Exhibit 10.7 Amendment to Pre-Acquisition Agreement


    
      

    

     

    

      


      


      Amendment
        to Pre-Acquisition Agreement

      


      This
        Amendment to Pre-Acquisition Agreement
        (the
“Amendment”)
        is
        made effective as of May 20,
        2005,
        among Enterra Energy Trust, an open-ended unincorporated trust governed by
        the
        laws of the Province of Alberta and having an office in the City of Calgary,
        Alberta (hereinafter called “Enterra”);
        Rocky
        Mountain Gas, Inc., a body corporate incorporated under the laws of the State
        of
        Wyoming and having an office in the City of Riverton, Wyoming (hereinafter
        called “RMG”);
        U.S.
        Energy Corp., a body corporate incorporated under the laws of the State of
        Wyoming and having an office in the City of Riverton, Wyoming (hereinafter
        called “USE”); and Crested Corp., a body corporate incorporated under the laws
        of the State of Wyoming and having an office in the City of Riverton, Wyoming
        (hereinafter called “Crested”).
        Together, Enterra, RMG, USE and Crested are sometimes referred to herein
        as the
“parties.”
        

      


      Terms
        not
        defined in this Amendment have the meanings defined in the Pre-Acquisition
        Agreement (the “Agreement”).
         

      


      Whereas:

      


      A.  The
        parties have signed the “Agreement” dated February 22, 2005

      


      -  and
        -


      


      B.  The
        parties by this Amendment wish to change certain provisions of the
        Agreement

      


      Now
        Therefore in Consideration of
        the
        mutual covenants hereinafter set out, and of the mutual covenants set out
        in the
        Agreement, the parties hereby agree that the following sections of the Agreement
        (all of which is incorporated herein by reference) are amended as
        follows:

      


      	1.1.2  	
              $6,000,002
                of the consideration shall be paid by the Deposit ($500,000) and
                289,474
                Trust Units ($5,500,002 at $19.00 per Trust Unit). The number of
                Initial
                Units to be issued on consummation of the Share Exchange Plan shall
                be
                reduced for the difference between $266,000 and the amount USE pays
                to
                purchase the overriding royalty interests (hereafter referred to
                as the
                “Initial
                Units”).
                

            


      


      	1.1.8  	
              Clause
                (i) is clarified to state that “the completion of the Share Exchange Plan
                (to be the day on which articles of share exchange are filed with
                the
                Wyoming Secretary of State, which articles shall be transmitted to
                the
                Secretary of State on the day of the Meeting, for filing on the calendar
                day following the Meeting).” The date in clause (iii) is changed to be
                June 1, 2005. The second sentence is changed to read “Subject to the
                satisfaction or waiver of the conditions set forth in Schedule “A” hereto,
                Enterra will take up and pay for all RMG Shares on June 1, 2005.”
                

            


      


      	1.1.5  	
              Initial
                Units is substituted for “cash.” The number of Initial Units which
                otherwise would be issued to USE based on its percentage ownership
                of RMG
                Shares shall be reduced by 26,316 (equal to $500,000 divided by $19.00).
                USE may pay off some of the Geddes Loan by transfer to Geddes and
                Company
                of a portion of the Initial Units which USE shall receive for its
                RMG
                Shares, subject to receipt by Enterra of applicable representations
                and
                warranties by Geddes.

            



      
        
           

          
          

        

        
          
          

          
            

          

        

        
          
          

        

      


      


      	1.1.10  	
              An
                extension of the Offer past June 1, 2005 will be deemed a change
                adverse
                to the Shareholders.

            


      


      	1.7  	
              Changed
                to read “Prior to June 1, 2005, USE shall have obtained the agreement of
                Geddes and Company (and Enterra shall have approved of the form of
                such
                agreement) that the collateral security for the Geddes Loan consisting
                of
                4,333,333 RMG Shares held by USE and security in RMG’s interests in the
                Castle Rock area mineral leases shall be placed into an independent
                escrow, and such RMG Shares and security interests in the Castle
                Rock area
                mineral leases (and releases for the other collateral securing the
                Geddes
                Loan) shall be released (and the certificate for the 4,333,333 RMG
                Shares
                and releases on the leases delivered to Enterra), and the Geddes
                Conversion Option shall have been terminated, and the warrants to
                purchase
                RMG common stock held by Geddes shall have been exercised (and all
                of the
                warrant shares shall be immediately cancelled and terminated on the
                date
                of completion of the Share Exchange Plan.

            


      


      Schedule
        “B” The
        second sentence of paragraph (3) is changed to read “Prior to June 1, 2005, USE
        shall have obtained the agreement of Geddes and Company (and Enterra shall
        have
        approved of the form of such agreement) that the collateral security for
        the
        Geddes Loan consisting of 4,333,333 RMG Shares held by USE and security in
        RMG’s
        interests in the Castle Rock area mineral leases shall be placed into an
        independent escrow, and such RMG Shares and security interests in the Castle
        Rock area mineral leases (and releases for the other collateral securing
        the
        Geddes Loan) shall be released (and the certificate for the 4,333,333 RMG
        Shares
        and releases on the leases delivered to Enterra), and the Geddes Conversion
        Option shall have been terminated, and the warrants to purchase RMG common
        stock
        held by Geddes shall have been exercised (and all of the warrant shares shall
        be
        immediately cancelled and terminated) on the date of completion of the Share
        Exchange Plan ”

      


      
        	 	
                 

              	
                Paragraphs
                  (16)(a), 16(e) and 16(f) as to tax matters has been modified, clarified
                  and amended pursuant to the May 5, 2005 letter to Enterra regarding
                  such
                  matters. 

              


      

      


      Schedule
        “C” Paragraphs
        (3) and (6) are deleted. A new paragraph (7) is added: “7.
        No TSX Hold Period on Initial Units; U.S. Restriction on Re-sales; Covenant
        to
        Instruct Transfer Agent to Remove U.S. Restrictive Legend on Compliance with
        Rule 904.
        The
        Initial Units shall be immediately tradable on the Toronto Stock Exchange.
        The
        Initial Units shall be issued as ‘restricted securities’ under SEC Rule 144, and
        therefore will not be tradable on Nasdaq or otherwise disposed of in the
        United
        States except in compliance with U.S. federal and state securities laws.
        Enterra
        covenants that it shall issue instructions to the transfer agent for the
        Trust
        Units to the effect that the U.S. restrictive legend (to be imprinted on
        the
        certificates for the Trust Units) will be removed upon presentation to the
        transfer agent of the seller’s compliance with SEC rule 904.” Enterra covenants
        that if it files a registration statement with the SEC for re-sale of Trust
        Units at any time before the second anniversary of consummation of the Share
        Exchange Plan, and Enterra determines in good faith that it is commercially
        reasonable for Enterra to include therein (on a piggy-back basis) such of
        the
        Initial Units as then are held by the (then-former) RMG Shareholders, Enterra
        shall include such Initial 

       

       

      
        
           

        

        
          2

          
            

          

        

        
           

        

      

       

      Units
        in
        the registration statement and name the (then-former) RMG Shareholders as
        sellers, all at Enterra’s sole expense (other than taxes and brokerage fees
        which shall be borne by the securityholder). Notwithstanding the foregoing,
        if
        any holder of Initial Units can sell all of such units pursuant to Rule 144
        in
        any three-month period, Enterra need not include such securityholder in the
        registration statement. 

      


      Except
        as
        changed by this Amendment, the Agreement remains in full force and
        effect.

      


      


      In
        Witness Whereof
        the
        parties hereto have caused this Amendment to be executed on their behalf
        by
        their officers thereunto duly authorized on May 20,
        2005
        and effective as of that date.

       

      

        
          	 	 	
                  ENTERRA
                    ENERGY TRUST

                
	 	 	
                  by
                    its Administrator

                
	 	 	
                  ENTERRA
                    ENERGY CORP.

                
	 	 	 
	 	 	 
	 	 	
                  Per:
                    /s/ Reg J. Greenslade

                
	 	 	
                  Reg
                    J. Greenslade, President and CEO

                
	 	 	 
	 	 	 
	 	 	 
	 	 	
                  ROCKY
                    MOUNTAIN GAS, INC.

                
	
                  ATTEST:

                	 	 
	 	 	 
	 	 	 
	
                  By:
                    /s/ Daniel P. Svilar

                	 	
                  By:
                    /s/ Mark J. Larsen

                
	
                  Daniel
                    P. Svilar, Secretary

                	 	
                  Mark
                    J. Larsen, President

                
	 	 	 
	 	 	 
	 	 	 
	 	 	
                  U.S.
                    ENERGY CORP.

                
	
                  ATTEST:

                	 	 
	 	 	 
	 	 	 
	
                  By:
                    /s/ Daniel P. Svilar

                	 	
                  By:
                    /s/ Keith G. Larsen

                
	
                  Daniel
                    P. Svilar, Secretary

                	 	
                  Keith
                    G. Larsen, President

                
	 	 	 
	 	 	 
	 	 	 
	 	 	
                  CRESTED
                    CORP. 

                
	
                  ATTEST:

                	 	 
	 	 	 
	 	 	 
	
                  By:
                    /s/ Daniel P. Svilar

                	 	
                  By:
                    /s/ Harold F. Herron

                
	
                  Daniel
                    P. Svilar, Secretary

                	 	
                  Harold
                    F. Herron, President

                


        

      

    

     

     

     

    
      
         

      

      
        3