Exhibit 10.2
MULTIPLE ADVANCE TERM PROMISSORY NOTE

      $16,891,105.87   October 15, 2006

     FOR VALUE RECEIVED, in the manner, on the dates and in the amounts herein
stipulated, NATURAL GAS SERVICES GROUP, INC., a Colorado corporation (the
“Borrower”), hereby promises and agrees to pay to the order of WESTERN NATIONAL
BANK, a national banking association (the “Lender”), in Midland, Midland County,
Texas, the principal sum of SIXTEEN MILLION EIGHT HUNDRED NINETY-ONE THOUSAND
ONE HUNDRED FIVE AND 87/100 DOLLARS ($16,891,105.87) (the “Total Principal
Amount”), or such amount less than the Total Principal Amount which is
outstanding from time to time if the total amount outstanding under this
Promissory Note (this “Note”) is less than the Total Principal Amount, together
with interest at the rate of Seven and one-half percent (7.50%) per annum on
such portion of the Total Principal Amount which has been advanced to Borrower
from the date advanced until paid as hereinafter provided. Interest on the
indebtedness evidenced by this Note shall be calculated on the basis of a three
hundred sixty (360) day year.
     This Note is given in renewal, extension and modification, but not in
extinguishment, of that certain $10,000,000.00 Multiple Advance Term Promissory
Note dated March 14, 2005, as modified effective March 24, 2006, and further
modified effective August 28, 2006, and is the $10,000,000.00 Multiple Advance
Term Promissory Note referred to in the Fourth Amended and Restated dated March
14, 2005, by and between the Borrower, the Guarantor, and the Lender (the “Prior
Loan Agreement”). This Note is made pursuant to that certain Seventh Amended and
Restated Loan Agreement, as the same may be amended, supplemented or otherwise
modified from time to time, the “Loan Agreement”), by and among Borrower, the
Guarantor, and the Lender, and is subject to the terms and conditions thereof.
Reference is made to the Loan Agreement for provisions for the disbursement of
funds hereunder and for a further statement of the rights, remedies, powers,
privileges, benefits, duties and obligations of Borrower, Guarantor and Lender
under the Loan Agreement and this Note. Terms used herein which are defined in
the Loan Agreement shall have such defined meanings unless otherwise defined
herein. The holder of this Note shall be entitled to the benefits of the Loan
Agreement.
     Subject to the terms hereof and of the Loan Agreement, from the date of
this Note until maturity, the Lender will make Advances and Subsequent Advances
under this Note in accordance with the provisions of the Loan Agreement. The
aggregate principal amount of all such Advances as may be made by the Lender to
the Borrower under this Note shall never exceed Sixteen Million Eight Hundred
Ninety-One Thousand One Hundred Five and 87/100 Dollars ($16,891,105.87).
     The principal of this Note shall be due and payable in (a) fifty-nine
(59) consecutive monthly installments which shall each be in an amount of
$281,500.00, with the first such installment being due and payable on
November 1, 2006, and a like installment being due and payable on the first
(1st) day of each succeeding month, to and including September 1, 2011, and

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(b) one final installment in an amount equal to all remaining unpaid principal
and accrued and unpaid interest on this Note shall be due and payable on
October 1, 2011. Interest computed on the unpaid balance of this Note, shall be
due and payable monthly as it accrues, on the same dates as, but in addition to,
each installment of principal. All payments and prepayments shall be applied
first to accrued and unpaid interest, and the balance to principal. Partial
prepayments of principal shall be applied to the installments of principal
thereof in the inverse order of their maturity. All of the past due principal
and accrued interest hereunder shall, at the option of Lender, bear interest
from maturity (stated or by acceleration) until paid at a rate per annum equal
to the Highest Lawful Rate. The interest rate on this Note is a fixed rate until
maturity. Any adjustment downward as a result or otherwise is subject to an
adjustment fee.
     This Note is secured as provided in the Loan Agreement and in the other
Loan Papers, to which reference is hereby made for a description of the
properties and assets in which a lien and security interest has been granted,
the nature and extent of the security, the terms and conditions upon which the
liens and security interests were granted and the rights of the holder of this
Note with respect thereto.
     Time is of the essence of this Note. Upon the occurrence of any one or more
of the Events of Default specified in the Loan Agreement (after expiration of
any applicable notice and cure periods), all amounts then remaining unpaid on
(a) this Note and (b) the Revolving Line of Credit Promissory Note dated
October 15, 2006, from Borrower to Lender in the original principal amount of
$40,000,000.00, shall become, or may be declared to be, immediately due and
payable, all as provided therein.
     Upon the occurrence and during the continuance of any Event of Default, or
if Borrower or Guarantor become insolvent, however evidenced, Lender is hereby
authorized at any time and from time to time, without prior notice to Borrower
or Guarantor, to setoff and apply any and all deposits (general or special, time
or demand, provisional or final) at any time held or other indebtedness at any
time owing by Lender to or for the credit or the account of Borrower or
Guarantor against any and all of the Obligations, irrespective of whether or not
Lender shall have made any demand under the Loan Agreement or this Note and
although such Obligations may be unmatured. Lender agrees promptly to notify
Borrower or Guarantor after any such setoff and application, provided that the
failure to give such notice shall not affect the validity of such setoff and
application. The rights of Lender under this paragraph are in addition to other
rights and remedies (including, without limitation, other rights of setoff)
which Lender may have.
     Borrower and any and all co-makers, endorsers, guarantors and sureties
severally waive notice (including, but not limited to, notice of protest, notice
of dishonor, notice of intent to accelerate and notice of acceleration), demand,
presentment for payment, protest, diligence in collecting or bringing suit and
the filing of suit for the purpose of fixing liability, and consent that the
time of payment hereof may be extended and re-extended from time to time without
notice to them or any of them, and each agrees that his, her or its liability on
or with respect to this Note shall not be affected, diminished or impaired by
any (a) release of any security at any time existing for this Note,
(b) substitution for any security at any time existing for this Note, or
(c) failure to perfect

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(or to maintain perfection of) any lien on or security interest in any such
security, in each case in whole or in part, with or without notice, before or
after maturity.
     It is the intention of Borrower and Lender that Lender shall conform
strictly to usury laws applicable to it. Accordingly, if the transactions
contemplated by the Loan Agreement and this Note would be usurious as to Lender
under laws applicable to it (including the laws of the United States of America
and the State of Texas or any other jurisdiction whose laws may be mandatorily
applicable to Lender notwithstanding the other provisions of the Loan Agreement
and this Note), then, in that event, notwithstanding anything to the contrary in
this Note, the Loan Agreement or any other Loan Paper or other agreement entered
into in connection with or as security for this Note, (i) the aggregate of all
consideration which is contracted for, taken, reserved, charged or received by
Lender under this Note, the Loan Agreement or any other Loan Paper or agreement
entered into in connection with or as security for this Note shall under no
circumstances exceed the maximum amount allowed by such applicable law, and any
excess shall be credited by Lender on the principal amount of the Obligations to
Lender (or, to the extent that the principal amount of the Obligations shall
have been or would thereby be paid in full, refunded by Lender to the Borrower);
and (ii) in the event that the maturity of this Note is accelerated by reason of
an Event of Default under the Loan Agreement or otherwise, or in the event of
any prepayment, then such consideration that constitutes interest under law
applicable to Lender may never include more than the maximum amount allowed by
such applicable law, and excess interest, if any, provided for in this Note, the
Loan Agreement or otherwise shall be cancelled automatically by Lender as of the
date of such acceleration or prepayment and, if theretofore paid, shall be
credited by Lender on the principal amount of the Obligations (or, to the extent
that the principal amount of such Obligations shall have been or would thereby
be paid in full, refunded by Lender to the Borrower).
     To the extent that Texas Finance Code Section 303.002 is relevant to Lender
for the purposes of determining the Highest Lawful Rate, the applicable rate
ceiling under such provisions shall be determined by the indicated (weekly) rate
ceiling from time to time in effect, subject to Lender’s right subsequently to
change such method in accordance with applicable law. Notwithstanding anything
to the contrary contained herein or in any of the other Loan Papers, it is not
the intention of the Lender to accelerate the maturity of any interest that has
not accrued at the time of such acceleration or to collect unearned interest at
the time of such acceleration.
     THIS NOTE HAS BEEN EXECUTED UNDER, AND SHALL BE CONSTRUED AND ENFORCED IN
ACCORDANCE WITH, THE LAWS OF THE STATE OF TEXAS, EXCEPT AS SUCH LAWS ARE
PREEMPTED BY APPLICABLE FEDERAL LAWS. THIS NOTE HAS BEEN ENTERED INTO IN MIDLAND
COUNTY, TEXAS, AND IT SHALL BE PERFORMABLE FOR ALL PURPOSES IN MIDLAND COUNTY,
TEXAS. COURTS WITHIN THE STATE OF TEXAS SHALL HAVE JURISDICTION OVER ANY AND ALL
DISPUTES BETWEEN BORROWER AND LENDER, WHETHER AT LAW OR IN EQUITY, AND VENUE IN
ANY SUCH

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DISPUTE, WHETHER IN FEDERAL OR STATE COURTS, SHALL BE LAID IN MIDLAND COUNTY,
TEXAS. BORROWER HEREBY CONSENTS TO PERSONAL JURISDICTION IN MIDLAND COUNTY,
TEXAS AND WAIVES ANY RIGHTS IT MAY HAVE TO BE SUED ELSEWHERE.
     BORROWER AND THE HOLDER OF THIS NOTE (BY ITS ACCEPTANCE HEREOF) HEREBY
VOLUNTARILY, KNOWINGLY, IRREVOCABLY AND UNCONDITIONALLY WAIVE ANY RIGHT TO HAVE
A JURY PARTICIPATE IN RESOLVING ANY DISPUTE (WHETHER BASED UPON CONTRACT, TORT
OR OTHERWISE) BETWEEN OR AMONG BORROWER AND SUCH HOLDER ARISING OUT OF OR IN ANY
WAY RELATED TO THIS NOTE, AND OTHER LOAN DOCUMENT OR ANY RELATIONSHIP BETWEEN
HOLDER AND BORROWER RELATED TO THE LOAN EVIDENCED BY THE LOAN DOCUMENTS. THIS
PROVISION IS A MATERIAL INDUCEMENT TO THE HOLDER OF THIS NOTE TO PROVIDE THE
FINANCING DESCRIBED HEREIN AND IN THE OTHER LOAN DOCUMENTS.
     THIS NOTE, THE LOAN AGREEMENT, AND THE OTHER LOAN PAPERS REPRESENT THE
ENTIRE AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF
PRIOR, CONTEMPORANEOUS, OR SUBSEQUENT ORAL AGREEMENTS BETWEEN THE PARTIES. THERE
ARE NO UNWRITTEN AGREEMENTS BETWEEN THE PARTIES.

            NATURAL GAS SERVICES GROUP, INC.
      By:        /s/ Stephen C. Taylor              Stephen C. Taylor,
President             

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