name: Tabea Hsi

Title: Authorized Person

BLACKSTONE ENERGY MANAGEMENT ASSOCIATES NQ L.L.C.

By: Blackstone EMA-NQ L.L.C., its managing member

By: /s/ Tabea Hsi

Name: Tabea Hsi

Title: Authorized Person

BLACKSTONE EMA-NQ L.L.C.

By: /s/ Tabea Hsi

Name: Tabea Hsi

Title: Authorized Person

BLACKSTONE FAMILY GP L.L.C.

By: /s/ Tabea Hsi

Name: Tabea Hsi

Title: Senior Managing Director

BEP SIDE-BY-SIDE GP NQ L.L.C.

By: /s/ Tabea Hsi

Name: Tabea Hsi

Title: Authorized Person

BLACKSTONE MANAGEMENT ASSOCIATES VI-NQ L.L.C.

By: BMA VI-NQ L.L.C., its managing member

By: /s/ Tabea Hsi

Name: Tabea Hsi

Title: Authorized Person

BMA VI-NQ L.L.C.

By: /s/ Tabea Hsi

Name: Tabea Hsi

Title: Authorized Person

[Custom Truck One Source, Inc. – Schedule 13D/A]


BLACKSTONE FAMILY INVESTMENT PARTNERSHIP VI-NQ ESC L.P.
By: BCP VI-NQ Side-by-Side GP L.L.C., its general partner

By:		/s/ Tabea Hsi
Name: Tabea Hsi
Title: Authorized Person

BCP VI-NQ SIDE-BY-SIDE GP L.L.C.

By:		/s/ Tabea Hsi
Name: Tabea Hsi
Title: Authorized Person

BLACKSTONE HOLDINGS II L.P.
By: Blackstone Holdings I/II GP L.L.C., its general partner

By:		/s/ Tabea Hsi
Name: Tabea Hsi
Title: Senior Managing Director

BLACKSTONE HOLDINGS I/II GP L.L.C.

By:		/s/ Tabea Hsi
Name: Tabea Hsi
Title: Senior Managing Director

[Custom Truck One Source, Inc. – Schedule 13D/A]


BLACKSTONE HOLDINGS III L.P.
By: Blackstone Holdings III GP L.P., its general partner
By: Blackstone Holdings III GP Management L.L.C., its general partner

By:		/s/ Tabea Hsi
Name: Tabea Hsi
Title: Senior Managing Director

BLACKSTONE HOLDINGS III GP L.P.
By: Blackstone Holdings III GP Management L.L.C., its general partner

By:		/s/ Tabea Hsi
Name: Tabea Hsi
Title: Senior Managing Director

BLACKSTONE HOLDINGS III GP MANAGEMENT L.L.C.

By:		/s/ Tabea Hsi
Name: Tabea Hsi
Title: Senior Managing Director

BLACKSTONE INC.

By:		/s/ Tabea Hsi
Name: Tabea Hsi
Title: Senior Managing Director

BLACKSTONE GROUP MANAGEMENT L.L.C.

By:		/s/ Tabea Hsi
Name: Tabea Hsi
Title: Senior Managing Director

/s/ Stephen A. Schwarzman
Stephen A. Schwarzman

[Custom Truck One Source, Inc. – Schedule 13D/A]