SECURITIES AND EXCHANGE COMMISSION	 	
 	Washington, D.C. 20549	 	

 
SCHEDULE 13G
 
(Rule 13d-102)
 
SUMMIT MIDSTREAM PARTNERS, LP
(Name of Issuer)
COMMON UNITS REPRESENTING LIMITED PARTNER INTERESTS
(Title of Class of Securities)
866142102
(CUSIP Number)
DECEMBER 31, 2012
(Date of Event Which Requires Filing of this Statement)
Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
o	Rule 13d-1(b)	
o	Rule 13d-1(c)	
x	Rule 13d-1(d)	
 
*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 the disclosures provided in a prior cover page.
 
The information required in 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.: 866142102	SCHEDULE 13G	 	 	
 	 	
 	1	Names of Reporting Persons
Summit Midstream Partners LLC	 	
 	 	
 	2	Check the Appropriate Box if a Member of a Group (See Instructions)	 	
 	 	(a)	o	 	
 	 	(b)	o	 	
 	 	
 	3	SEC Use Only	 	
 	 	
 	4	Citizenship or Place of Organization
Delaware	 	
 	 	 	 	
Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With:	5	Sole Voting Power
34,439,700(1)	 	
 	 	 	 	 	 	
 	6	Shared Voting Power

 	 	 	 	 	 	 	 	 	 	 	 	
 	7	Sole Dispositive Power
34,439,700(1)	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	8	Shared Dispositive Power

 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	9	Aggregate Amount Beneficially Owned by Each Reporting Person
34,439,700(1)	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	10	Check Box if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) o	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	11	Percent of Class Represented by Amount in Row (9)
70.5%(2)	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	12	Type of Reporting Person (See Instructions)
OO (limited liability company)	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	

(1)       Includes 10,029,850 common units representing limited partner interests (“Common Units”) and 24,409,850 subordinated units representing limited partner interests (“Subordinated Units”) in the Issuer held directly by the Reporting Person. The Subordinated Units may be converted into Common Units on a one-for-one basis after expiration of the subordination period (as defined in the Issuer’s First Amended and Restated Agreement of Limited Partnership (the “Partnership Agreement”), which is incorporated by reference herein), and other circumstances as noted in the Partnership Agreement. As such Subordinated Units were acquired in connection with transactions having the effect of changing or influencing the control of the Issuer, such Subordinated Units are considered converted for purposes of the calculations of the amounts noted under Rule 13d-3(d)(1)(i) of the Securities Exchange Act of 1934, as amended.
 
(2)       Based upon 24,409,850 Common Units and 24,409,850 Subordinated Units outstanding as of October 31, 2012, as reported in the Issuer’s most recent Form 10-Q filed on November 14, 2012.
 
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CUSIP No.: 866142102	SCHEDULE 13G	 	 	
 	 	
 	1	Names of Reporting Persons
Energy Capital Partners II, LLC	 	
 	 	
 	2	Check the Appropriate Box if a Member of a Group (See Instructions)	 	
 	 	(a)	o	 	
 	 	(b)	o	 	
 	 	
 	3	SEC Use Only	 	
 	 	
 	4	Citizenship or Place of Organization
Delaware	 	
 	 	 	 	
Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With:	5	Sole Voting Power

 	 	 	 	 	 	
 	6	Shared Voting Power
34,439,700(1)	 	 	 	 	 	 	 	
 	 	 	 	 	 	 	 	 	 	 	 	
 	7	Sole Dispositive Power

 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	8	Shared Dispositive Power
34,439,700(1)	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	9	Aggregate Amount Beneficially Owned by Each Reporting Person
34,439,700(1)	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	10	Check Box if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) o	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	11	Percent of Class Represented by Amount in Row (9)
70.5%(2)	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	
 	12	Type of Reporting Person (See Instructions)
OO (limited liability company)	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	

(1)        Summit Midstream Partners LLC (“Summit Investments”) owns 10,029,850 common units representing limited partner interests (“Common Units”) and 24,409,850 subordinated units representing limited partner interests (“Subordinated Units”) in the Issuer. Energy Capital Partners II, LLC (“ECP II”) and its parallel and co-investment funds (the “ECP Funds” and, together with ECP II, “ECP”) hold, in the aggregate, an approximate 90.6% ownership interest in Summit Investments. ECP II is the general partner of the general partner of each ECP Fund that holds membership interests in Summit Investments and has voting and investment control over the securities held thereby. Accordingly, ECP may be deemed to indirectly beneficially own the Common Units and the Subordinated Units of the Issuer held by Summit Investments. The Subordinated Units may be converted into Common Units on a one-for-one basis after expiration of the subordination period (as defined in the Issuer’s First Amended and Restated Agreement of Limited Partnership (the “Partnership Agreement”), which is incorporated by reference herein), and other circumstances as noted in the Partnership Agreement. As such Subordinated Units were acquired in connection with transactions having the effect of changing or influencing the control of the Issuer, such Subordinated Units are considered converted for purposes of the calculations of the amounts noted under Rule 13d-3(d)(1)(i) of the Securities Exchange Act of 1934, as amended.
 
(2)        Based upon 24,409,850 Common Units and 24,409,850 Subordinated Units outstanding as of October 31, 2012, as reported in the Issuer’s most recent Form 10-Q filed on November 14, 2012.
 
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CUSIP No.: 866142102	SCHEDULE 13G	 	
 	
Item 1(a).	Name of Issuer:
Summit Midstream Partners, LP	
Item 1(b).	Address of Issuer’s Principal Executive Offices:
2100 McKinney Avenue, Suite 2150
Dallas, Texas 75201	
 	
Item 2(a).	Name of Person(s) Filing:
Summit Midstream Partners LLC
Energy Capital Partners II, LLC	 
(“Summit Investments”)
(“ECP II”)	
Item 2(b).	Address of Principal Business Office or, if none, Residence:
Principal business office for Summit Investments:
 
2100 McKinney Avenue, Suite 2150
Dallas, Texas 75201
 
Principal business office for ECP II:
 
51 John F. Kennedy Parkway, Suite 200
Short Hills, New Jersey 07078	
Item 2(c).	Citizenship:
Summit Investments
ECP	 
Delaware
Delaware	
Item 2(d).	Title of Class of Securities:
Common units representing limited partner interests	
Item 2(e).	CUSIP Number:
866142102	
 	
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:	
 	Not applicable.	

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CUSIP No.: 866142102	SCHEDULE 13G	 	
 	
Item 4.	Ownership:	
Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.	

 	 	 	Summit
Investments	 	ECP II	 	
(a)	Amount beneficially owned:	 	34,439,700	(1)(2)	34,439,700	(2)(3)	
(b)	Percent of class:	 	70.5	% (4)	70.5	% (4)	
(c)	Number of shares as to which such person has:	 	 	 	 	 	
 	(i) Sole power to vote or to direct the vote:	 	34,439,700	(1)	 	 	
 	(ii) Shared power to vote or to direct the vote:	 	 	 	34,439,700	(3)	
 	(iii) Sole power to dispose or to direct the disposition of:	 	34,439,700	(1)	 	 	
 	(iv) Shared power to dispose or to direct the disposition of:	 	 	 	34,439,700	(3)	

(1)   Includes 10,029,850 common units representing limited partner interests (“Common Units”) and 24,409,850 subordinated units representing limited partner interests (“Subordinated Units”) in the Issuer held directly by Summit Investments.
 
(2)   The Subordinated Units may be converted into Common Units on a one-for-one basis after expiration of the subordination period (as defined in the Issuer’s First Amended and Restated Agreement of Limited Partnership (the “Partnership Agreement”), which is incorporated by reference herein), and other circumstances as noted in the Partnership Agreement.
 
(3)   Summit Investments beneficially owns 10,029,850 Common Units and 24,409,850 Subordinated Units in the Issuer. ECP II and its parallel and co-investment funds (the “ECP Funds” and, together with ECP II, “ECP”) hold, in the aggregate, an approximate 90.6% ownership interest in Summit Investments. ECP II is the general partner of the general partner of each ECP Fund that holds membership interests in Summit Investments and has voting and investment control over the securities held thereby. Accordingly, ECP may be deemed to indirectly beneficially own the 10,029,850 Common Units and the 24,409,850 Subordinated Units of the Issuer held by Summit Investments.
 
(4)   Based upon 24,409,850 Common Units and 24,409,850 Subordinated Units outstanding as of October 31, 2012, as reported in the Issuer’s most recent Form 10-Q filed on November 14, 2012.
 	
Item 5.	Ownership of Five Percent or Less of a Class:	
If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following:   o   Not applicable.	
 	
Item 6.	Ownership of More than Five Percent on Behalf of Another Person:	
Not applicable.	
 	
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person:	
Not applicable.	
 	
Item 8.	Identification and Classification of Members of the Group:	
Not applicable.	
 	
Item 9.	Notice of Dissolution of Group:	
Not applicable.	
 	
Item 10.	Certification:	
Not applicable.	
 
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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: February 19, 2013	 	

 	SUMMIT MIDSTREAM PARTNERS LLC	
 	a Delaware limited liability company	

 	By:	/s/ Brock M. Degeyter	
 	 	Brock M. Degeyter	
 	 	Vice President, General Counsel and Secretary	

 	ENERGY CAPITAL PARTNERS II, LLC	
 	a Delaware limited liability company	

 	By:	/s/ Christopher M. Leininger	
 	 	Christopher M. Leininger	
 	 	Deputy General Counsel	
 
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JOINT FILING AGREEMENT
 
In accordance with Rule 13(d)-1(k)(1) under the Securities Exchange Act of 1934, as amended, the undersigned hereby agree to the joint filing with each other of the attached statement on Schedule 13G and to all amendments to such statement.
 
IN WITNESS WHEREOF, the undersigned hereby executed this Agreement as of February 19, 2013.

 	SUMMIT MIDSTREAM PARTNERS LLC	
 	a Delaware limited liability company	

 	By:	/s/ Brock M. Degeyter	
 	 	Brock M. Degeyter	
 	 	Vice President, General Counsel and Secretary	

 	ENERGY CAPITAL PARTNERS II, LLC	
 	a Delaware limited liability company	

 	By:	/s/ Christopher M. Leininger	
 	 	Christopher M. Leininger	
 	 	Deputy General Counsel	
 
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