MODIFICATION AGREEMENT

Exhibit 10.3

                                       $10,000,000.00 Multiple Advance Term Note

                                                            dated March 14, 2005

                             MODIFICATION AGREEMENT

This Modification Agreement ("Modification Agreement") is effective as of May 1,

2005. The parties to the Modification  Agreement are Natural Gas Services Group,

Inc. ("Borrower") and Western National Bank ("Lender").

                                    RECITALS

On March 14,  2005,  Borrower  executed  and  delivered  to Lender that  certain

Multiple  Advance  Term  Promissory  Note  in  the  original  principal  sum  of

$10,000,000.00, bearing interest at the rate stated therein, with a stated final

maturity  date of April 1, 2011 (the  "Note"),  pursuant to that certain  Fourth

Amended and Restated Loan Agreement dated March 14, 2005 (the "Loan Agreement").

All liens, security interests and assignments securing the Note are collectively

called the  "Liens".  Terms  defined in the Note or the Loan  Agreement  and not

otherwise  defined  herein  shall  have  the  same  meanings  here  as in  those

documents.

At  Borrower's  request,  Borrower  and  Lender  have  agreed to enter into this

Modification  Agreement  to modify the  interest  provisions  of the Note and to

ratify the Liens. Said modified interest provisions shall be effective as of May

1, 2005.

                                    AGREEMENT

1.  Modification  of Interest  Provisions  of the Note. In lieu of the following

provisions which were contained in the first paragraph of the Note:

                  "...at a rate per annum  which  shall from day to day be equal

         to the lesser of (a) a rate per annum (the "Established Rate") equal to

         the greater of (i) one percent  (1%) over the Prime Rate in effect from

         day to day, or (ii) six and  one-quarter  percent  (6.25%),  or (b) the

         Highest  Lawful Rate,  in each case  calculated  on the basis of actual

         days elapsed,  but computed as if each  calendar year  consisted of 360

         days."

such provisions of the Note are changed to read in their entirety as follows:

                  "...at a rate per annum  which  shall from day to day be equal

         to the lesser of (a) a rate per annum (the "Established Rate") equal to

         the  greater  of (i)  one-half  percent  (0.5%)  over the Prime Rate