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

                                    AMENDED
                                  SCHEDULE 13G

                   UNDER THE SECURITIES EXCHANGE ACT OF 1934

                               (AMENDMENT NO. 01)*

                        Natural Gas Services Group, Inc.
--------------------------------------------------------------------------------
                                (Name of Issuer)

                         Common Stock ($.01 Par Value)
--------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                   63886Q109
                 ---------------------------------------------
                                 (CUSIP Number)

February 14, 2005, The Date Upon Which The Beneficial Owner Ceased To Be The
Beneficial Owner of Five Percent (5%) Of The Class Of Securities Of The Issuer
And The Date Upon Which A Yearly Amendment Is Required
--------------------------------------------------------------------------------
            (Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule
is filed:

     [ ] Rule 13d-1(b)

     [X] Rule 13d-1(c)

     [ ] Rule 13d-1(d)

* The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter the
disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).


PERSONS WHO RESPOND TO THE COLLECTION OF INFORMATION CONTAINED IN THIS FORM ARE
NOT REQUIRED TO RESPOND UNLESS THE FORM DISPLAYS A CURRENTLY VALID OMB CONTROL
NUMBER.

SEC 1745 (12-02)               Page 1 of 6 pages




CUSIP No. 63886Q109
--------------------------------------------------------------------------------

     1.  Names of Reporting Persons.  Howard Kirk Mehaffey
         I.R.S. Identification Nos. of above persons (entities only).

--------------------------------------------------------------------------------

     2.  Check the Appropriate Box if a Member of a Group (See Instructions)

         (a) Not Applicable

         (b)
--------------------------------------------------------------------------------

     3.  SEC Use Only
--------------------------------------------------------------------------------

     4.  Citizenship or Place of Organization  U.S.A.
--------------------------------------------------------------------------------

Number of     5. Sole Voting Power See The Attached Response to Rows (5-11)
Shares Bene-  ------------------------------------------------------------------
ficially by   6. Shared Voting Power
Owned by Each ------------------------------------------------------------------
Reporting     7. Sole Dispositive Power
Person With:  ------------------------------------------------------------------
              8. Shared Dispositive Power
--------------------------------------------------------------------------------

     9.  Aggregate Amount Beneficially Owned by Each Reporting Person

     10. Check if the Aggregate Amount in Row (9) Excludes Certain Shares
         (See Instructions)

     11. Percent of Class Represented by Amount in Row (9)  Not Applicable
--------------------------------------------------------------------------------

     12. Type of Reporting Person (See Instructions)
--------------------------------------------------------------------------------
         Individual (IN) In His Capacity As The Sole Managing Partner Of
         CAV-RDV, Ltd., A Texas Limited Partnership
--------------------------------------------------------------------------------


                               Page 2 of 6 pages


                 RESPONSE TO ROWS 5-11 OF AMENDED SCHEDULE 13G

         From October 21, 2002, the Date of the Event Which Required the
Original Filing of Schedule 13G by the Beneficial Owner of the Class of
Securities of the Issuer, until June 1, 2004, no transactions were effected by
the Beneficial Owner of the Shares of the Class of Securities of the Issuer.
From June 1, 2002, until July 21, 2004, 97,000 Shares of the Class of Securities
of the Issuer (as reported in the Original Filing of Schedule 13G by the
Beneficial Owner of such Shares) were sold in five (5) separate open market
transactions. From said July 21, 2004, until December 31, 2004, no further
transactions were effected by the Beneficial Owner in the Shares of the Class of
Securities of the Issuer. From December 31, 2004, until February 14, 2005,
75,000 Shares of the Class of Securities of the Issuer were sold in a series of
multiple open market transactions. With respect to Rows 5-11 of this Amended
Schedule 13G, the following information is listed with respect to Shares of the
Class of Securities of the Issuer Beneficially Owned by the Reporting Person as
of July 21, 2004, the last date referenced in the Original Filing of Schedule
13G, and as of February 14, 2005, the date of this Amended Schedule 13G Filing,
the date upon which the Beneficial Owner ceased to be the Beneficial Owner five
percent (5%) or more of the Shares of the Class of Securities of the Issuer and
which otherwise caused the Filing of this Amended Schedule 13G.

         With Respect to Shares Beneficially Owned by the Reporting Person as of
July 21, 2004, the last date referenced in the Original Filing of Schedule 13G
by the Beneficial Owner, the Following Information is Applicable:


     5.   Sole Voting Power: 373,250

     6.   Shared Voting Power: 0

     7.   Sole Dispositive Power: 373,250

     8.   Shared Dispositive Power: 0

     9.   Aggregate Amount Beneficially Owned by Each Reporting Person: 373,250

     10.  Check if the Aggregate Amount in Row (9) Excludes Certain Shares. N.A.

     11.  Percent of Class Represented in Row (9): 6.2%

         With Respect to Shares Beneficially Owned by the Reporting Person as of
February 14, 2005, the date upon which the Beneficial Owner ceased to be the
Beneficial Owner of five percent (5%) or More of the Shares of the Class of
Securities of the Issuer Causing the Filing of this Amended Schedule 13G, the
Following Information is Applicable:

     5.   Sole Voting Power: 298,250




     6.   Shared Voting Power: 0

     7.   Sole Dispositive Power: 298,250

     8.   Shared Dispositive Power: 0

     9.   Aggregate Amount Beneficially Owned by Each Reporting Person: 298,250

     10.  Check if the Aggregate Amount in Row (9) Excludes Certain Shares. N.A.

     11.  Percent of Class Represented in Row (9): 4.9%




                         INSTRUCTIONS FOR SCHEDULE 13G



INSTRUCTIONS FOR COVER PAGE

(1)  Names and I.R.S. Identification Numbers of Reporting Persons--Furnish the
     full legal name of each person for whom the report is filed--i.e., each
     person required to sign the schedule itself--including each member of a
     group. Do not include the name of a person required to be identified in the
     report but who is not a reporting person. Reporting persons that are
     entities are also requested to furnish their I.R.S. identification numbers,
     although disclosure of such numbers if voluntary, not mandatory (see
     "SPECIAL INSTRUCTIONS FOR COMPLYING WITH SCHEDULE 13G" below).

(2)  If any of the shares beneficially owned by a reporting person are held as a
     member of a group and that membership is expressly affirmed, please check
     row 2(a). If the reporting person disclaims membership in a group or
     describes a relationship with other persons but does not affirm the
     existence of a group, please check row 2(b) [unless it is a joint filing
     pursuant to Rule 13d-1(k)(1) in which case it may not be necessary to check
     row 2(b)].

(3)  The third row is for SEC internal use; please leave blank.

(4)  Citizenship or Place of Organization--Furnish citizenship if the named
     reporting person is a natural person. Otherwise, furnish place of
     organization.

(5)-(9), (11) Aggregate Amount Beneficially Owned By Each Reporting Person,
     Etc.--Rows (5) through (9) inclusive, and (11) are to be completed in
     accordance with the provisions of Item 4 of Schedule 13G. All percentages
     are to be rounded off to the nearest tenth (one place after decimal point).

(10) Check if the aggregate amount reported as beneficially owned in row (9)
     does not include shares as to which beneficial ownership is disclaimed
     pursuant to Rule 13d-4 (17 CFR 240.13d-4) under the Securities Exchange Act
     of 1934.

(12) Type of Reporting Person--Please classify each "reporting person" according
     to the following breakdown (see Item 3 of Schedule 13G) and place the
     appropriate symbol on the form:




          Category                                   Symbol
                                                  

          Broker Dealer                              BD
          Bank                                       BK
          Insurance Company                          IC
          Investment Company                         IV
          Investment Adviser                         IA
          Employee Benefit Plan, Pension Fund,
               or Endowment Fund                     EP
          Parent Holding Company/Control Person      HC
          Savings Association                        SA
          Church Plan                                CP
          Corporation                                CO
          Partnership                                PN
          Individual                                 IN
          Other                                      OO



Notes:

     Attach as many copies of the second part of the cover page as are needed,
one reporting person per page.

     Filing persons may, in order to avoid unnecessary duplication, answer
items on the schedules (Schedule 13D, 13G or 14D-1) by appropriate cross
references to an item or items on the cover page(s). This approach may only be
used where the cover page item or items provide all the disclosure required by
the schedule item. Moreover, such a use of a cover page item will result in the
item becoming a part of the schedule and accordingly being considered as
"filed" for purposes of Section 18 of the Securities Exchange Act or otherwise
subject to the liabilities of that section of the Act.

     Reporting persons may comply with their cover page filing requirements by
filing either completed copies of the blank forms available from the Commission,
printed or typed facsimiles, or computer printed facsimiles, provided the
documents filed have identical formats to the forms prescribed in the
Commission's regulations and meet existing Securities Exchange Act rules as to
such matters as clarity and size (Securities Exchange Act Rule 12b-12).

              SPECIAL INSTRUCTIONS FOR COMPLYING WITH SCHEDULE 13G

     Under Sections 13(d), 13(g), and 23 of the Securities Exchange Act of 1934
and the rules and regulations thereunder, the Commission is authorized to
solicit the information required to be supplied by this schedule by certain
security holders of certain issuers.



                               Page 3 of 6 pages


     Disclosure of the information specified in this schedule is mandatory,
except for I.R.S. identification numbers, disclosure of which is voluntary. The
information will be used for the primary purpose of determining and disclosing
the holdings of certain beneficial owners of certain equity securities. This
statement will be made a matter of public record. Therefore, any information
given will be available for inspection by any member of the public.

     Because of the public nature of the information, the Commission can use it
for a variety of purposes, including referral to other governmental authorities
or securities self-regulatory organizations for investigatory purposes or in
connection with litigation involving the Federal securities laws or other
civil, criminal or regulatory statutes or provisions. I.R.S. identification
numbers, if furnished, will assist the Commission in identifying security
holders and, therefore, in promptly processing statements of beneficial
ownership of securities.

     Failure to disclose the information requested by this schedule, except for
I.R.S. identification numbers, may result in civil or criminal action against
the persons involved for violation of the Federal securities laws and rules
promulgated thereunder.

                              GENERAL INSTRUCTIONS

A.   Statements filed pursuant to Rule 13d-1(b) containing the information
     required by this schedule shall be filed not later than February 14
     following the calendar year covered by the statement or within the time
     specified in Rules 13d-1(b)(2) and 13d-2(c). Statements filed pursuant to
     Rule 13d-1(c) shall be filed within the time specified in Rules 13d-1(c),
     13d-2(b) and 13d-2(d). Statements filed pursuant to Rule 13d-1(d) shall be
     filed not later than February 14 following the calendar year covered by the
     statement pursuant to Rules 13d-1(d) and 13d-2(b).

B.   Information contained in a form which is required to be filed by rules
     under section 13(f)(15 U.S.C. 78m(f)) for the same calendar year as that
     covered by a statement on this schedule may be incorporated by reference in
     response to any of the items of this schedule. If such information is
     incorporated by reference in this schedule, copies of the relevant pages of
     such form shall be filed as an exhibit to this schedule.

C.   The item numbers and captions of the items shall be included but the text
     of the items is to be omitted. The answers to the items shall be so
     prepared as to indicate clearly the coverage of the items without referring
     to the text of the items. Answer every item. If an item is inapplicable or
     the answer is in the negative, so state.

ITEM 1.

     (a) Name of Issuer
               Natural Gas Services Group, Inc.

     (b) Address of Issuer's Principal Executive Offices
               2911 South County Road 1260
               Midland, Texas 79706

ITEM 2.

     (a) Name of Person Filing
               Howard Kirk Mehaffey

     (b) Address of Principal Business Office or, if none, Residence
               5602 Camden
               Midland, Texas 79707

     (c) Citizenship


     (d) Title of Class of Securities
               Common Stock ($.01 Par Value)

     (e) CUSIP Number
               63886Q109

ITEM 3. IF THIS STATEMENT IS FILED PURSUANT TO SECTIONS 240.13d-1(b) OR
240.13d-2(b) OR (c), CHECK WHETHER THE PERSON FILING IS A:

     (a) [ ] Broker or dealer registered under section 15 of the Act
             (15 U.S.C. 78o).

     (b) [ ] Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).

     (c) [ ] Insurance company as defined in section 3(a)(19) of the Act
             (15 U.S.C. 78c).

     (d) [ ] Investment company registered under section 8 of the Investment
             Company Act of 1940 (15 U.S.C. 80a-8).

     (e) [ ] An investment adviser in accordance with Section
             240.13d-1(b)(1)(ii)(E);

     (f) [ ] An employee benefit plan or endowment fund in accordance with
             Section 240.13d-1(b)(1)(ii)(F);

     (g) [ ] A parent holding company or control person in accordance with
             Section 240.13d-1(b)(1)(ii)(G);

     (h) [ ] A savings associations as defined in Section 3(b) of the Federal
             Deposit Insurance Act (12 U.S.C. 1813);

     (i) [ ] A church plan that is excluded from the definition of an
             investment company under section 3(c)(14) of the Investment Company
             Act of 1940 (15 U.S.C. 80a-3);

                               Page 4 of 6 pages


     (j) [ ] Group, in accordance with Section 240.13d-1(b)(1)(ii)(J).

ITEM 4. OWNERSHIP. See the Attached Responses to Item 4.

     Provide the following information regarding the aggregate number and
percentage of the class of securities of the issuer identified in Item 1.

     (a) Amount beneficially owned: _______.

     (b) Percent of class: _______.

     (c) Number of shares as to which the person has:

          (i)   Sole power to vote or to direct the vote _______.

          (ii)  Shared power to vote or to direct the vote _______.

          (iii) Sole power to dispose or to direct the disposition of _______.

          (iv)  Shared power to dispose or to direct the disposition of _______.

     Instruction. For computations regarding securities which represent a right
to acquire an underlying security see Section 240.13d-3(d)(1).

ITEM 5. OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS 

     If this statement is being filed to report the fact that as of the date
hereof the reporting person has ceased to be the beneficial owner of more than
five percent of the class of securities, check the following [X].

Instruction: Dissolution of a group requires a response to this item.

ITEM 6. OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON.

     See The Attached Response To Item 6.

     If any other person is known to have the right to receive or the power to
direct the receipt of dividends from, or the proceeds from the sale of, such
securities, a statement to that effect should be included in response to this
item and, if such interest relates to more than five percent of the class, such
person should be identified. A listing of the shareholders of an investment
company registered under the Investment Company Act of 1940 or the beneficiaries
of employee benefit plan, pension fund or endowment fund is not required.

ITEM 7. IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE
        SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY Not Applicable

     If a parent holding company has filed this schedule, pursuant to Rule
13d-1(b)(ii)(G), so indicate under Item 3(g) and attach an exhibit stating the
identity and the Item 3 classification of the relevant subsidiary. If a parent
holding company has filed this schedule pursuant to Rule 13d-1(c) or Rule
13d-1(d), attach an exhibit stating the identification of the relevant
subsidiary.

ITEM 8. IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP Not Applicable

     If a group has filed this schedule pursuant to Section
240.13d-1(b)(1)(ii)(J), so indicate under Item 3(j) and attach an exhibit
stating the identity and Item 3 classification of each member of the group. If a
group has filed this schedule pursuant to Section 240.13d-1(c) or Section
240.13d-1(d), attach an exhibit stating the identity of each member of the
group.

ITEM 9. NOTICE OF DISSOLUTION OF GROUP Not Applicable

     Notice of dissolution of a group may be furnished as an exhibit stating the
date of the dissolution and that all further filings with respect to
transactions in the security reported on will be filed, if required, by members
of the group, in their individual capacity. See Item 5.

ITEM 10. CERTIFICATION


                               Page 5 of 6 pages


                 RESPONSE TO ITEM 4. OWNERSHIP OF SCHEDULE 13G

         From October 21, 2002, the Date of the Event Which Required the
Original Filing of Schedule 13G, until June 1, 2004, no transactions were
effected by the Beneficial Owner in the Shares of the Class of Securities of the
Issuer. From June 1, 2004, until July 21, 2004, 97,000 Shares of the Class of
Securities of the Issuer (as reported in the Original Filing of Schedule 13G)
were sold in five (5) separate open market transactions. From said July 21,
2004, until December 31, 2004, no further transactions were effected by the
Beneficial Owner in the Shares of the Class of Securities of the Issuer. From
December 31, 2004, until February 14, 2005, 75,000 Shares of the Class of
Securities of the Issuer were sold in a series of multiple open market
transactions. With respect to Item 4. Ownership, of this Amended Schedule 13G,
the following information is listed with respect to Shares of the Class of
Securities Beneficially Owned by the Reporting Person as of July 21, 2004, the
last date referenced in the Original Filing of Schedule 13G, and as of February
14, 2005, the date of this Amended Schedule 13G Filing, the date upon which the
Beneficial Owner ceased to be the Beneficial Owner of five percent (5%) or more
of the Shares of the Class of Securities of the Issuer and which otherwise
caused the Filing of this Amended Schedule 13G.

         With Respect to the Shares Beneficially Owned by the Reporting Person
as of July 21, 2004, the Last Date Referenced in the Original Filing of Schedule
13G by the Beneficial Owner, the Following Information is Applicable: 

          (a) Amount beneficially owned: 373,250

          (b) Percent of class: 6.2%

          (c) Number of shares as to which the person has:

               (i)   Sole power to vote or to direct the vote: 373,250

               (ii)  Shared power to vote or to direct the vote: 0

               (iii) Sole power to dispose or to direct the disposition of:
                     373,250

               (iv)  Shared power to dispose or to direct the disposition of: 0

         With Respect to the Shares Beneficially Owned by the Reporting Person
as of February 14, 2004, the Date upon which the Beneficial Owner Ceased to be
the Beneficial Owner of Five Percent (5%) or More of the Shares of the Class of
Securities of the Issuer Causing the Filing of this Amended Schedule 13G, the
Following Information is Applicable:

          (a) Amount beneficially owned: 298,250



          (b) Percent of class: 4.9%

          (c) Number of shares as to which the person has:

               (i)   Sole power to vote or direct the vote: 298,250

               (ii)  Shared power to vote or direct the vote: 0

               (iii) Sole power to dispose or to direct the disposition of:
                     298,250

               (iv)  Shared power to dispose or to direct the disposition of: 0


           RESPONSE TO ITEM 6. OF AMENDED SCHEDULE 13G: OWNERSHIP OF
               MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON

         The Original Schedule 13G Filing, was made by Howard Kirk Mehaffey, the
Reporting Person and the Beneficial Owner of the Shares of the Class of
Securities of the Issuer reported on in said Original Schedule 13G Filing and
also reported on in this Amended Schedule 13G Filing. The Filings were and are
made by Howard Kirk Mehaffey in his capacity as the Sole Managing General
Partner of CAV-RDV, Ltd., a Texas Limited Partnership. In such capacity, Howard
Kirk Mehaffey has the sole power to direct the receipt of dividends or the
proceeds from the sale of such Securities to himself, as the Sole Managing
General Partner, and to Candice A. Vinson and Ryan D. Vinson as the Limited
Partners of CAV-RDV, Ltd., in accordance with the Partner's respective
Partnership Interests as set forth in the Agreement of Limited Partnership
between the Parties. Such Interests, in their totality, represent the Shares
reported on in the Original Filing Schedule 13G and this Amended Filing of
Schedule 13G of which Howard Kirk Mehaffey is the Beneficial Owner and as
represented in the Original Filing (both prior to and after taking in to account
the effect of certain transactions with respect to such Shares as reported on in
such Original Filing) more than five percent (5%) of the Issuer's outstanding
Shares of the Class of Securities and which, as reported in this Amended Filing
after taking in to effect certain transactions as reported in such Amended
Schedule 13G Filing, represents less than five (5%) of such Shares and which
otherwise caused the Filing of this Amended Schedule 13G to be made.



(a)  The following certification shall be included if the statement is filed
     pursuant to Section 240.13d-1(b):

          By signing below I certify that, to the best of my knowledge and
          belief, the securities referred to above were acquired and are held in
          the ordinary course of business and were not acquired and are not held
          for the purpose of or with the effect of changing or influencing the
          control of the issuer of the securities and were not acquired and are
          not held in connection with or as a participant in any transaction
          having that purpose or effect.

(b)  The following certification shall be included if the statement is filed
     pursuant to Section 240.13d-1(c):

(X)       By signing below I certify that, to the best of my knowledge and
          belief, the securities referred to above were not acquired and are not
          held for the purpose of or with the effect of changing or influencing
          the control of the issuer of the securities and were not acquired and
          are not held in connection with or as a participant in any transaction
          having that purpose or effect.

                                   SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                                           February 14, 2005
                                                       -------------------------
                                                                 Date

                                                        /s/ Howard Kirk Mehaffey
                                                       -------------------------
                                                               Signature

                                                          Howard Kirk Mehaffey
                                                       -------------------------
                                                               Name/Title

                                                          Sole Managing 
                                                          Partner, CAV-RDV, Ltd.

         The original statement shall be signed by each person on whose behalf
the statement is filed or his authorized representative. If the statement is
signed on behalf of a person by his authorized representative other than an
executive officer or general partner of the filing person, evidence of the
representative's authority to sign on behalf of such person shall be filed with
the statement, provided, however, that a power of attorney for this purpose
which is already on file with the Commission may be incorporated by reference.
The name and any title of each person who signs the statement shall be typed or
printed beneath his signature.

NOTE: Schedules filed in paper format shall include a signed original and five
copies of the schedule, including all exhibits. See Section 240.13d-7 for other
parties for whom copies are to be sent.

         ATTENTION: INTENTIONAL MISSTATEMENTS OR OMISSIONS OF FACT CONSTITUTE
FEDERAL CRIMINAL VIOLATIONS (SEE 18 U.S.C. 1001)


                               Page 6 of 6 pages