Exhibit 10.68

Execution Version

SECOND AMENDMENT TO GUARANTEE AND COLLATERAL AGREEMENTS

This SECOND AMENDMENT TO GUARANTEE AND COLLATERAL AGREEMENTS (this “Amendment”) is entered into as of this 31st day of December, 2008 by Cheniere Midstream Holdings, Inc., a Delaware corporation (“Cheniere Midstream Holdings”), Sabine Pass Tug Services, LLC, a Delaware limited liability company (“Sabine Pass Tug Services”), Cheniere LNG, Inc., a Delaware corporation (“Cheniere LNG”), Cheniere LNG Terminals, Inc., a Delaware corporation (“Cheniere LNG Terminals”), Cheniere Marketing, LLC (formerly known as Cheniere Marketing, Inc.), a Delaware limited liability company (“Cheniere Marketing”), the Lenders (as defined below) signatory hereto and The Bank of New York Mellon, as collateral agent (in such capacity and together with its successors, the “Collateral Agent”). All capitalized terms used in this Amendment and not otherwise defined herein have the meanings ascribed to such terms in the Guarantee and Collateral Agreements (as defined below).

Preliminary Statements

A. Cheniere Common Units Holding, LLC, a Delaware limited liability company (the “Borrower”) has entered into that certain Credit Agreement dated as of August 15, 2008 by and among the Borrower, The Bank of New York Mellon, as administrative agent (in such capacity and together with its successors, the “Administrative Agent”), certain affiliates of the Borrower signatory thereto and the lenders party thereto from time to time (the “Lenders”) (as the same may be amended, restated, supplemented or otherwise modified from time to time, the “Credit Agreement”).

B. In connection with the Credit Agreement, Cheniere Midstream Holdings, Sabine Pass Tug Services and certain of their affiliates have entered into that certain Guarantee and Collateral Agreement (Non-Crest Entities) dated as of August 15, 2008 (as the same may be amended, restated, supplemented or otherwise modified from time to time, the “Non-LNG Entities Guarantee and Collateral Agreement”).

C. In connection with the Credit Agreement, Cheniere LNG, Cheniere LNG Terminals, Cheniere Marketing and certain of their affiliates have entered into that certain Guarantee and Collateral Agreement (Crest Entities) dated as of August 15, 2008 (as the same may be amended, restated, supplemented or otherwise modified from time to time, the “LNG Entities Guarantee and Collateral Agreement” and collectively with the Non-LNG Entities Guarantee and Collateral Agreement, the “Guarantee and Collateral Agreements”).

D. Cheniere Midstream Holdings is the sole shareholder of Cheniere LNG Services, Inc., a Delaware corporation (“Cheniere LNG Services”); and Cheniere LNG Services is the sole member of Sabine Pass Tug Services.

E. Cheniere Midstream Holdings intends to dissolve Cheniere LNG Services, and upon such dissolution Cheniere Midstream Holdings will become the sole member of Sabine Pass Tug Services.

F. The parties hereto desire to modify the Non-LNG Entities Guarantee and Collateral Agreement so that Cheniere Midstream Holdings shall grant to the Collateral Agent (for the ratable benefit of the Secured Parties) a security interest in the in the membership interests in Sabine Pass Tug Services.

G. Cheniere LNG Terminals is the sole member of Cheniere Marketing.

H. Cheniere LNG Terminals intends to transfer one percent (1%) of the membership interests in Cheniere Marketing to Cheniere LNG.

I. The parties hereto desire to modify the LNG Entities Guarantee and Collateral Agreement so that Cheniere LNG shall grant to the Collateral Agent (for the ratable benefit of the Secured Parties) a security interest in the membership interests owned by it in Cheniere Marketing.

NOW THEREFORE, in consideration of the premises and other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, Cheniere Midstream Holdings, Sabine Pass Tug Services, Cheniere LNG Terminals, Cheniere LNG, Cheniere Marketing (collectively, the “Cheniere Parties”), the Administrative Agent, the Collateral Agent and the Required Lenders hereby agree as follows:

Notwithstanding anything to the contrary in this Amendment, each Lender by delivering its signature page to this Amendment shall be deemed to have acknowledged receipt of and consented to and approved the Amendment and each other document required to be approved by any Agent or any Lender, as applicable, on the date such Lender delivers its signature to this Amendment and the Administrative Agent shall be entitled to rely on such confirmation.

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SCHEDULE 4.07(a) TO GUARANTEE AND COLLATERAL AGREEMENT

(NON-CREST ENTITIES)

DESCRIPTION OF PLEDGED EQUITY INTERESTS

SCHEDULE 4.07(a) TO GUARANTEE AND COLLATERAL AGREEMENT

(CREST ENTITIES)

DESCRIPTION OF PLEDGED EQUITY INTERESTS