UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


                                    FORM 8-K


                 CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d)
                     OF THE SECURITIES EXCHANGE ACT OF 1934


         Date of Report (Date of earliest event reported): May 10, 2005


                        NATURAL GAS SERVICES GROUP, INC.
             (Exact Name of Registrant as Specified in Its Charter)



              Colorado                      1-31398               75-2811855
  (State or other jurisdiction          (Commission File        (IRS Employer
of  Incorporation or organization)          Number)          Identification No.)


2911 South County Road 1260 Midland, Texas                         79706
 (Address of Principal Executive Offices)                        (Zip Code)


                                  432-563-3974
              (Registrant's telephone number, including area code)


                                 Not Applicable
          (Former name or former address, if changed since last report)


Check  the  appropriate  box  below  if the  Form  8-K  filing  is  intended  to
simultaneously  satisfy the filing obligation of the registrant under any of the
following provisions:

[_]      Written  communications  pursuant to Rule 425 under the  Securities Act
         (17 CFR 230.425)

[_]      Soliciting  material pursuant to Rule 14a-12 under the Exchange Act (17
         CFR 240.14a-12)

[_]      Pre-commencement  communications  pursuant to Rule  14d-2(b)  under the
         Exchange Act (17 CFR 240.14d-2(b))

[_]      Pre-commencement  communications  pursuant to Rule  13e-4(c)  under the
         Exchange Act (17 CFR 240.13e-4(c))


Item 1.01. Entry into a Material Definitive Agreement. On May 10, 2005, Natural Gas Services Group, Inc., as borrower, and Western National Bank, as lender, entered into a First Modification to Fourth Amended and Restated Loan Agreement, dated effective as of May 1, 2005 (the "Loan Modification Agreement"). The Loan Modification Agreement amends the "Consolidated Current Ratio" definition in the Fourth Amended and Restated Loan Agreement, dated March 14, 2005 (the "Loan Agreement"), between Natural Gas and Western National Bank, by expanding the assets considered in the calculation of such ratio to include restricted cash held by Natural Gas. In addition, under the Loan Modification Agreement, we are required to maintain a Consolidated Current Ratio of 1.4 to 1.00 from month to month, versus 1.5 to 1.00 as originally required under the Loan Agreement. As previously reported, the indebtedness extended to Natural Gas by Western National Bank under the Loan Agreement is evidenced by the following promissory notes (collectively, the "Notes"): (1) Multiple Advance Term Promissory Note, dated March 14, 2005, in the original principal amount of $1,500,000.00, payable by Natural Gas Services Group, Inc. to the order of Western National Bank, bearing interest at a current annual rate of 7.00%and maturing on April 1, 2010 (the "$1,500,000.00 Multiple Advance Term Note"); (2) Multiple Advance Term Promissory Note, dated March 14, 2005, in the original principal amount of $10,000,000.00, payable by Natural Gas Services Group, Inc. to the order of Western National Bank, bearing interest at a current annual rate of 7.00% and maturing on April 1, 2011 ($10,000,000.00 Multiple Advance Term Note"); (3) Term Promissory Note, dated January 3, 2005, in the original principal amount of $8,000,000.00, payable by Natural Gas Services Group, Inc. to the order of Western National Bank, bearing interest at a current annual rate of 7.00% and maturing on January 1, 2012 ("the $8,000,000.00 Term Note"); (4) Revolving Line of Credit Promissory Note, dated January 3, 2005, in the original principal amount of $2,000,000.00, payable by Natural Gas Services Group, Inc. to the order of Western National Bank, bearing interest at a current annual rate of 7.00% and maturing on January 1, 2006 (the "Revolving Line of Credit Note"); (5) Term Promissory Note, dated November 3, 2003, in the original principal amount of $7,521,109.00, payable by Natural Gas Services Group, Inc. to the order of Western National Bank, bearing interest at a current annual rate of 7.00% and maturing on September 15, 2007, as modified in a Modification Agreement, dated January 3, 2005 (the "$7,521,109.00 Term Note"); (6) Advancing Line of Credit Promissory Note, dated November 3, 2003, in the original principal amount of $10,000,000.00, payable by Natural Gas Services Group, Inc. to the order of Western National Bank, bearing interest at a current annual rate of 7.00% and maturing on November 15, 2009, as modified in a Modification Agreement, dated December 15, 2004 (the "Advancing Line of Credit Note"); and

(7) Term Promissory Note, dated January 3, 2005, in the original principal amount of $1,415,836.00, payable by Screw Compression Systems, Inc. to the order of Western National Bank, bearing interest at a current annual rate of 7.00% and maturing on January 1, 2010 (the $1,415,836,00 Term Note"). Concurrently with the our execution and delivery of the Loan Modification Agreement, we also entered into the following note modification agreements (collectively, the "Note Modification Agreements"): (1) Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank, modifying the $1,500,000.00 Multiple Advance Term Note; (2) Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank, modifying the $10,000,000.00 Multiple Advance Term Note; (3) Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank, modifying the $8,000,000.00 Term Note; (4) Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank, modifying the Revolving Line of Credit Note; (5) Second Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank, modifying the $7,521,109.00 Term Note; (6) Second Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank, modifying the Advancing Line of Credit Note; and (7) Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank, modifying the $1,415,836.00 Term Note. Under the Note Modification Agreements, the annual rate at which each Note bears interest was reduced by 0.50%, and with the exception of the $7,521,109.00 Term Note and the Advancing Line of Credit Note, the floor rate of each Note was reduced from 6.25% to 6.00%. The floor rate of the $7,521,109.00 Term Note and the Advancing Line of Credit Note remains at 5.25%. The remaining terms and provisions of the Loan Agreement and the Notes remain in full force and effect.

Item 9.01 Financial Statements and Exhibits. (c) Exhibits. Exhibit No. Description ----------- ----------- *10.1 First Modification to Fourth Amended and Restated Loan Agreement, dated effective as of May 1, 2005, by and among Natural Gas Services Group, Inc. and Western National Bank. *10.2 Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank. *10.3 Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank. *10.4 Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank. *10.5 Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank. *10.6 Second Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank. *10.7 Second Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank. *10.8 Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank. --------------------- * Filed herewith

SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized. NATURAL GAS SERVICES GROUP, INC. By: /s/ Stephen C. Taylor ----------------------------- Stephen C. Taylor, President Dated: May 10, 2005

EXHIBIT INDEX Exhibit No. Description - ----------- ----------- *10.1 First Modification to Fourth Amended and Restated Loan Agreement, dated effective as May 1, 2005, by and among Natural Gas Services Group, Inc. and Western National Bank. *10.2 Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank. *10.3 Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank. *10.4 Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank. *10.5 Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank. *10.6 Second Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank. *10.7 Second Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank. *10.8 Modification Agreement, dated effective as of May 1, 2005, by and between Natural Gas Services Group, Inc. and Western National Bank. - --------------------- * Filed herewith

Exhibit 10.1

                              FIRST MODIFICATION TO
                           FOURTH AMENDED AND RESTATED
                                 LOAN AGREEMENT

         This First  Modification  to Fourth Amended and Restated Loan Agreement
(the "First  Modification")  is made and entered into  effective May 1, 2005, by
and among  Natural Gas Services  Group,  Inc.  ("Borrower"),  Screw  Compression
Systems, Inc. ("Guarantor"), and Western National Bank ("Lender")

                                    RECITALS

         WHEREAS,  Borrower,  Guarantor,  and Lender  entered  into that certain
Fourth  Amended  and  Restated  Loan  Agreement  dated March 14, 2005 (the "Loan
Agreement"); and

         WHEREAS,  Borrower  ,  Guarantor,  and  Lender now desire to modify the
definition of "Consolidated  Current Ratio" as set out in the Loan Agreement 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, Guarantor, 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:

         "Consolidated  Current  Ratio"  means  the  ratio of (i) the sum of the
         current assets and restricted cash of the Borrower and its Subsidiaries
         to (ii) the sum of the  current  liabilities  of the  Borrower  and its
         Subsidiaries, all determined on a consolidated basis."

2.       Paragraph 6.1(a) Consolidated Current Ratio is amended in the following
         respects:

         "(a) Consolidated Current Ratio. Permit the Consolidated Current Ratio,
         as defined  herein and calculated  pursuant to Exhibit S hereto,  to be
         less than 1.4 to 1.0 as of February 28, 2005, and as of the end of each
         month thereafter."






                                                                               1

3. Exhibit S - Consolidated Current Ratio Calculation, Paragraph 1 is amended in the following respects: "1. Sum of current assets and restricted cash of Borrower and its consolidated Subsidiaries" ARTICLE 2 Miscellaneous ------------- 1. The provisions of this First Modification to Fourth 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. The Loan Agreement, as amended herein, is hereby ratified, adopted and confirmed by Borrower and the Guarantor. Each agreement, representation, warranty and covenant made by Borrower and Guarantor in the Loan Agreement is hereby ratified, adopted, and confirmed by Borrower and Guarantor on the date of execution hereof. 3. The effective date of this First Modification to Fourth Amended and Restated Loan Agreement shall be May 1, 2005, at which time the provisions of this First Modification to Fourth 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 May 5, 2005, but effective as of May 1, 2005. BORROWER: --------- Natural Gas Services Group, Inc. By: /s/ Stephen C. Taylor --------------------------------------- Stephen C. Taylor, President 2

GUARANTOR: ---------- Screw Compression Systems, Inc. By /s/ Paul D. Hensley ---------------------------------------- Paul D. Hensley, President LENDER: ------- Western National Bank By /s/ Scott A. Lovett ---------------------------------------- Scott A. Lovett, Executive Vice President 3

Exhibit 10.2

                                        $1,500,000.00 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
$1,500,000.00,  bearing interest at the rate stated therein, with a stated final
maturity  date of April 1, 2010 (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 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."




                                                                               1

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 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 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 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 AGREE MENTS OF THE PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES. 2

Borrower: --------- Natural Gas Services Group, Inc. By: /s/ Stephen C. Taylor ---------------------------------------- Stephen C. Taylor, President Lender: ------- Western National Bank By /s/ Scott A. Lovet ----------------------------------------- Scott A. Lovett, Executive Vice President STATE OF TEXAS ss. ss. COUNTY OF MIDLAND ss. This instrument was acknowledged before me on May 10, 2005, by Stephen C. Taylor, President of Natural Gas Services Group, Inc., a Colorado corporation, on behalf of said corporation. /s/ Deborah K. Tullos ----------------------------------------- Notary Public, State of Texas STATE OF TEXAS ss. ss. COUNTY OF MIDLAND ss. This instrument was acknowledged before me on May 11, 2005, by Scott A. Lovett, Executive Vice President of Western National Bank, a national banking association, on behalf of said association. /s/ Deborah K. Tullos ----------------------------------------- Notary Public, State of Texas 3

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 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."




                                                                               1

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 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 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 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 AGREE MENTS OF THE PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES. 2

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 May 10, 2005, by Stephen C. Taylor, President of Natural Gas Services Group, Inc., a Colorado corporation, on behalf of said corporation. /s/ Deborah K. Tullos ----------------------------------------- Notary Public, State of Texas STATE OF TEXAS ss. ss. COUNTY OF MIDLAND ss. This instrument was acknowledged before me on May 11, 2005, by Scott A. Lovett, Executive Vice President of Western National Bank, a national banking association, on behalf of said association. /s/ Deborah K. Tullos ----------------------------------------- Notary Public, State of Texas 3

Exhibit 10.4

                                                         $8,000,000.00 Term Note
                                                           dated January 3, 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 January 3, 2005,  Borrower executed and delivered to Lender that certain Term
Promissory Note in the original principal sum of $8,000,000.00, bearing interest
at the rate stated therein, with a stated final maturity date of January 1, 2012
(the "Note"), pursuant to that certain Third Amended and Restated Loan Agreement
dated  January 3, 2005,  and  subsequently  amended and restated in 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 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."

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 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."





                                                                               1

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 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 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 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 AGREE MENTS OF THE PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES. 2

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 May 10, 2005, by Stephen C. Taylor, President of Natural Gas Services Group, Inc., a Colorado corporation, on behalf of said corporation. /s/ Deborah K. Tullos ----------------------------------------- Notary Public, State of Texas STATE OF TEXAS ss. ss. COUNTY OF MIDLAND ss. This instrument was acknowledged before me on May 11, 2005, by Scott A. Lovett, Executive Vice President of Western National Bank, a national banking association, on behalf of said association. /s/ Deborah K. Tullos ----------------------------------------- Notary Public, State of Texas 3

Exhibit 10.5

                                                      Revolving Line Credit Note
                                                           dated January 3, 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 January 3, 2005,  Borrower  executed  and  delivered  to Lender that  certain
Revolving  Line of  Credit  Promissory  Note in the  original  principal  sum of
$2,000,000.00,  bearing interest at the rate stated therein, with a stated final
maturity  date of January 1, 2006 (the  "Note"),  pursuant to that certain Third
Amended and Restated  Loan  Agreement  dated  January 3, 2005,  as  subsequently
amended and restated in 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 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."

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 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."





                                                                               1

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 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 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 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 AGREE MENTS OF THE PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES. 2

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 May 10, 2005, by Stephen C. Taylor, President of Natural Gas Services Group, Inc., a Colorado corporation, on behalf of said corporation. /s/ Deborah K. Tullos ----------------------------------------- Notary Public, State of Texas STATE OF TEXAS ss. ss. COUNTY OF MIDLAND ss. This instrument was acknowledged before me on May 11, 2005, by Scott A. Lovett, Executive Vice President of Western National Bank, a national banking association, on behalf of said association. /s/ Deborah K. Tullos ----------------------------------------- Notary Public, State of Texas 3

Exhibit 10.6

                                                         $7,521,109.00 Term Note
                                                          dated November 3, 2003


                          SECOND MODIFICATION AGREEMENT

This  Second  Modification   Agreement  ("Second  Modification   Agreement")  is
effective as of May 1, 2005.  The parties to the Second  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 Term
Promissory Note in the original principal sum of $7,521,109.00, bearing interest
at the rate stated  therein,  with a stated final maturity date of September 15,
2007, as modified in Modification  Agreement dated January 3, 2005 (the "Note").
The Note was made  pursuant to that certain  Second  Amended and  Restated  Loan
Agreement dated November 3, 2003, as  subsequently  amended and restated in that
certain  Third Amended and Restated Loan  Agreement  dated January 3, 2005,  and
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 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 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) five and one-quarter  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."

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 in
         effect from day to day, or (ii) five and one- quarter 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."





                                                                               1

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. 2

THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES. 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 May 10, 2005, by Stephen C. Taylor, President of Natural Gas Services Group, Inc., a Colorado corporation, on behalf of said corporation. /s/ Deborah K. Tullos ----------------------------------------- Notary Public, State of Texas STATE OF TEXAS ss. ss. COUNTY OF MIDLAND ss. This instrument was acknowledged before me on May 11, 2005, by Scott A. Lovett, Executive Vice President of Western National Bank, a national banking association, on behalf of said association. /s/ Deborah K. Tullos ----------------------------------------- Notary Public, State of Texas 3

Exhibit 10.7

                                                   Advancing Line of Credit Note
                                                          dated November 3, 2003


                          SECOND MODIFICATION AGREEMENT

This  Second  Modification   Agreement  ("Second  Modification   Agreement")  is
effective as of May 1, 2005.  The parties to the Second  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, as modified in Modification  Agreement dated
December  15, 2004 (the  "Note").  The Note was made  pursuant  to that  certain
Second  Amended  and  Restated  Loan  Agreement   dated  November  3,  2003,  as
subsequently  amended and  restated in that certain  Third  Amended and Restated
Loan  Agreement  dated  January 3, 2005,  and 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 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 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, as modified
in Modification Agreement dated December 15, 2004:

                  "...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-quarter  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."

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 in
         effect from day to day, or (ii) five and one- quarter 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."




                                                                               1

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. 2

THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES. 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 May 10, 2005, by Stephen C. Taylor, President of Natural Gas Services Group, Inc., a Colorado corporation, on behalf of said corporation. /s/ Deborah K. Tullos ----------------------------------------- Notary Public, State of Texas STATE OF TEXAS ss. ss. COUNTY OF MIDLAND ss. This instrument was acknowledged before me on May 11, 2005, by Scott A. Lovett, Executive Vice President of Western National Bank, a national banking association, on behalf of said association. /s/ Deborah K. Tullos ----------------------------------------- Notary Public, State of Texas 3

Exhibit 10.8

                                                         $1,415,836.00 Term Note
                                                           dated January 3, 2005


                             MODIFICATION AGREEMENT

This Modification Agreement ("Modification Agreement") is effective as of May 1,
2005. The parties to the Modification  Agreement are Screw Compression  Systems,
Inc. ("Borrower") and Western National Bank ("Lender").

                                    RECITALS

On January 3, 2005,  Borrower executed and delivered to Lender that certain Term
Promissory Note in the original principal sum of $1,415,836.00, bearing interest
at the rate stated therein, with a stated final maturity date of January 1, 2010
(the "Note"), pursuant to that certain Third Amended and Restated Loan Agreement
dated January 3, 2005 (the "Prior Loan  Agreement"),  as amended and restated in
that certain  Fourth  Amended and Restated Loan  Agreement  dated March 15, 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 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."

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 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."






                                                                               1

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 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 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 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 AGREE MENTS OF THE PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES. 2

Borrower: --------- Screw Compression Systems, Inc. By: /s/ Paul D. Hensley ---------------------------------------- Paul D. Hensley, President Lender: ------- Western National Bank By /s/ Scott A. Lovet ----------------------------------------- Scott A. Lovett, Executive Vice President STATE OF OKLAHOMA ss. ss. COUNTY OF ROGERS ss. This instrument was acknowledged before me on May 10, 2005, by Paul D. Hensley, President of Screw Compression Systems, Inc., a Texas corporation, on behalf of said corporation. Notary Public, State of Oklahoma Printed Name: Deborah K. Tullos ---------------------------- Commission Expires: August 17, 2005 ---------------------- STATE OF TEXAS ss. ss. COUNTY OF MIDLAND ss. This instrument was acknowledged before me on May 11, 2005, by Scott A. Lovett, Executive Vice President of Western National Bank, a national banking association, on behalf of said association. /s/ Deborah K. Tullos ----------------------------------------- Notary Public, State of Texas 3