UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

AMENDMENT NO. 2

to

SCHEDULE TO

Tender Offer Statement under Section 14(d)(1) or 13(e)(1)

of the Securities Exchange Act of 1934

Summit Midstream Partners, LP

(Name of Subject Company and Filing Person (Issuer))

9.50% Series A Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Units

(Title of Class of Securities)

866142AA0

(CUSIP Number of Class of Securities)

James D. Johnston

910 Louisiana Street, Suite 4200

Houston, Texas 77002

(832) 413-4770

(Name, address and telephone number of person authorized to receive notices and communications on behalf of filing person)

Copies to:

Joshua Davidson

Clinton W. Rancher

Baker Botts L.L.P.

910 Louisiana Street

Houston, Texas 77002

(713) 229-1234

CALCULATION OF FILING FEE

Check the appropriate boxes below to designate any transactions to which the statement relates:

Check the following box if the filing is a final amendment reporting the results of the tender offer:  ☐

If applicable, check the appropriate box(es) below to designate the appropriate rule provision(s) relied upon:

INTRODUCTORY STATEMENT

This Amendment No. 2 amends and supplements the Tender Offer Statement on Schedule TO (the “Schedule TO”) originally filed with the Securities and Exchange Commission on March 10, 2021 by Summit Midstream Partners, LP (the “Partnership”), as amended by the Amendment No. 1 to Schedule TO filed on March 16, 2021 (“Amendment No. 1”), in connection with its offer to exchange, on the terms and subject to the conditions set forth in the Offer to Exchange, dated March 10, 2021 (as it may be supplemented and amended from time to time, the “Offer to Exchange”), and the related Letter of Transmittal (as it may be supplemented and amended from time to time, the “Letter of Transmittal” and, together with the Offer to Exchange, the “Offering Documents”), the Partnership’s 9.50% Series A Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Units (Liquidation Preference $1,000) (the “Series A Preferred Units”) tendered in the Exchange Offer for up to 2,160,000 newly issued common units (the “Maximum Exchange Amount”) representing limited partner interests in the Partnership (the “Common Units”).

This Amendment No. 2 is being filed to reflect an increase of the exchange consideration and the Maximum Exchange Amount. For each Series A Preferred Unit properly tendered (and not validly withdrawn) prior to 11:59 p.m., New York City time, on April 6, 2021 (such time and date, as the same may be extended, the “Expiration Date”) and accepted by the Partnership, participating holders of Series A Preferred Units will receive 30 Common Units for each Series A Preferred Unit properly tendered, which is an increase of three Common Units, or approximately 11% more than the previous offer of 27 Common Units for each Series A Preferred Unit properly tendered (and not validly withdrawn). Further, the Maximum Exchange Amount will be increased from 2,160,000 Common Units to 2,400,000 Common Units to reflect the increased exchange consideration. Except as specifically provided herein and in Amendment No. 1, the information contained in the Offering Documents remains unchanged by this Amendment No. 2. You should read this Amendment No. 2 together with the Offering Documents and Amendment No. 1. Capitalized terms used but not defined herein shall have the meanings given to them in the Offer to Exchange.

Items 1 through 9 and Item 11.

Amendments to the Offer to Exchange

Amendments to the Letter of Transmittal

1

Item 7. Source and Amount of Funds or Other Consideration.

Section (a) of Item 7 of the Schedule TO is hereby amended and restated as follows:

The information set forth in the Offer to Exchange in the sections titled “The Exchange Offer — Terms of the Exchange Offer” and “Questions and Answers About the Exchange Offer” are incorporated herein by reference. Assuming full participation in the Exchange Offer, the Partnership will issue 2,400,000 Common Units as consideration for the Exchange Offer.

Item 12. Exhibits.

2

Item 13. Information Required by Schedule 13E-3.

Not applicable.

3

SIGNATURES

After due 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.

Date: March 23, 2021

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