**Exhibit 10(i)a****AMENDMENT OF CREDIT AGREEMENT**          THIS AMENDMENT OF CREDIT AGREEMENT (this “Amendment”), dated as of December 31, 2006, isby and between BASIC EARTH SCIENCE SYSTEMS, INC. (“BESSI”), and AMERICAN NATIONAL BANK, anational banking association (“ANB”), f/k/a THE BANK OF CHERRY CREEK, N.A. (“BOCC”).**RECITALS**          A. BESSI and BOCC entered into a letter agreement dated March 4, 2002, as previouslyamended (as so amended, the “Credit Agreement”), setting forth the terms upon which BOCCwould make advances to BESSI and by which such advances would be governed and repaid.Capitalized terms used herein but not defined herein shall have the same meanings as set forthin the Credit Agreement.          B. ANB is the successor in interest to the rights and obligations of BOCC under theCredit Agreement and all related documents.          C. BESSI and ANB desire that this Amendment be executed and delivered inorder to amend certain terms and provisions of the Credit Agreement.**AMENDMENT**          NOW, THEREFORE, in consideration of $10.00 and other good and valuable consideration, thereceipt and sufficiency of which are hereby acknowledged, the parties hereby agree as follows: 1. Credit Agreement. The Credit Agreement shall be, and hereby is,amended as follows as of the date hereof: a. The following shall be substituted for the section entitled “MaturityDate” on page 2 of the Credit Agreement:   Maturity Date: December 31, 2008, on which date the Borrower agrees torepay the remaining balance of the Loan in its entirety,including all outstanding principal interest, fees, expenses,and other amounts due in connection therewith. b. The following shall be substituted for the section entitled “RevolvingPeriod” on page 2 of the Credit Agreement:   Revolving Period: From the date of this agreement through December 31,2008. During the Revolving Period Borrower may borrow, repay,and re-borrow funds. At no time, however, may the aggregateoutstanding principal balance of all Advances exceed theCommitment Amount.     Amendment of Credit Agreement Page 1 of  3 December 31, 2006
 

 
 c. As of December 31, 2006, the Borrowing Base shall be $4,000,000.  d. In the section entitled “Reporting Requirements” on page 5 of the CreditAgreement, item (e) shall be deleted in its entirety.  e. In the section entitled “Financial Covenants” on page 6 of the CreditAgreement, item (a) shall be replaced in its entirety with the following language:Borrower will maintain a debt-to-equity ratio less than 1.00, where thedebt-to-equity ratio is defined as debt (inclusive of all long term debt as definedunder GAAP plus any short term debt outstanding under this facility) divided byequity (as defined under GAAP). f. In the section entitled “Negative Covenants” on page 7 of the Credit Agreement,item (e) shall be replaced in its entirety with the following language:(e) sell, lease, or dispose of any assets during any 12-month period which have anaggregate value in excess of $100,000, 2. Loan Documents. All references in any document to the Credit Agreement shall bedeemed to refer to the Credit Agreement, as amended pursuant to this Amendment.  3. Conditions Precedent. The obligations of the parties under this Amendment aresubject, at the option of ANB, to the prior satisfaction of the condition that BESSI shall havedelivered to ANB the following (all documents to be satisfactory in form and substance toANB and, if appropriate, duly executed and/or acknowledged on behalf of the partiesother than ANB):a. This Amendment. 4. Certification by BESSI. BESSI hereby certifies to ANB that as of the date ofthis Amendment: (a) all of BESSI’s representations and warranties contained in the CreditAgreement are true, accurate and complete in all material respects, (b) BESSI hasperformed and complied with all agreements and conditions required to be performed orcomplied with by it under the Credit Agreement and/or any Loan Document on or prior to thisdate, and (c) neither any Event of Default nor any other event or condition which, with thegiving of notice, the lapse of time, or both, would constitute an Event of Default hasoccurred under the Credit Agreement.     Amendment of Credit Agreement Page 2 of  3 December 31, 2006
 

 
 5. Continuation of the Credit Agreement. Except as specified in this Amendment,the provisions of the Credit Agreement shall remain in full force and effect, and if there is aconflict between the terms of this Amendment and those of the Credit Agreement orany other document executed and delivered in connection therewith, the terms of thisAmendment shall control.  6. Miscellaneous. This Amendment shall be governed by and construed under the lawsof the State of Colorado and shall be binding upon and inure to the benefit of the parties heretoand their successors and assigns. This Amendment may be executed in any number ofcounterparts, each of which shall be an original, but all of which together shall constituteone instrument.     EXECUTED as of December 31, 2006.     BASIC EARTH SCIENCE SYSTEMS, INC.          By: /s/ Ray Singleton         Ray Singleton    President            By: /s/ David Flake         David Flake    Chief Financial Officer       AMERICAN NATIONAL BANK f/k/a  THE BANK OF CHERRY CREEK, N.A.          By: /s/ Gary W. Vick         Gary W. Vick    Vice President       Amendment of Credit Agreement Page 3 of  3 December 31, 2006