Document:

Exhibit 10.1

                              FIRST MODIFICATION TO
                           SECOND AMENDED AND RESTATED
                                 LOAN AGREEMENT

         This First  Modification  to Second Amended and Restated Loan Agreement
(the "First Modification") is made and entered into effective December 15, 2004,
by and among Natural Gas Services Group, Inc.  ("Borrower") and Western National
Bank ("Lender").

                                    RECITALS
                                    --------

         WHEREAS,  Borrower,  the guarantor parties thereto,  and Lender entered
into that certain Second  Amended and Restated Loan Agreement  dated November 3,
2003 (the "Loan Agreement"); and

         WHEREAS,  pursuant  to  the  Loan  Agreement,   Borrower  executed  and
delivered to Lender that certain  Advancing Line of Credit Promissory Note dated
November  3, 2003,  in the  original  principal  amount of  $10,000,000.00  (the
"Note"),  with an initial borrowing base of  $7,000,000.00,  and other terms and
conditions as set out in the Loan Agreement; and

         WHEREAS,  the  guarantor  parties  to the Loan  Agreement,  Rotary  Gas
Systems, Inc., NGE Leasing, Inc., and Great Lakes Compression,  Inc., which were
Subsidiaries of Borrower, have now merged into Borrower; and

         WHEREAS,  Borrower  and Lender now desire to modify the Loan  Agreement
(a) to increase in the borrowing  base of the Note, (b) to extend the period for
Borrower to request advances under the Note, and to modify certain other related
provisions of the Loan Agreement.

         NOW  THEREFORE,  in view of the foregoing and in  consideration  of the
mutual  covenants  and  agreements  hereinafter  contained,  Borrower and Lender
hereby agree as follows:

                                    ARTICLE 1
                         Modification of Loan Agreement
                         ------------------------------

         The Loan  Agreement  is hereby  amended on the  effective  date of this
amendment in the following respects:

1.       Paragraph 1.1 Defined Terms is amended in the following respects:

         "Advance  Note"  means the  Advancing  Line of Credit  Promissory  Note
         described in Section 2.1(b) hereof,  as modified on even date herewith,
         and  as the  same  may  be  further  renewed,  extended,  increased  or
         otherwise modified from time to time.

<PAGE>

2.       Paragraph  2.1(b)  Advance Type Term Loans is amended in the  following
         respects:

         "(b) Advance Type Term Loans.  Contemporaneously with the execution and
         delivery  hereof,  the Borrower shall execute and deliver to the Lender
         the Modification  Agreement in the form of Exhibit B hereto. Subject to
         and upon the terms and  conditions  of this  Agreement  and the Advance
         Note,  the  Borrower  may, at any time and from time to time during the
         period  commencing  on the date of the  Advance  Note and ending at the
         close of business on December  14, 2005,  request one or more  Advances
         and borrow  (without  the  ability to reborrow  amounts  paid under the
         Advance  Note)  under  the  Advance  Note;   provided,   however,   and
         notwithstanding  the face amount of the Advance Note, without the prior
         written  consent  of  Lender  in its  sole  discretion  the  cumulative
         aggregate principal amount of all Advances under the Advance Note shall
         never  exceed  the  lesser  of (i)  $10,000,000.00  or (ii) the  amount
         available  for Advance  under the Advance  Note and  Revolving  Line of
         Credit  Promissory  Note as determined in accordance with and set forth
         in line O in the Borrowing  Base Report.  The Advance Note shall mature
         as  provided  therein and shall bear  interest on the unpaid  principal
         amount thereof from time to time outstanding at the applicable interest
         rate per annum as provided in the Advance Note.  Principal and interest
         on the  Advance  Note  shall be  payable in the manner and on the dates
         specified  therein.  The Advance Note,  including  the loans  evidenced
         thereby,  is a multiple  advance  term loan  facility  and shall not be
         construed  as a  revolving  line  of  credit  as  reborrowings  are not
         permitted."

3.       Paragraph 3.2 Conditions to Subsequent Advances,  subparagraphs (d) and
         (e) are amended in the following respects:

         "(d)  After  giving  effect  to the  Advances  under the  Advance  Note
         requested by Borrower to be made on any date, the cumulative  aggregate
         principal  amount of all  Advances  under the  Advance  Note  shall not
         exceed $10,000,000.00.

         "(e) Each request for an Advance under the Advance Note shall have been
         received by Lender prior to December 14, 2005."

4.       Exhibit  D  Borrowing  Base  Report,  Line  P,  is  amended  to  delete
         $7,000,000.00 and substitute therefor $10,000,000.00.

                                    ARTICLE 2
                                  Miscellaneous
                                  -------------

1. The provisions of this First Modification to Second Amended and Restated Loan
Agreement  shall be binding  upon and shall  inure to the benefit of the parties
hereto and are  incorporated  by reference into the Loan Agreement as if set out
verbatim therein.

                                       2
<PAGE>

2. The Loan  Agreement,  as amended  herein,  is hereby  ratified,  adopted  and
confirmed by Borrower.  Each  agreement,  representation,  warranty and covenant
made by  Borrower  in the  Loan  Agreement  is  hereby  ratified,  adopted,  and
confirmed by Borrower on the date of execution hereof.

3. The effective date of this First  Modification to Second Amended and Restated
Loan Agreement  shall be December 15, 2004, at which time the provisions of this
First  Modification  to Second Amended and Restated Loan Agreement  shall become
operative and are incorporated into the Loan Agreement.

THIS WRITTEN  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.

         Executed on _____________, 2004, but effective as of December 15, 2004.

                                    BORROWER:

                                    Natural Gas Services Group, Inc.

                                    By:_________________________________________
                                       Wallace C. Sparkman, President

                                    LENDER:

                                    Western National Bank

                                    By:_________________________________________
                                       Scott A. Lovett, Executive Vice President

                                       3Exhibit 10.2

                             MODIFICATION AGREEMENT
                             ----------------------

This  Modification  Agreement  ("Modification  Agreement")  is  effective  as of
December 15, 2004.  The parties to the  Modification  Agreement  are Natural Gas
Services Group, Inc. ("Borrower") and Western National Bank ("Lender").

                                    RECITALS

On November 3, 2003,  Borrower  executed  and  delivered  to Lender that certain
Advancing  Line of  Credit  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 November 15, 2009 (the "Note"), pursuant to that certain Second
Amended  and  Restated  Loan  Agreement  dated  November  3,  2003  (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.

Contemporaneously  with the execution and delivery by Borrower to Lender of that
certain First Modification to Second Amended and Restated Loan Agreement of even
date herewith between Borrower and Lender, (the "First Modification"),  Borrower
and  Lender  agreed  (a) to  increase  the  Borrowing  Base  of said  Note  from
$7,000,00.00  to  $10,000,000.00,  (b) extend the period for Borrower to request
advances  under the Note from November 3, 2004, to December 14, 2005, (c) modify
the provisions  relating to the amortization of advances between the date hereof
and an December  14,  2005,  and (d) to make other  related  changes to the Loan
Agreement to incorporate such agreement and substitution.

Further, Borrower and Lender agreed to enter into this Modification Agreement to
modify the  interest  provisions  of the Note to provide  for an increase in the
interest floor from five and one-fourth percent (5.25%) to six percent (6%), and
to ratify the Liens.

AGREEMENT

1.  Modification  of Interest  Provisions  of the Note. In lieu of the following
provisions which were contained in the first paragraph of 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) five and  one-fourth  percent  (5.25%),  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."

<PAGE>

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 percent  (1%) over the Prime Rate in effect from
         day to day, or (ii) six percent (6.0%), 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.  Modification  of Payment  Provisions  of the Note.  In lieu of the following
provision which was contained in the fourth (4th) paragraph of the Note:

                  "The  principal  of this Note shall be due and  payable in (a)
         fifty-nine  consecutive monthly  installments which shall each be in an
         amount  equal to 1/60th of the  outstanding  principal  balance of this
         Note on December 15, 2004,  with the first such  installment  being due
         and payable on December 15, 2004, and a like installment  being due and
         payable on the fifteenth day of each succeeding  month to and including
         October 15, 2009;  and (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 November 15, 2009. 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."

such provision of the Note is changed to read as follows:

                  "The  principal  of this  Note  shall  be due and  payable  as
         follows:

         (a)      with respect to the principal  balance  outstanding under this
                  Note on December  15, 2004,  in  fifty-nine  (59)  consecutive
                  monthly installments of $116,666.67, with the first (1st) such
                  installment  being due and  payable on  December 5, 2004 and a
                  like installment being due and payable on the 15th day of each
                  succeeding month to and including October 15, 2009; plus

         (b)      1/60th of the sum of all  advances  made by Lender  under this
                  note after December 15, 2004 and prior to March 31, 2005 and a
                  like installment being due and payable on the 15th day of each
                  succeeding month to and including October 15, 2009; plus

         (c)      1/60th of the sum of all  advances  made by Lender  under this
                  note  after  April 1, 2005 and prior to June 30,  2005,  and a
                  like installment being due and payable on the 15th day of each
                  succeeding month to and including October 15, 2009; plus

         (d)      1/60th of the sum of all  advances  made by Lender  under this
                  note after July 1, 2005 and prior to September  30, 2005 and a
                  like installment being due and payable on the 15th day of each
                  succeeding month to and including October 15, 2009; plus

<PAGE>

         (e)      1/60th of the sum of all  advances  made by Lender  under this
                  note after  October 1, 2005 and prior to December 15, 2005 and
                  a like  installment  being due and  payable on the 15th day of
                  each succeeding month to and including October 15, 2009; plus

         (f)      one  final  installment  in an amount  equal to all  remaining
                  unpaid  principal and accrued and unpaid  interest on the Note
                  shall be due and payable on November 15, 2009.

Interest,  computed on the unpaid balance of the Note,  shall be due and payable
monthly as it accrues, on the same dates as, but in addition to each installment
of principal."

3.  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 Modification  Agreement shall in no
manner  vitiate,  affect or impair the Note or the Liens  (except  as  expressly
modified in this  Modification  Agreement)  and that such Liens shall not in any
manner be waived, released, altered or modified.

4. 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  Modification
                  Agreement  and the  terms  of the Note or of the  Liens,  this
                  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 Modification Agreement.

         (c)      Any default by Borrower in the  performance of his 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  Modification
                  Agreement, waive any rights it may have against any person not
                  a party hereto.

<PAGE>

         (e)      All terms, provisions,  covenants,  agreements, and conditions
                  of the Note and the Liens are  unchanged,  except as  provided
                  herein.  Borrower agrees that this 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  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.

                                    Borrower:
                                    ---------

                                    Natural Gas Services Group, Inc.

                                    By:_________________________________________
                                       Wallace C. Sparkman, President

                                    Lender:
                                    -------

                                    Western National Bank

                                    By:_________________________________________
                                       Scott A. Lovett, Executive Vice President

<PAGE>

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

         This instrument was acknowledged  before me on December _____, 2004, by
Wallace C. Sparkman,  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 December _____, 2004, 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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