Exhibit 10.3

                                       $10,000,000.00 Multiple Advance Term Note
                                                            dated March 14, 2005


                          SECOND MODIFICATION AGREEMENT
                          -----------------------------

This  Second  Modification   Agreement  ("Second  Modification   Agreement")  is
effective as of March 24, 2006. The parties to the Second 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, as modified in Modification  Agreement dated May
1, 2005 (the "Note").  The Note was made pursuant to that certain Fourth Amended
and Restated  Loan  Agreement  dated March 14, 2005, as modified in that certain
First  Modification  to Fourth Amended and Restated Loan Agreement  dated May 1,
2005;  and  further  amended  and  restated in that  certain  Fifth  Amended and
Restated  Loan  Agreement  dated  September  26, 2005;  and further  amended and
restated in that certain Sixth amended and Restated Loan Agreement dated January
3, 2006 (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 Second
Modification  Agreement  to modify the  interest  provisions  of the Note and to
ratify the Liens. Said modified interest provisions shall be effective as of the
April 1, 2006 payment.

                                    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-half  percent  (0.5%) 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:




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         "...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
         Prime Rate in effect from day to day, 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."

2.  Ratification  of Liens.  Borrower  and Lender  further  agree that all Liens
securing  the Note  shall  continue  and  carry  forward  until the Note and all
indebtedness  evidenced  thereby is paid in full.  Borrower  further agrees that
such liens are hereby ratified and affirmed as valid and subsisting  against the
collateral described therein, and that this Second Modification  Agreement shall
in no  manner  vitiate,  affect  or  impair  the Note or the  Liens  (except  as
expressly  modified in this Second  Modification  Agreement) and that such Liens
shall not in any manner be waived, released, altered or modified.

3. Miscellaneous.

         (a)      As modified  hereby,  the provisions of the Note and the Liens
                  shall  continue  in  full  force  and  effect,   and  Borrower
                  acknowledges  and affirms its liability to Lender  thereunder.
                  In  the  event  of  an   inconsistency   between  this  Second
                  Modification  Agreement  and the  terms  of the Note or of the
                  Liens, this Second Modification Agreement shall govern.

         (b)      Borrower hereby agrees to pay all costs and expenses  incurred
                  by Lender in connection with the execution and  administration
                  of this Second Modification Agreement.

         (c)      Any default by Borrower in the  performance of its obligations
                  herein contained shall constitute a default under the Note and
                  the Liens and shall allow Lender to exercise any or all of its
                  remedies  set  forth in such  Note  and  Liens or at law or in
                  equity.

         (d)      Lender does not, by its execution of this Second  Modification
                  Agreement, waive any rights it may have against any person not
                  a party hereto.

         (e)      All terms, provisions,  covenants,  agreements, and conditions
                  of the Note and the Liens are  unchanged,  except as  provided
                  herein.   Borrower   agrees  that  this  Second   Modification
                  Agreement and all of the covenants  and  agreements  contained
                  herein shall be binding  upon  Borrower and shall inure to the
                  benefit  of  Lender  and  each  of  their  respective   heirs,
                  executors,  legal representatives,  successors,  and permitted
                  assigns.

                  THIS  SECOND  MODIFICATION   AGREEMENT  REPRESENTS  THE  FINAL
                  AGREEMENT  BETWEEN THE PARTIES AND MAY NOT BE  CONTRADICTED BY
                  EVIDENCE  OF  PRIOR,   CONTEMPORANEOUS,   OR  SUBSEQUENT  ORAL
                  AGREEMENTS  OF  THE  PARTIES.  THERE  ARE  NO  UNWRITTEN  ORAL
                  AGREEMENTS BETWEEN THE PARTIES.



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                                    Borrower:
                                    ---------

                                    Natural Gas Services Group, Inc.


                                    By: /s/ Stephen C. Taylor
                                       -----------------------------------------
                                       Stephen C. Taylor, President


                                    Lender:
                                    -------

                                    Western National Bank


                                    By:      /s/ Scott A. Lovett
                                       -----------------------------------------
                                       Scott A. Lovett, Executive Vice President


STATE OF TEXAS             ss.
                           ss.
COUNTY OF MIDLAND          ss.

         This  instrument  was  acknowledged  before  me on March 31,  2006,  by
Stephen C. Taylor,  President of Natural Gas  Services  Group,  Inc., a Colorado
corporation, on behalf of said corporation.



                                       -----------------------------------------
                                       Notary Public, State of Texas


STATE OF TEXAS             ss.
                           ss.
COUNTY OF MIDLAND          ss.

         This instrument was acknowledged  before me on March 31, 2006, by Scott
A. Lovett, Executive Vice President of Western National Bank, a national banking
association, on behalf of said association.



                                       -----------------------------------------
                                       Notary Public, State of Texas







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