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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Name of Issuer)

(Title of Class of Securities)

(CUSIP Number)

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

SCHEDULE 13D/A 0001213900-19-014817 0001707921 XXXXXXXX LIVE 7 Common Stock 12/19/2024 false 0001709682 23204X103 Custom Truck One Source, Inc. 7701 INDEPENDENCE AVENUE KANSAS CITY KANSAS CITY MO 64125 Christopher M. Leininger, Esq. (973) 671-6100 7701 INDEPENDENCE AVENUE KANSAS CITY KANSAS CITY MO 64125 0001707921 N ECP ControlCo, LLC OO N DE 0.00 16287270.00 0.00 16287270.00 16287270.00 N 7.0 OO Limited Liability Company Y Energy Capital Partners III, LLC OO N DE 0.00 16287270.00 0.00 16287270.00 16287270.00 N 7.0 OO Limited Liability Company Y Energy Capital Partners GP III, LP OO N DE 0.00 16287270.00 0.00 16287270.00 16287270.00 N 7.0 PN Y Energy Capital Partners III, LP OO N DE 0.00 16287270.00 0.00 16287270.00 16287270.00 N 7.0 PN Y Energy Capital Partners III-A, LP OO N DE 0.00 16287270.00 0.00 16287270.00 16287270.00 N 7.0 PN Y Energy Capital Partners III-B, LP OO N DE 0.00 16287270.00 0.00 16287270.00 16287270.00 N 7.0 PN Y Energy Capital Partners III-C, LP OO N DE 0.00 16287270.00 0.00 16287270.00 16287270.00 N 7.0 PN Y Energy Capital Partners III-D, LP OO N DE 0.00 16287270.00 0.00 16287270.00 16287270.00 N 7.0 PN Y Energy Capital Partners GP III Co-Investment (NESCO), LLC OO N DE 0.00 16287270.00 0.00 16287270.00 16287270.00 N 7.0 OO Limited Liability Company Y Energy Capital Partners III (NESCO Co-Invest), LP OO N DE 0.00 16287270.00 0.00 16287270.00 16287270.00 N 7.0 PN Y ECP Starlight Public GP, LLC OO N DE 0.00 16287270.00 0.00 16287270.00 16287270.00 N 7.0 OO Limited Liability Company Y ECP Starlight Guarantor (Public), LP OO N DE 0.00 16287270.00 0.00 16287270.00 16287270.00 N 7.0 PN Y NESCO Holdings GP, LLC OO N DE 0.00 16287270.00 0.00 16287270.00 16287270.00 N 7.0 OO Limited Liability Company Y NESCO Holdings, LP OO N DE 0.00 13439824.00 0.00 13439824.00 13439824.00 N 5.8 PN Y ECP Cardinal Holdings, LP OO N DE 0.00 2847446.00 0.00 2847446.00 2847446.00 N 1.2 PN Common Stock Custom Truck One Source, Inc. 7701 INDEPENDENCE AVENUE KANSAS CITY KANSAS CITY MO 64125 The information set forth on the cover pages of this Schedule 13D is hereby incorporated by reference in this Item 5(a) and (b). The following sets forth, as of the date of this Statement, the aggregate number of shares of Common Stock and percentage of shares of Common Stock beneficially owned by each of the Reporting Persons, as well as the number of shares of Common Stock as to which each Reporting Person has the 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 of, or shared power to dispose or to direct the disposition of, as of the date hereof, based on 233,432,467 shares of Common Stock outstanding as of October 28, 2024, as disclosed in the Issuer's Quarterly Report on Form 10-Q as filed with the Securities and Exchange Commission on October 30, 2024. -ECP Cardinal Holdings, LP -- Amount beneficially owned: 2,847,446 -- Percent of Class: 1.2% -- Sole power to vote or to direct the vote: 0 -- Shared power to vote or to direct the vote: 2,847,446 -- Sole power to dispose or to direct the disposition: 0 -- Shared power to dispose or to direct the disposition: 2,847,446 -NESCO Holdings, LP -- Amount beneficially owned: 13,439,824 -- Percent of Class: 5.8% -- Sole power to vote or to direct the vote: 0 -- Shared power to vote or to direct the vote: 13,439,824 -- Sole power to dispose or to direct the disposition: 0 -- Shared power to dispose or to direct the disposition: 13,439,824 -Each of the other Reporting Persons: -- Amount beneficially owned: 16,287,270 -- Percent of Class: 7.0% -- Sole power to vote or to direct the vote: 0 -- Shared power to vote or to direct the vote: 16,287,270 -- Sole power to dispose or to direct the disposition: 0 -- Shared power to dispose or to direct the disposition: 16,287,270 ECP Cardinal Holdings, LP and NESCO Holdings, LP are the record holders of 2,847,446 and 13,439,824 shares of Common Stock, respectively. 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. 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. 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 foregoing entities may be deemed to share beneficial ownership of the securities held of record by ECP Cardinal Holdings, LP and NESCO Holdings, LP. See Item 5(a) above. On December 19, 2024, ECP Cardinal Holdings, LP and NESCO Holdings, LP disposed of 699,306 and 3,300,694 shares of Common Stock, respectively, in a block trade at a price of $4.40 per share. None. Not applicable. ECP ControlCo, LLC /s/ Rahman D'Argenio Rahman D'Argenio Managing Member 12/23/2024 Energy Capital Partners III, LLC ECP ControlCo, LLC, its managing member /s/ Rahman D'Argenio Rahman D'Argenio Managing Member 12/23/2024 Energy Capital Partners GP III, LP Energy Capital Partners III, LLC, its general partner ECP ControlCo, LLC, its managing member /s/ Rahman D'Argenio Rahman D'Argenio Managing Member 12/23/2024 Energy Capital Partners III, LP Energy Capital Partners GP III, LP, its general partner Energy Capital Partners III, LLC, its general partner ECP ControlCo, LLC, its managing member Rahman D'Argenio Managing Member 12/23/2024 Energy Capital Partners III-A, LP Energy Capital Partners GP III, LP, its general partner Energy Capital Partners III, LLC, its general partner ECP ControlCo, LLC, its managing member Rahman D'Argenio Managing Member 12/23/2024 Energy Capital Partners III-B, LP Energy Capital Partners GP III, LP, its general partner Energy Capital Partners III, LLC, its general partner ECP ControlCo, LLC, its managing member Rahman D'Argenio Managing Member 12/23/2024 Energy Capital Partners III-C, LP Energy Capital Partners GP III, LP, its general partner Energy Capital Partners III, LLC, its general partner ECP ControlCo, LLC, its managing member Rahman D'Argenio Managing Member 12/23/2024 Energy Capital Partners III-D, LP Energy Capital Partners GP III, LP, its general partner Energy Capital Partners III, LLC, its general partner ECP ControlCo, LLC, its managing member Rahman D'Argenio Managing Member 12/23/2024 Energy Capital Partners GP III Co-Investment (NESCO), LLC Energy Capital Partners III, LLC, its general partner ECP ControlCo, LLC, its managing member /s/ Rahman D'Argenio Rahman D'Argenio Managing Member 12/23/2024 Energy Capital Partners III (NESCO Co-Invest), LP Energy Capital Partners GP III Co-Investment (NESCO), LLC Energy Capital Partners III, LLC, its general partner ECP ControlCo, LLC, its managing membe Rahman D'Argenio Managing Member 12/23/2024 ECP Starlight Public GP, LLC /s/ Christopher M. Leininger Christopher M. Leininger Executive Vice President & General Counsel 12/23/2024 ECP Starlight Guarantor (Public), LP ECP Starlight Public GP, LLC, its general partner /s/ Christopher M. Leininger Christopher M. Leininger Executive Vice President & General Counsel 12/23/2024 NESCO Holdings GP, LLC /s/ Rahman D'Argenio Rahman D'Argenio President 12/23/2024 NESCO Holdings, LP NESCO Holdings GP, LLC, its general partner /s/ Rahman D'Argenio Rahman D'Argenio President 12/23/2024 ECP Cardinal Holdings, LP NESCO Holdings GP, LLC, its general partner /s/ Rahman D'Argenio Rahman D'Argenio President 12/23/2024