SIXTH AMENDMENT TO GAS SALES AGREEMENT

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Exhibit 10.99

SIXTH AMENDMENT TO
GAS SALES AGREEMENT

        This Sixth Amendment to Gas Sales Agreement ("Amendment") is executed as of December 31, 2004, by Tipperary Oil & Gas (Australia) Pty Ltd (ACN 077 536 871) of GPO Box 1100, Brisbane, Queensland, Australia 4001 ("Seller"), and QUEENSLAND FERTILISER ASSETS LIMITED (ACN 011 062 294) of 76 Arthur Street, Roma, Queensland, Australia ("Buyer").

WITNESSETH:

A.

The Seller and Buyer have previously delivered Gas Sales Agreement dated September 28, 2001, as amended by Amendment to Gas Sales Agreement dated as of May 30, 2002, Second Amendment to Gas Sale Agreement dated as of September 1, 2002, Third Amendment to Gas Sale Agreement dated as of January 1, 2003, Fourth Amendment to Gas Sale Agreement dated as of March 31, 2003 and Fifth Amendment to Gas Sale Agreement dated as of June 30, 2003 (collectively, the "Original Agreement") governing the sale and supply of Gas to Buyer subject to the terms and conditions set forth therein including, without limitation, the Seller and the Buyer obtaining necessary financing commitments, under terms reasonably acceptable to each of them, by December 31, 2003 for (a) Buyer to construct and commission the Plant and the Pipeline between December 31, 2003 and the Commencement Date and (b) Seller to drill and complete the number of wells, and install laterals and compressors, as Seller reasonably deems necessary between December 31, 2003 and the Commencement Date to deliver the ACQ to the Delivery Point and meet Pipeline Pressure requirements; and

B.

The Seller and Buyer have agreed, subject to the terms and conditions set forth below, to amend the Original Agreement to (1) extend the date for Seller and Buyer to obtain their respective financing commitments to March 31, 2004 and (2) otherwise modify the Original Agreement as set forth herein .

        NOW, THEREFORE, for a sufficient consideration received by each, the Seller and Buyer agree to amend the Original Agreement as follows.

1.

Definitions . The definition of Commencement Date in the Original Agreement is hereby amended and replaced in its entirety as set forth below.

        "Commencement Date" means the later of:

(a)

1 September 2006; or

(b)

the date after 1 September 2006 on which the Buyer takes the first delivery of Gas from the Seller under this Agreement pursuant to the notice given under Clause 2.4 ;

         provided that , if Buyer has not previously taken the first delivery of Gas from the Seller under Subparagraph (b) above, the Commencement Date shall be deemed to occur on 1 January 2007."

2.

Sale and Purchase . Section 2.1, the preamble of Section 2.2 and Section 2.4 of the Original Agreement, each stating conditions precedent to Seller's and Buyer's obligations under the Original Agreement, are hereby amended and replaced in their entirety as set forth below.

"2.1 The obligations of the Parties under the Agreement, other than their obligations under Clauses 17, 20 and 24 , are subject to and do not become binding unless:

(a)

Buyer: (i) establishes and maintains its creditworthiness to the reasonable satisfaction of the Seller, and (ii) the Buyer has in place the necessary financing commitments, under terms

1

reasonably acceptable to Buyer and Seller, that will foreseeably allow Buyer to construct and commission the Plant and the Pipeline between March 31, 2004 and the Commencement Date. If these conditions precedent are not satisfied by March 31, 2004, then this Agreement will terminate (except for Clauses 17, 20 and 24 and the enforcement of any right or claim which arises thereunder), unless the Seller agrees in writing to extend the time required to meet these conditions.

(b)

Seller has in place the ne