Exhibit 10.4

AMENDMENT AGREEMENT

AMENDMENT AGREEMENT (this “Amendment Agreement”), dated as of July 21, 2006
between Societe Generale, New York Branch (“Party A”) and Sabine Pass LNG, L.P.
(“Party B”). All capitalized terms used herein and not otherwise defined shall
have the respective meanings provided in the ISDA Master Agreement referred to
below.

W I T N E S S E T H:

WHEREAS, Party A and Party B are parties to an ISDA Master Agreement, dated as
of February 25, 2005 (as amended, modified or supplemented from time to time,
the “Master Agreement”);

WHEREAS, Party A and Party B wish to amend the Master Agreement as herein
provided;

NOW, THEREFORE, it is agreed:

1. Part 1(i)(i) of the Schedule to the Master Agreement is hereby amended by
deleting the words “Credit Agreement dated as of February 25, 2005” and
substituting the words “First Amended and Restated Credit Agreement dated as of
July 21, 2006” in lieu thereof.

2. Part 5(e)(vi) of the Schedule to the Master Agreement is hereby amended by
deleting the word “Nominal” and substituting the word “Notional” in lieu
thereof.

3. This Amendment Agreement is limited as specified and shall not constitute a
modification, acceptance or waiver of any other provision of the Master
Agreement.

4. This Amendment Agreement may be executed in any number of counterparts and by
the different parties hereto on separate counterparts, each of which
counterparts when executed and delivered shall be an original, but all of which
shall together constitute one and the same instrument. A complete set of
counterparts shall be lodged with Party A and Party B.

5. This Amendment Agreement and the rights and obligations of the parties
hereunder shall be construed in accordance with and governed by the laws of the
State of New York (without reference to choice of law doctrine).

6. This Amendment Agreement shall become effective on the date when Party A and
Party B shall have signed a copy hereof (whether the same or different copies)
and delivered (including by way of telecopier) the same to each other.

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IN WITNESS WHEREOF, each of the parties hereto has caused a counterpart of this
Amendment Agreement to be duly executed and delivered as of the date first above
written.

 

SOCIETE GENERALE,

NEW YORK BRANCH

    SABINE PASS LNG, L.P. By:  

/s/ Leon Valera

    By:  

/s/ Graham McArthur

Name:   Leon Valera     Name:   Graham McArthur Title:   Director     Title:  
Treasurer