THIRD AMENDMENT TO PARENT COMPANY AGREEMENT

Exhibit 10.1

THIRD AMENDMENT

TO

PARENT COMPANY AGREEMENT

This Third Amendment to Parent Company Agreement (this “Amendment”), dated as of July 29, 2004, is entered into by and among Duke Energy Field Services Corporation, a Delaware corporation (“DEFS Holding”), Duke Energy Field Services, LLC, a Delaware limited liability company (the “Company”), ConocoPhillips Company, a Delaware corporation (“COP”) and Duke Energy Corporation, a North Carolina corporation (“Duke”).

WHEREAS, reference is made to that certain Parent Company Agreement by and among the Company, DEFS Holding, COP and Duke dated as of March 31, 2000, as amended by the First Amendment to Parent Company Agreement dated as of May 25, 2000 and as further amended by the Second Amendment to Parent Company Agreement dated as of August 4, 2000 (as so amended the “Parent Company Agreement”) (capitalized terms used but not defined herein shall have the meaning given thereto in the Parent Company Agreement); and

WHEREAS, the parties desire to amend the Parent Company Agreement as set forth herein.

NOW, THEREFORE, for and in consideration of the mutual benefits to be derived from this Amendment, and intending to be legally bound hereby, the parties hereto hereby agree as follows:

(a) Section 5.1 of the Parent Company Agreement is hereby amended by deleting Section 5.1 thereof and replacing it with the following in its place and stead:

“Section 5.1 Structure; Transfers. For the period from the date of this Agreement until the consummation of the IPO, (i) Duke shall cause DEFS Holding to own and hold all of Duke’s Company Interest, and (ii) Phillips shall cause (A) PGC to own and hold all of Phillips’ Company Interest and no other assets or liabilities and (B) PGCSI to own and hold all of the capital stock of PGC and no other assets or liabilities.”

(b) Article V of the Parent Company Agreement is hereby amended by adding at the end of such Article the following new Section:

“Section 5.4 Indemnity. Duke shall indemnify and hold harmless COP and its Affiliates and the Company and its Affiliates (excluding Duke and Duke’s Subsidiaries other than the Company and the Company’s Subsidiaries) from and against the present value tax cost incurred by COP and its Affiliates and the Company and its Affiliates (excluding Duke and Duke’s Subsidiaries other than the Company and the Company’s

Subsidiaries) in connection with any tax depreciation restart liability that COP and its Affiliates may incur as a result of the restructuring or reorganization of the Company by Duke if an IPO is consummated in the structure originally contemplated by Duke and COP on the Closing Date.”

IN WITNESS WHEREOF, each of the undersigned, intending to be legally bound, has caused this Amendment to be duly executed and delivered on the date first set forth above.

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