Exhibit
      10.56

     

    AMENDMENT
      NO. 1 TO COLOMBIAN PARTICIPATION AGREEMENT

     

    THIS
      AMENDMENT NO. 1 TO COLOMBIAN PARTICIPATION AGREEMENT (this “Amendment”)
      is
      entered into as of the 1st day of November, 2006, by and among Argosy
Energy
      International, a Utah limited partnership (“Argosy”),
      Gran
      Tierra Energy Inc., a Nevada corporation (“Gran
      Tierra”),
      and
      Crosby Capital, LLC, a Texas limited liability company (“Crosby”).
      The
      entities named above may also be referred to herein individually as a
“Party”
or
      collectively as the “Parties.”
All
      capitalized terms not otherwise defined herein shall be given the
      meanings assigned to such terms in that certain Colombian Participation
      Agreement, dated as of
      June
      22, 2006, by and among Argosy, Gran Tierra, and Crosby (the “Original
      Participation Agreement”)

     

    RECITALS

     

    WHEREAS,
      the Parties executed the Original Participation Agreement, a copy of which
      is attached hereto as Exhibit A, on June 22, 2006;

     

    WHEREAS,
      the Parties desire to amend the Original Participation Agreement as set forth
      herein; and

     

    WHEREAS,
      pursuant to Section 13.4 of the Original Participation Agreement, no
      modification or waiver of any provision of the Original Participation Agreement
      shall be effective unless set forth in writing signed by the
      Parties.

     

    AGREEMENT

     

    NOW,
      THEREFORE, in consideration of the covenants and agreements herein, and other
      good and valuable consideration, the receipt and sufficiency of which are hereby
      acknowledged, the Parties agree as follows:

     

    
      	
              1.

            	
              Section
                6.2.1(a) of the Original Participation Agreement is hereby amended
                and
                restated in its entirety to read as
                follows:

            


    

     

    “(a) Amount:
      The
      face amount of the Initial Letter of Credit shall be USD$4,000,000.00. Draws
      from the Initial Letter of Credit must be replaced, within 45 days of any such
      draws, to keep the required USD$4,000,000.00 face value of the Letter
      of Credit in place. In the event that Crosby properly draws on the Initial
      Letter of Credit, Gran Tierra shall, within 45 days of such draw, provide a
      new
      Letter of Credit, in substantially similar form, with substantially similar
      terms as the Initial Letter of Credit and with a face amount equal to the amount
      of such draw so that the undrawn face amount
      of
      all Letters of Credit issued to Crosby to secure Gran Tierra’s obligations under
      this Agreement shall, at all times after 45 days following any draw thereunder
      during the Initial Term, equal USD$4,000,000.00. If Gran Tierra fails to provide
      such new Letter of Credit within the applicable 45 day period, in breach of
      the
      foregoing, Crosby may draw the remaining undrawn amount of the Initial Letter
      of
      Credit and cause the proceeds of such
      draw
      to be deposited to the Crosby Escrow Account (as defined in Section 6.5) as
      set
      forth
      in Section 6.5.”

    

      Amendment
        No. 1 to

      Colombian
        Participation Agreement

    

     

    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    


    
      	
              2.

            	
              The
                definition of “Issuer
                Acceptable Credit Rating,”
                set forth in Section 6.2.1(c) of the Original Participation Agreement
                shall be amended, and Section 6.2.1(c) of the Original Participation
                Agreement is hereby amended and restated in its entirety to read
                as
                follows:

            


    

     

    “(c) Issuer.
      The
      Initial Letter of Credit on terms consisted with this Section 6 and Exhibit
      A
      attached hereto, with such other documentary conditions as may be acceptable
      to Crosby shall be issued by a bank with a minimum credit rating of any of
      the following: (i) BBB, by Standard and Poor’s, (ii) Baa2 by Moody’s Investor
      Services, or (iii) BBB by Fitch IBCA (the “Issuer
      Acceptable Credit Rating”).
      Crosby may request and Gran

     

    Tierra
      shall then promptly provide a replacement standby letter of credit in accordance
      with the terms of Section 6 if the Issuer Acceptable Credit Rating declines
      below BBB (if Standard and Poor’s or Fitch IBCA) or Baa2 (if Moody’s Investor
      Services).”

     

    
      	
              3.

            	
              Section
                II to Exhibit A of the Original Participation Agreement is hereby
                amended
                and restated in its entirety to read as
                follows:

            


    

     

    “II Letter
      of Credit Renewal Default.

     

    Crosby
      shall be entitled to draw on the Letter of Credit in full and
      deposit
      such amount in an escrow account at the Crosby Escrow Bank if and only if it
      certifies to the Issuer Bank with reasonable evidence attached thereto that
      the
      money will be deposited in
      such
      escrow and any of the following three conditions are satisfied:

     

    A. if
      Gran
      Tierra fails to extend the expiration date of the Initial Letter of Credit
      to
      ensure that the Initial Letter of Credit remains outstanding until the expiry
      of
      the Initial Term, pursuant to Section
      6.2;
      or

     

    B. both
      (i)
      not less than 60 days nor more than 90 days prior to the end of any Letter
      of
      Credit term, Crosby delivered written notice to Gran Tierra, Argosy and/or
      any
      permitted transferee, that any of them, as the case may be, is required under
      Section
      6 and
      this
Exhibit
      A
      to
      deliver to Crosby a Letter of Credit satisfying the terms set forth in
Section
      6
      and this
Exhibit
      A,
      and
      (ii) Gran Tierra, Argosy or such permitted transferee has
      not
      within ten (10) business days provided such new Letter of Credit;
      or

     

    C. after
      45
      days following any draw under a Letter of Credit, Gran Tierra, Argosy or any
      permitted transferee has not provided a new Letter of Credit required
under
      Section 6.2.1(a) such that the undrawn face amount of all Letters of Credit
      issued to
      Crosby
      to secure Gran Tierra’s obligations under this Agreement is not, at all times
after
      45
      days following any draw during the Initial Term, equal to
      USD$4,000,000.00.”

     

    
      	
              4.

            	
              Article
                9 of the Original Participation Agreement is hereby amended by adding
                Section 9.3 to Article 9, as
                follows:

            


    

    

      Amendment
        No. 1 to

      Colombian
        Participation Agreement

    

     

    
      
        
        

      

      
        -
          2 -

        
          

        

      

      
        
        

      

    


    “9.3 Letter
      of Credit Rights Upon Assignment.
      If
      Crosby and/or any of the Crosby Members sells, assigns, transfers or otherwise
      disposes of any or all of the Participation Rights pursuant to Section 9.1
      or
      Section 9.2, and any Person other than Crosby is designated as the sole
      representative of the assignees of the Participation Rights pursuant to Section
      9.1.1, then Crosby shall have the right, upon written request to Gran Tierra
      which identifies such designated representative, to obtain the issuance of
      a
      replacement Letter of Credit (the “Replacement Letter of Credit”) on
      substantially the same
      terms as the Letters of Credit issued pursuant to Article 6, but naming the
      designated representative as beneficiary. The Replacement Letter of Credit
      shall only be issued by the issuing bank upon Crosby’s tender, to the issuing
      bank, of all Letters of Credit naming Crosby as beneficiary. Gran Tierra, Crosby
      and Argosy shall take such actions as are reasonably necessary to cause the
      issuing bank to issue the Replacement Letter of Credit to the designated
      representative as soon as practical following such written
      request. If the request to issue a Replacement Letter of Credit is received
      by
      Gran Tierra within 30 days of a date that Gran Tierra is obligated to procure
      a
      new or replacement Letter of Credit for any reason other than the obligations
      under this Section 9.3, the costs of obtaining the issuance of the Replacement
      Letter of Credit will be borne by Gran Tierra. If the request for the
      Replacement Letter of Credit is received by Gran Tierra at any time other than
      the foregoing, the out-of-pocket costs incurred by Gran Tierra
      for obtaining the issuance of the Replacement Letter of Credit shall be borne
      by
      Crosby. Gran Tierra shall not be deemed to have violated this Section 9.3 if
      it
      refuses to obtain the issuance of the Replacement Letter of Credit until the
      reimbursement of such costs is made or adequately provided for to the
      satisfaction of Gran Tierra.”

     

    
      	
              5.

            	
              The
                Initial Letter of Credit to be issued to Crosby pursuant to Section
                6 of
                the Original Purchase Agreement shall be in substantially the form
                attached hereto as Exhibit
                B.

            


    

     

    
      
        
          	6.	
                  References
                    to the “Agreement”
                    in the Original Participation Agreement shall be deemed to
                    include the Original Participation Agreement, as amended by this
                    Amendment. Except as expressly modified or otherwise as set forth
                    herein,
                    the terms and conditions of the Original Participation Agreement
                    remain in
                    full force and effect.

                


        

      

    

     

    [SIGNATURES
      ON NEXT PAGE]

    

      Amendment
        No. 1 to

      Colombian
        Participation Agreement

    

     

    
      
        
        

      

      
        -
          3 -

        
          

        

      

      
        
        

      

    


    IN
      WITNESS WHEREOF, the duly authorized representatives of the Parties have caused
      this Amendment to be executed on the date first written above.

     

    
      	
              ARGOSY
                ENERGY INTERNATIONAL

            
	 
	
              By:

            	
              /s/
                James Hart 

            
	
              Name: 

            	
              James
                Hart

            
	
              Title:

            	
              Secretary

            
	 
	
              GRAN
                TIERRA ENERGY INC.

            
	 
	
              By:

            	
              /s/
                James Hart

            
	
              Name: 

            	
              James
                Hart

            
	
              Title:

            	
              Chief
                Financial Officer

            
	 
	
              CROSBY
                CAPITAL, LLC

            
	 
	
              By:

            	
              /s/
                Jay Allen Chaffee

            
	
              Name: 

            	
              Jay
                Allen Chaffee

            
	
              Title:

            	
              President

            


    


    Amendment
      No. 1 to

    Colombian
      Participation Agreement

     

    
      
        
        

      

      
        -
          4 -

        
          

        

      

      
        
        

      

    

     

    Exhibit
      A

     

    [Original
      Participation Agreement attached hereto]


    Amendment
      No. 1 to

    Colombian
      Participation Agreement


    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    


    Original
      Participation Agreement Not Recopied

    

      Amendment
        No. 1 to

      Colombian
        Participation Agreement

    

    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    


    Exhibit
      B

     

    [Form
      of the Initial Letter of Credit attached hereto]

    

      Amendment
        No. 1 to

      Colombian
        Participation Agreement

    

     

    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    


    IRREVOCABLE
      STANDBY LETTER OF CREDIT

     

    Effective
      as of 31st October, 2006

     

    Irrevocable
      Letter of Credit No. [ ]

     

    
      	 	
              APPLICANT:

              GRAN
                TIERRA ENERGY INC.

              300,
                611 — 10th
                Avenue S.W.

              Calgary,
                Alberta

              Canada
                T2R OBZ

               

            
	 	
              STATED
                AMOUNT:

              USD
                $4,000,000

               

            
	 	
              EXPIRY
                DATE

              31st
                October, 2007

              (save
                as such date may be extended pursuant to paragraph 9 below)

              AT
                OUR COUNTERS

            


    

    


    BENEFICIARY:

    CROSBY
      CAPITAL, LLC

    712
      Main
      Street, Suite 1700

    Houston,
      TX 77002

    Attention:
      Jay Allen Chaffee

     

    Re: Colombian
      Participation Agreement 

    


    1. We,
      Standard Bank Plc (the “Issuing
      Bank”),
      hereby issue our irrevocable Standby Letter of Credit on behalf of Gran Tierra
      Energy Inc (the “Applicant”)
      for an
      amount of USD 4,000,000 (Four Million United States Dollars) in favour of Crosby
      Capital, LLC (the “Beneficiary”).

     

    2. This
      Standby Letter of Credit covers all monies and liabilities (whether actual
      or
      contingent) for up to the amount of USD 4,000,000 (Four Million United States
      Dollars) which are now or shall at any time hereafter be due, owing or payable
      to the Beneficiary from or by the Applicant under the terms of a participation
      agreement entered into on 22nd June, 2006 between the Applicant, Beneficiary
      and
      Argosy Energy International (as amended and in effect from time to time, the
      “Colombian
      Participation Agreement”).

     

    3. CLAIM
      DOCUMENTATION. Authenticated swift or tested telex claiming the sum due and
      in
      the appropriate form designated below:

     

    
      	
              (a)

            	
              if
                a claim is being made with respect to a payment default under the
                Colombian Participation Agreement, the form of Exhibit A
                hereto;

            


    

     

    
      	
              (b)

            	
              if
                a claim is being made with respect to a Letter of Credit renewal
                default
                under the Colombian Participation Agreement, the form of Exhibit
                B
                hereto;

            


    

     

    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    


    
      	
              (c)

            	
              if
                a claim is being made with respect to a default under the Columbian
                Participation Agreement in providing an additional Letter of Credit
                following a draw under a Letter of Credit, the form of Exhibit C;
                and/or

            


    

     

    
      	
              (d)

            	
              if
                a claim is being made with respect to an Issuing Bank credit rating
                downgrade under the Colombian Participation Agreement, the form of
                Exhibit
                D hereto.

            


    

     

    4. We
      hereby
      irrevocably and unconditionally undertake to honour all claims made by the
      Beneficiary in accordance with the terms and conditions of this Standby Letter
      of Credit within five (5) Business Days after our receipt thereof provided
      such
      claim documentation is received on or prior to 5:30pm (Greenwich Meantime)
      on
      the Expiry Date or on any day prior to the Expiry Date. For the purposes of
      this
      Standby Letter of Credit, “Business
      Day”
shall
      mean any day (other than a Saturday or Sunday) on which banks are open for
      business in London.

     

    5. It
      is
      further agreed that this Standby Letter of Credit shall be without prejudice
      to
      such rights as the Beneficiary may have at any time in respect of any security
      that the Beneficiary may hold for the said indebtedness and liabilities and
      that
      our liability shall not be affected by giving time or other indulgence to the
      Applicant, or by the Beneficiary realizing or entering into any compromise
      with
      depositors or any other collateral the Beneficiary may hold at any time in
      respect of the said liability.

     

    6. TT
      Reimbursement and partial drawings are allowed.

     

    7. This
      Standby Letter of Credit is not assignable.

     

    8. A
      person
      who is not a party to this Standby Letter of Credit has no right under the
      Contracts (Rights of Third Parties) Act 1999 to enforce the terms of this
      Standby Letter of Credit.

     

    9. Save
      as
      may be extended in accordance with the terms below, this Standby Letter of
      Credit expires at the counters of Standard Bank Plc on the Expiry Date. At
      any
      time no less than 90 days but no more than 120 days prior to the Expiry Date,
      the Applicant may by written notice addressed to the Issuing Bank request that
      the Expiry Date is extended for an additional period not to exceed one year.
      The
      Issuing Bank shall, no later than 30 days after receiving such request, notify
      the Beneficiary and the Applicant of its acceptance or rejection of such request
      and, if accepted, confirm the new Expiry Date.

     

    10. All
      documents presented to the Issuing Bank in connection with any demand for
      payment under this Letter of Credit, as well as all notices and other
      communications to the Issuing Bank in respect hereof, shall be in writing,
      shall
      make specific reference to this Standby Letter of Credit by number and shall
      be
      delivered to the Issuing Bank at its office located at Standard Bank PLC, Canon
      Bridge House, 25 Dowgate Hill, London, EC4R 2SB (or at any other office of
      the
      Issuing Bank as may be designated by the Issuing Bank by written notice
      delivered to the Beneficiary) by authenticated SWIFT message (or any other
      form
      of communication previously agreed in writing with the Issuing Bank) to the
      following address (or at any number(s) designated by the Issuing Bank by written
      notice delivered to the Beneficiary), as applicable: [please
      provide].

     

    11. This
      Standby Letter of Credit is subject to the Uniform Customs and Practice for
      Documentary Credits (1993 Revision), International Chamber of Commerce,
      Publication No. 500 (the “UCP”).
      This
      Standby Letter of Credit shall be governed by the laws of the State of New
      York,
      and the state and federal courts located in the State, County and City of New
      York shall have non-exclusive jurisdiction in any action or proceeding arising
      out of this Standby Letter of Credit.

     

    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    


    12. Demand
      for payment under this Standby Letter of Credit shall be presented directly
      to
      the Issuing Bank and shall not be negotiated.

     

    13. Standard
      Bank Plc’s charges are for the account of the Applicant, all other charges are
      for the account of the Beneficiary.

     

    14. By
      paying
      the Beneficiary an amount demanded in accordance with this Standby Letter of
      Credit, the Issuing Bank makes no representation as to the correctness of the
      amount demanded or of the calculations and representations of the Beneficiary
      required by this Letter of Credit.

     

    15. This
      Standby Letter of Credit sets forth in full the Issuing Bank’s undertaking, and
      such undertaking shall not be deemed in any way to be modified, amended,
      amplified or otherwise affected by any document, instrument or agreement
      referred to herein (including, without limitation, the Colombian Participation
      Agreement or credit agreement to which is relates), except only the Uniform
      Customs and the certificate(s)provided for herein.

     

    
      	STANDARD
              BANK PLC
	 	 
	
              By:

            	   
	
            
	
              Title:

            	  
	
            
	 	 
	
              By:

            	 
	
            
	
              Title:

            	  
	
            


    


    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    


    Exhibit
      A

    Irrevocable
      Letter of Credit

    No.
      ________

     

    CERTIFICATE
      FOR A PAYMENT DEFAULT

     

    The
      undersigned hereby certifies to Standard Bank PLC (the “Issuing
      Bank”),
      with
      reference to Irrevocable Letter of Credit No. _______ (the “Letter
      of Credit”)
      issued
      by the Issuing Bank in favor of Crosby Capital, LLC (the “Beneficiary”),
      and
      for the account of Gran Tierra Energy Inc. (the “Account
      Party”),
      that
      the undersigned is a duly authorized officer of the Beneficiary, that any
      capitalized term used but not defined herein shall have its respective meaning
      set forth in the Letter of Credit or the Colombian Participation Agreement
      referred to therein and that:

     

    The
      Beneficiary is entitled to draw $[  
      ] (the
“Draw
      Amount”)
      under
      the Letter of Credit, which is the exact amount that is owed to the Beneficiary
      under the Colombian Participation Agreement. The Beneficiary hereby directs
      the
      Issuing Bank to pay the Draw Amount by wire transfer of such amount in
      immediately available funds to the account of the Beneficiary specified
      below:

     

    Bank
      Name:

    Address:

    ABA
      No.:

    Account
      Name: 

    Account
      No.:

    Attention:

     

    [Include
      either [A] or [B].]

     

    [A]
      [The
      Beneficiary further certifies to the Issuing Bank that attached hereto is the
      written agreement of the Account Party acknowledging that the Draw Amount is
      due
      to the Beneficiary under the Colombian Participation Agreement and that the
      Account Party and its affiliates have failed to make such payment.]

     

    [B]
      [Include either [1] or [2]]

     

      
      [(1)] [The Beneficiary further certifies to the Issuing Bank that:

     

    (a) an
      award
      of the Panel provided in Section 11.2 of the Colombian Participation Agreement,
      provided for payment of the Draw Amount to the
      Beneficiary (the “Crosby
      Arbitration Award”);
      and

     

    (b) within
      10
      business days of the Crosby Arbitration Award, (i) the Crosby Arbitration Award
      has not been paid and (ii) the Crosby Arbitration
      Award has not been appealed.]

     

       [(2)]
      [The Beneficiary further certifies to the Issuing Bank that:

     

    (a) an
      award
      of the Panel provided in Section 11.2 of the Colombian Participation Agreement,
      provided for payment of the Draw Amount to the
      Beneficiary (the “Crosby
      Arbitration Award”);

     

    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    


    Exhibit
      A

    Irrevocable
      Letter of Credit

    No.
      ________

     

    (b) within
      10
      business days of the Crosby Arbitration Award, (i) the Crosby Arbitration Award
      was not paid and (ii) the Crosby Arbitration Award was appealed;

     

    (c) a
      final
      determination of the Crosby Arbitration Award favorable to

     

    the
      Beneficiary has been entered (the “Crosby
      Final Determination”)
      on
      appeal; and

     

    (d) the
      Beneficiary has not been paid in full the amount of the Crosby Final
      Determination within 5 business days of such Crosby Final
      Determination.]

    


    IN
      WITNESS WHEREOF, the Beneficiary has executed and delivered this Certificate
      as
      of the ____ day of __________, ____.

    


    
      	
              CROSBY
                CAPITAL, LLC

            
	 
	
              By:

            	 

	
              Title:

            	 



    

     

    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    


    Exhibit
      B

    Irrevocable
      Letter of Credit

    No.
      ________

     

    CERTIFICATE
      FOR A LETTER OF CREDIT RENEWAL DEFAULT

     

    The
      undersigned hereby certifies to Standard Bank PLC (the “Issuing
      Bank”),
      with
      reference to Irrevocable Letter of Credit No. _______ (the “Letter
      of Credit”)
      issued
      by the Issuing Bank in favor of Crosby Capital, LLC (the “Beneficiary”),
      and
      for the account of Gran Tierra Energy Inc. (the “Account
      Party”),
      that
      the undersigned is a duly authorized officer of the Beneficiary, that any
      capitalized term used but not defined herein shall have its respective meaning
      set forth in the Letter of Credit or the Colombian Participation Agreement
      referred to therein and that:

     

    The
      Beneficiary is entitled to draw the Letter of Credit in full and deposit the
      Stated Amount in the escrow account at the Crosby Escrow Bank specified below
      (the “Escrow
      Account”).
      The
      Crosby Escrow Agreement has been executed by each of the Beneficiary and the
      Crosby Escrow Bank, and contains the provisions required by the Colombian
      Participation Agreement. A copy of such executed Crosby Escrow Agreement is
      delivered herewith. The Beneficiary hereby directs the Issuing Bank to pay
      the
      Stated Amount under the Letter of Credit by wire transfer of such amount in
      immediately available funds directly to the Escrow Account, as
      follows:

     

    Bank
      Name:

    Address:

    ABA
      No.:

    Account
      Name: 

    Account
      No.:

    Attention:

     

    [Include
      either [A] or [B].]

     

    [A]
      The
      Beneficiary hereby further certifies to the Issuing Bank that: (I) the Initial
      Term has not expired; and (2) the Account Party has failed to extend the Expiry
      Date of the Letter of Credit for an additional one year, pursuant to Section
      9
      of the Letter of Credit.]

     

    [B]
      The
      Beneficiary hereby further certifies that:

     

    
      	 	
              (1)

            	
              not
                less than 60 days nor more than 90 days prior to the Stated Termination
                Date, the Beneficiary delivered written notice to the Account Party
                that
                the Account Party is required under Section 6 of the Participation
                Agreement to deliver to the Beneficiary confirmation of an extension
                of
                the Letter of Credit for an additional period equal to the shorter
                of (i)
                one year from the Stated Termination Date and (ii) the period ending
                on
                the last day of the Initial Term;
                and

            


    

     

    
      	 	
              (2)

            	
              the
                Account Party has not provided such an extension of the Letter of
                Credit
                prior to the date that is 10 Business Days following the date which
                is 60
                days prior to the Stated Termination
                Date.)

            


    

     

    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    


    Exhibit
      B

    Irrevocable
      Letter of Credit

    No.
      ________

     

    IN
      WITNESS WHEREOF, the Beneficiary has executed and delivered this Certificate
      as
      of the ____ day of __________, ____.

     

    
      	
              CROSBY
                CAPITAL, LLC

            
	 	 
	
              By:

            	 

	
              Title:
                

            	 



    

     

    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    


    Exhibit
      C

    Irrevocable
      Letter of Credit

    No.
      ________

     

    CERTIFICATE
      FOR A LETTER OF CREDIT REINSTATEMENT DEFAULT

     

    The
      undersigned hereby certifies to Standard Bank PLC (the “Issuing
      Bank”),
      with
      reference to Irrevocable Letter of Credit No. ______ (the “Letter
      of Credit”)
      issued
      by the Issuing Bank in favor of Crosby Capital, LLC (the “Beneficiary”),
      and
      for the account of Gran Tierra Energy Inc. (the “Account
      Party”),
      that
      the undersigned is a duly authorized officer of the Beneficiary, that any
      capitalized term used but not defined herein shall have its respective meaning
      set forth in the Letter of Credit or the Colombian Participation Agreement
      referred to therein and that:

     

    The
      Beneficiary is entitled to draw the remaining undrawn portion of the Stated
      Amount of the Letter of Credit (the “Remaining
      Amount”)
      and
      deposit the Remaining Amount in the escrow account at the Crosby Escrow Bank
      specified below (the “Escrow
      Account”).
      The
      Crosby Escrow Agreement has been executed by each of the Beneficiary and the
      Crosby Escrow Bank, and contains the provisions required by the Colombian
      Participation Agreement. A copy of such executed Crosby Escrow Agreement is
      delivered herewith. The Beneficiary hereby directs the Issuing Bank to pay
      the
      Remaining Amount under the Letter of Credit by wire transfer of such amount
      in
      immediately available funds directly to the Escrow Account, as
      follows:

     

    Bank
      Name:

    Address:

    ABA
      No.:

    Account
      Name: 

    Account
      No.:

    Attention:

     

    The
      Beneficiary hereby further certifies that, following a prior draw under a Letter
      of Credit, the Account Party has failed to deliver a new letter of Credit to
      the
      Beneficiary in the amount of such draw within 45 days of such draw as required
      by the Columbian Participation Agreement.

     

    IN
      WITNESS WHEREOF, the Beneficiary has executed and delivered this Certificate
      as
      of the ____ day of __________, ____.

     

    
      	
              CROSBY
                CAPITAL, LLC

            
	 
	
              By:

            	  
              
	
              Title:
                

            	  
              


    


    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    


    Exhibit
      D

    Irrevocable
      Letter of Credit

    No.
      ________

    


    CERTIFICATE
      FOR AN ISSUING BANK CREDIT

    RATING
      NON-MAINTENANCE DEFAULT

     

    The
      undersigned hereby certifies to Standard Bank PLC (the “Issuing
      Bank”),
      with
      reference to Irrevocable Letter of Credit No. ______ (the “Letter
      of Credit”)
      issued
      by the Issuing Bank in favor of Crosby Capital, LLC (the “Beneficiary”),
      and
      for the account of Gran Tierra Energy Inc. (the “Account
      Party”),
      that
      the undersigned is a duly authorized officer of the Beneficiary, that any
      capitalized term used but not defined herein shall have its respective meaning
      set forth in the Letter of Credit or the Colombian Participation Agreement
      referred to therein and that:

     

    The
      Beneficiary is entitled to draw the Letter of Credit in full and deposit the
      Stated Amount in the escrow account at the Crosby Escrow Bank specified below
      (the “Escrow
      Account”).
      The
      Crosby Escrow Agreement has been executed by each of the Beneficiary and the
      Crosby Escrow Bank, and contains the provisions required by the Colombian
      Participation Agreement. A copy of such executed Crosby Escrow Agreement is
      delivered herewith. The Beneficiary hereby directs the Issuing Bank to pay
      the
      Stated Amount under the Letter of Credit by wire transfer of such amount in
      immediately available funds directly to the Escrow Account, as
      follows:

     

    Bank
      Name:

    Address:

    ABA
      No.:

    Account
      Name: 

    Account
      No.:

    Attention:

     

    The
      Beneficiary hereby further certifies that:

     

    
      	 	
              A.

            	
              the
                Beneficiary delivered written notice to the Account Party that the
                Issuing
                Bank’s credit rating has fallen below the Issuer Acceptable Credit Rating
                and requested delivery of a replacement Letter of Credit as required
                under
                Section 6 of the Participation Agreement;
                and

            


    

     

    
      	 	
              B.

            	
              the
                Account Party has not within 15 business days following receipt of
                such
                notice provided such a replacement Letter of
                Credit.

            


    

     

    


    IN
      WITNESS WHEREOF, the Beneficiary has executed and delivered this Certificate
      as
      of the ____ day of __________, ____.

     

    


    
      	
              CROSBY
                CAPITAL, LLC

            
	 
	
              By:

            	  
              
	
              Title: