EXHIBIT 10.10

                                 PROMISSORY NOTE
                             MODIFICATION AGREEMENT

     This Promissory Note Modification Agreement (the "Agreement") is made
effective as of June 25, 2002 ("Effective Date") by and between Kenneth L. Agee
("Maker") and Syntroleum Corporation, a Delaware Corporation ("Lender").

     WHEREAS, on June 25, 2001, Lender made certain loans to Maker in the
original amount of $1,100,000 and Maker executed and delivered a Secured
Promissory Note dated June 25, 2001 to Lender (the "Promissory Note");

     WHEREAS, the original due date of the Promissory Note was June 25, 2002;
and

     WHEREAS, the Promissory Note was secured by a security interest and pledge
of shares of the Common Stock of the Lender owned by the Maker pursuant to the
terms of a Security and Stock Pledge Agreement dated June 25, 2001 between
Lender and Maker ("Pledge Agreement"); and

     WHEREAS, Lender has made an additional advances to Maker in the amount of
$341,096.33; and

     WHEREAS, Maker and Lender desire, through this Agreement, to extend the
Promissory Note and to amend certain terms and provisions of the Promissory Note
as set forth below.

     NOW THEREFORE, in consideration of the mutual agreements set forth herein
and other good and valuable consideration, Maker and Lender, for themselves,
their heirs, personal representatives, successors and assigns, hereby agree as
follows:

     1.   Revisions to Note. Maker and Lender agree that the Promissory Note is
          hereby modified in the following respects:

          a.   commencing on the Effective Date, the interest rate under the
               Promissory note is hereby modified to 3.75% per annum.

          b.   the due date of the Promissory Note is hereby modified such that
               the principal and accrued interest will be due and payable on
               June 25, 2003.

          c.   the principal amount of the Promissory Note is hereby modified to
               the sum of $1,460,000.

          d.   In order to reflect the foregoing changes, the first paragraph
               and

          e.   the second paragraph of the Promissory Note are hereby modified
               to read as follows:



     FOR VALUE RECEIVED, the undersigned, KENNETH L. AGEE ("Maker"), promises to
     pay SYNTROLEUM CORPORATION, a Delaware corporation ("Lender"), at Suite
     1100, 1350 South Boulder, Tulsa, Oklahoma 74119, or such other address as
     Lender may designate, in lawful money of the United States of America in
     same day funds, the lesser of (i) U.S. $1,460,000 or (ii) the then
     outstanding principal amount of each loan (the "Loan" or "Loans") made by
     the Lender from time to time to the Maker hereunder. Principal and accrued
     interest will be due and payable on June 25, 2003. Maker may prepay this
     Note, in part or in full, at any time without penalty as to interest or
     principal.

     Each Loan shall bear interest payable at maturity at a rate of 3.75 % per
annum for each day principal is outstanding under this Note. Interest shall be
computed on the basis of a year of 365 days (or 366 days in a leap year) and
paid for actual days elapsed (including the first day but excluding the last
day).

     2.   Revisions to the Pledge Agreement. The Pledge Agreement is hereby
          modified to reflect the foregoing changes to the Promissory Note and
          is otherwise ratified, affirmed and approved.

     3.   No further changes. Except as expressly amended by this Agreement, the
          Promissory Note and Pledge Agreement are in all respects ratified and
          confirmed and all the terms, provisions, conditions, covenants,
          warranties and agreements set forth and contained therein shall be and
          remain in full force and effect and the lien and priority of the
          Pledge Agreement is hereby ratified and confirmed to the full extent
          of the indebtedness evidenced by the Promissory Note, as herein
          modified.

     In Witness Whereof, the parties have duly executed and delivered this
Agreement as of the effective date.


                                               ---------------------------------
                                               Kenneth L. Agee

                                               Syntroleum Corporation

                                               By
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