Ownership Submission

FORM 4

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person ^*

ECP ControlCo, LLC

2. Issuer Name and Ticker or Trading Symbol
Custom Truck One Source, Inc. [CTOS]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

_____ Director	__X__ 10% Owner
_____ Officer (give title below)	_____ Other (specify below)

(Last)

(First)

(Middle)

40 BEECHWOOD ROAD

3. Date of Earliest Transaction (Month/Day/Year)
09/05/2024

(Street)

SUMMIT,, NJ 07901

4. If Amendment, Date Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)
___ Form filed by One Reporting Person
_X_ Form filed by More than One Reporting Person

(City)

(State)

(Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	09/05/2024		S		2,354,109	D	$ 3.42 ⁽¹⁾	23,384,879	I	See footnotes ⁽²⁾ ⁽³⁾ ⁽⁴⁾ ⁽⁵⁾

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
	Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number.		SEC 1474 (9-02)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security
(Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code
(Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date
(Month/Day/Year)

7. Title and Amount of Underlying Securities
(Instr. 3 and 4)

8. Price of Derivative Security
(Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 4)

11. Nature of Indirect Beneficial Ownership
(Instr. 4)

Code

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Reporting Owners

Reporting Owner Name / Address	Relationships
Reporting Owner Name / Address	Director	10% Owner	Officer	Other
ECP ControlCo, LLC 40 BEECHWOOD ROAD SUMMIT,, NJ 07901		X
ENERGY CAPITAL PARTNERS III, LLC 40 BEECHWOOD ROAD SUMMIT,, NJ 07901		X
Energy Capital Partners GP III, LP 40 BEECHWOOD ROAD SUMMIT,, NJ 07901		X
ENERGY CAPITAL PARTNERS III, LP 40 BEECHWOOD ROAD SUMMIT,, NJ 07901		X
ENERGY CAPITAL PARTNERS III-A, LP 40 BEECHWOOD ROAD SUMMIT,, NJ 07901		X
ENERGY CAPITAL PARTNERS III-B, LP 40 BEECHWOOD ROAD SUMMIT,, NJ 07901		X
ENERGY CAPITAL PARTNERS III-C, LP 40 BEECHWOOD ROAD SUMMIT,, NJ 07901		X
ENERGY CAPITAL PARTNERS III-D, LP 40 BEECHWOOD ROAD SUMMIT,, NJ 07901		X
ENERGY CAPITAL PARTNERS GP III CO-INVESTMENT (NESCO), LLC 40 BEECHWOOD ROAD SUMMIT,, NJ 07901		X
Energy Capital Partners III (NESCO Co-Invest), LP 40 BEECHWOOD ROAD SUMMIT,, NJ 07901		X

Signatures

ECP ControlCo, LLC, By: /s/ Rahman D'Argenio, Managing Member		09/09/2024
^**Signature of Reporting Person		Date
Energy Capital Partners III, LLC, By: ECP ControlCo, LLC, its managing member, By: /s/ Rahman D'Argenio, Managing Member		09/09/2024
^**Signature of Reporting Person		Date
Energy Capital Partners GP III, LP, By: Energy Capital Partners III, LLC, its general partner, By: ECP ControlCo, LLC, its managing member, By: /s/ Rahman D'Argenio, Managing Member		09/09/2024
^**Signature of Reporting Person		Date
Energy Capital Partners III, LP, By: Energy Capital Partners GP III, LP, its general partner, By: Energy Capital Partners III, LLC, its general partner, By: ECP ControlCo, LLC, its managing member, By: /s/ Rahman D'Argenio, Managing Member		09/09/2024
^**Signature of Reporting Person		Date
Energy Capital Partners III-A, LP, By: Energy Capital Partners GP III, LP, its general partner, By: Energy Capital Partners III, LLC, its general partner, By: ECP ControlCo, LLC, its managing member, By: /s/ Rahman D'Argenio, Managing Member		09/09/2024
^**Signature of Reporting Person		Date
Energy Capital Partners III-B, LP, By: Energy Capital Partners GP III, LP, its general partner, By: Energy Capital Partners III, LLC, its general partner, By: ECP ControlCo, LLC, its managing member, By: /s/ Rahman D'Argenio, Managing Member		09/09/2024
^**Signature of Reporting Person		Date
Energy Capital Partners III-C, LP, By: Energy Capital Partners GP III, LP, its general partner, By: Energy Capital Partners III, LLC, its general partner, By: ECP ControlCo, LLC, its managing member, By: /s/ Rahman D'Argenio, Managing Member		09/09/2024
^**Signature of Reporting Person		Date
Energy Capital Partners III-D, LP, By: Energy Capital Partners GP III, LP, its general partner, By: Energy Capital Partners III, LLC, its general partner, By: ECP ControlCo, LLC, its managing member, By: /s/ Rahman D'Argenio, Managing Member		09/09/2024
^**Signature of Reporting Person		Date
Energy Capital Partners GP III Co-Investment (NESCO), LLC, By: Energy Capital Partners III, LLC, its general partner, By: ECP ControlCo, LLC, its managing member, By: /s/ Rahman D'Argenio, Managing Member		09/09/2024
^**Signature of Reporting Person		Date
Energy Capital Partners III (NESCO Co-Invest), LP, By: Energy Capital Partners GP III Co-Investment (NESCO), LLC, By: Energy Capital Partners III, LLC, By: ECP ControlCo, LLC, By: /s/ Rahman D'Argenio, Managing Member		09/09/2024
^**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $3.42 to $3.72. The reporting persons undertake to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.
(2)	Following the transactions reported herein, ECP Cardinal Holdings, LP and NESCO Holdings, LP are the record holders of 4,088,426 and 19,296,453 shares of Common Stock, respectively.
(3)	ECP ControlCo, LLC is controlled by its board of managers, which consists of Douglas Kimmelman, Peter Labbat, Tyler Reeder, Rahman D'Argenio, Raoul Hughes and Xavier Robert (together, the "ECP Managers"), all of whom collectively share the power to vote and dispose of the securities beneficially owned by ECP ControlCo, LLC. As a result of the relationships described below, each of the ECP Managers may be deemed to share beneficial ownership of the securities described herein. Each individual disclaims beneficial ownership of such securities.
(4)	ECP ControlCo, LLC is the managing member of Energy Capital Partners III, LLC, which is the general partner of (i) Energy Capital Partners GP III, LP, which is the general partner of each of Energy Capital Partners III, LP, Energy Capital Partners III-A, LP, Energy Capital Partners III-B, LP, Energy Capital Partners III-C, LP, and Energy Capital Partners III-D, LP, which are the sole members of ECP Starlight Public GP, LLC, which is the general partner of ECP Starlight Guarantor (Public), LP, and (ii) Energy Capital Partners GP III Co-Investment (NESCO), LLC, which is the general partner of Energy Capital Partners III (NESCO Co-Invest), LP.
(5)	ECP Starlight Guarantor (Public), LP and Energy Capital Partners III (NESCO Co-Invest), LP are the sole members of NESCO Holdings GP, LLC, which is the general partner of each of ECP Cardinal Holdings, LP and NESCO Holdings, LP. Each of the entities described in footnotes 4 and 5 may be deemed to share beneficial ownership of the securities held of record by ECP Cardinal Holdings, LP and NESCO Holdings, LP.
Remarks: Due to filing limitations of the electronic filing system, each of ECP Starlight Public GP, LLC, ECP Starlight Guarantor (Public), LP, NESCO Holdings GP, LLC, NESCO Holdings, LP and ECP Cardinal Holdings, LP are filing a separate Form 4.

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