Document:

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                                                                   Exhibit 10.12

THE WARRANTS AND UNDERLYING SHARES OF COMMON STOCK REPRESENTED BY THIS
CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 (THE
"ACT"), AND ARE "RESTRICTED SECURITIES" AS THAT TERM IS DEFINED IN RULE 144
UNDER THE ACT. THE SECURITIES MAY NOT BE OFFERED FOR SALE, SOLD OR OTHERWISE
TRANSFERRED EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE
ACT, OR PURSUANT TO AN EXEMPTION FROM REGISTRATION UNDER THE ACT, THE
AVAILABILITY OF WHICH IS TO BE ESTABLISHED TO THE SATISFACTION OF THE COMPANY.

                         Warrant Certificate No. DG-___
                           Issue Date: March 31, 2001

                      WARRANT TO PURCHASE _________ SHARES
            VOID AFTER 5:00 P.M., MOUNTAIN TIME, ON DECEMBER 31, 2006

                        NATURAL GAS SERVICES GROUP, INC.
                        WARRANT AGREEMENT AND CERTIFICATE

         This certifies that, for value received, ___________, the registered
holder hereof (the "Warrant Holder"), is entitled to purchase from Natural Gas
Services Group, Inc., a Colorado corporation (the "Company") with its principal
office located in Midland, Texas, at any time commencing on the Issue Date set
forth above, and before 5:00 P.M., Mountain Time, on December 31, 2006 (the
"Termination Date") at the purchase price of $2.50 per share (the "Exercise
Price"), the number of shares of the Company's Common Stock (the "Shares") set
forth above. The number of Shares purchasable upon exercise of this Warrant and
the Exercise Price per Share shall be subject to adjustment from time to time as
set forth in Section 5 below.

Section 1. Sale and Delivery of Warrant. The Warrants represented hereby were
issued as consideration for guaranty of corporate debt in the amount of $_______
by the Warrant Holder.

Section 2. Transfer or Exchange of Warrant.

2.1 The Company shall be entitled to treat the registered owner of any Warrant
(the "Warrant Holder") as the owner in fact thereof for all purposes and shall
not be bound to recognize any equitable or other claim to or interest in such
Warrant on the part of any other person, and shall not be liable for any
registration of transfer of Warrants which are registered or to be registered in
the name of a fiduciary or the nominee of a fiduciary unless made with the
actual knowledge that a fiduciary or nominee is committing a breach of trust in
requesting such registration of transfer, or with such knowledge of such facts
that its participation therein amounts to gross negligence or bad faith.

2.2 This Warrant may not be sold, transferred, assigned or hypothecated except
pursuant to all applicable federal and state securities laws.

2.3 A Warrant shall be transferable only on the books of the Company upon
delivery of this Warrant Certificate duly endorsed by the Warrant Holder or by
his duly authorized attorney or representative, or accompanied by proper
evidence of succession, assignment or authority to transfer.
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Upon any registration of transfer, the Company shall deliver a new Warrant
Certificate to the persons entitled thereto.

Section 3. Term of Warrants; Exercise of Warrants.

3.1 Subject to the terms of this Agreement and Certificate, the Warrant Holder
has the right, which may be exercised commencing immediately and ending at 5:00
p.m. Mountain Time on the Termination Date, to purchase from the Company the
number of Shares which the Warrant Holder may at that time be entitled to
purchase on exercise of this Warrant.

3.2 A Warrant shall be exercised by surrender to the Company, at its principal
office, of this Warrant Agreement and Certificate, together with the form of
election to purchase attached hereto as Exhibit A, duly completed and signed,
and payment to the Company of the Exercise Price (as defined in accordance with
the provisions of Section 4 hereof) for the number of Shares in respect of which
such Warrant is then exercised. Except as provided in Section 3.3, payment of
the aggregate Exercise Price shall be made in cash or certified funds.

3.3 In addition to and without limiting the rights of the Holder under the terms
of this Warrant, the Holder shall have the right (the "Conversion Right") to
convert this Warrant or any portion thereof into Shares as provided in this
Section 3.3 at any time prior to the Termination Date.

         a. Upon exercise of the Conversion Right with respect to a particular
number of Shares (the "Converted Shares"), the Company shall deliver to the
Holder, without payment by the Holder of any Exercise Price or any cash or other
consideration, that number of Shares equal to the quotient obtained by dividing
the Net Value (as hereinafter defined) of the Converted Shares by the fair
market value (as defined in paragraph 3.3(c) below) of a single Share,
determined in each case as of the close of business on the Conversion Date (as
hereinafter defined). The "Net Value" of the Converted Shares shall be
determined by subtracting the aggregate Exercise Price of the Converted Shares
from the aggregate fair market value of the Converted Shares. No fractional
securities shall be issuable upon exercise of the Conversion Right, and if the
number of securities to be issued in accordance with the foregoing formula is
other than a whole number, the Company shall pay to the Holder an amount in cash
equal to the fair market value of the resulting fractional Share.

         b. The Conversion Right may be exercised by the Holder by the surrender
of this Warrant at the principal office of the Company or at the office of the
Company's stock transfer agent, if any, together with a written statement
specifying that the Holder thereby intends to exercise the Conversion Right and
indicating the number of Shares subject to the Warrant which are being
surrendered (referred to in subparagraph 3.3(a) above as the Converted Shares),
in the form attached to and by this reference incorporated in this Warrant as
Exhibit B, in exercise of the Conversion Right. Such conversion shall be
effective upon receipt by the Company of this Warrant together with the
aforesaid written statement, or on such later date as is specified therein (the
"Conversion Date"), but not later than the expiration date of the Warrant.
Certificates for the Converted Shares issuable upon exercise of the Conversion
Right, together with a check in payment of any fractional Warrant Share and, in
the case of a partial exercise a new warrant evidencing the Warrant Shares
remaining

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subject to the Warrant, shall be issued as of the Conversion Date and shall be
delivered to the Holder within twenty-one days following the Conversion Date.

         c. For purposes of this Section 2.3, the "fair market value" of a Share
as of a particular date shall be its "market price," which, for purposes of this
Section 2.3 shall mean, if the Shares are traded on a securities exchange or on
Nasdaq, the closing price of the Shares on such exchange or the last sale price
on Nasdaq, or, if the Shares are otherwise traded in the over-the-counter
market, the average of the closing bid and ask price, in each case averaged over
a period of five consecutive trading days prior to the date as of which "market
price" is being determined. If at any time the Shares are not traded on an
exchange or Nasdaq, or otherwise traded in the over-the-counter market, the
"market price" shall be deemed to be the fair value thereof determined in good
faith by the Board of Directors of the Company as of a date which is within 15
days of the date as of which the determination is to be made.

3.4 Subject to Section 5 hereof, upon surrender of a Warrant Agreement and
Certificate and payment of the Exercise Price as aforesaid, the Company shall
issue and cause to be delivered with all reasonable dispatch to or upon the
written order of the Warrant Holder exercising such Warrant and in such name or
names as such Warrant Holder may designate, certificates for the number of
Shares so purchased upon the exercise of such Warrant. Such certificate or
certificates shall be deemed to have been issued and any person so designated to
be named therein shall be deemed to have become a holder of record of such
Shares as of the date of receipt by the Company of such Warrant Agreement and
Certificate and payment of the Exercise Price. The rights of purchase
represented by the Warrants shall be exercisable, at the election of the Warrant
Holders thereof, either in full or from time to time in part and, in the event
that a Warrant Agreement and Certificate is exercised to purchase less than all
of the Shares purchasable on such exercise at any time prior to the Termination
Date, a new Warrant Agreement and Certificate evidencing the remaining Warrant
or Warrants will be issued.

3.5 The Warrant Holder will pay all documentary stamp taxes, if any,
attributable to the initial issuance of the Shares upon the exercise of
Warrants.

4. REGISTRATION RIGHTS

4.1 The Warrant Holder shall have the following rights with respect to
registration by the Company of the shares of Common Stock issuable upon exercise
of this Warrant. Such shares are referred to hereafter as the "Warrant Shares."

         a. At any time within the period commencing one year from the date
hereof and expiring six years from the date hereof, whenever the Company files a
registration statement under the Securities Act of 1933 which relates to an
initial public offering of the Company's Common Stock, the Company shall offer
to the Warrant Holder the opportunity to register or qualify the Warrant Shares
for public sale, and the Company shall be required to include the Warrant Shares
in the registration statement if the holders of a majority of the Warrant Shares
(calculated as if all placement agent warrants had been exercised) request that
their Warrant Shares be included; provided, however, that if the offering to
which the proposed registration statement relates is an

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underwritten offering and such underwriter objects to the inclusion of the
Warrant Shares in such registration statement, the Company shall be under no
obligation to include any Warrant Shares, except that the Warrant Holder shall
be entitled to have its Warrant Shares included pro rata with all other selling
Warrant Holders. The Company will pay all fees of such registration, other than
underwriters' discounts or commissions relating to Warrant Shares registered on
behalf of the Warrant Holder and fees of separate counsel, if any, engaged by
the Warrant Holder. The Company shall give 20 days' prior written notice to the
Warrant Holder of the Company's intention to file a registration statement under
the Act, which notice shall constitute an offer to the Warrant Holder to have
its Warrant Shares included in such registration statement as long as a majority
of the Warrant Holders so elect, and the Warrant Holder shall notify the Company
in writing within ten days after receipt of such notice if the Warrant Holder
desires to accept such offer. Neither the delivery of such notice nor the
acceptance by the Warrant Holder of such offer (such Warrant Holder a
"Participating Warrant Holder") shall obligate the Company to file such
registration statement and, notwithstanding the actual filing of the
registration statement, the Company may at any time prior to its effectiveness
elect not to pursue the registration without liability to the Warrant Holder.

         b. In the event the underwriter for the Company's initial public
offering of its Common Stock objects to the inclusion of all Warrant Shares held
by Warrant Holders who elected to be included in the registration statement
under the preceding paragraph, then not less than a majority of the Warrant
Holders of those Warrant Shares excluded due to the underwriter's objection may
demand that the Company effect a registration on Form S-3 to include the
previously excluded Warrant Shares. The Company will use commercially reasonable
efforts to effect as soon as practicable the registration under the Act of all
such previously excluded Warrant Shares. This right to demand registration on
Form S-3 is effective only if the Company is eligible to use Form S-3.

         c. The Company's contractual obligation to include the Warrant Shares
on behalf of the Warrant Holder in a registration statement filed on behalf of
the Company shall be subject to the reasonable cooperation of the Warrant Holder
with the Company. The Warrant Shares held by the Warrant Holder may be excluded
from a registration statement at the election of the Company in the event all
information essential for the Company and its counsel to prepare the
registration statement is not furnished by the Warrant Holder, after the Warrant
Holder, upon written request of the Company or its counsel, has been given a
reasonable amount of time (not less than ten business days from the date such
request has been sent to the Warrant Holder) to transmit the requested
information to the Company and/or its counsel.

4.2 A Participating Warrant Holder will provide the Company such information
relating to the Participating Warrant Holder and its plan of distribution as may
be necessary for the completion of the registration statement.

4.3 In the event of any registration under the Act of any of the Warrant Shares
pursuant to this Agreement, the Company will use its best efforts to obtain blue
sky qualification of the Warrant

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Shares in such states as the Company may agree upon reasonable request of the
Participating Warrant Holder.

4.4 In the event of any registration under the Act of any of the Warrant Shares
pursuant to this Agreement, the Participating Warrant Holder will be responsible
for ensuring that the Warrant Shares are sold in strict compliance with the
registration statement (including, without limitation, the plan of distribution
to be included therein) and all other applicable federal and state securities
laws and regulations.

4.5 In the event of any registration under the Act of any of the Warrant Shares
pursuant to this Agreement, the Company will agree to indemnify and hold
harmless each Participating Warrant Holder and each underwriter, and each other
affiliate of a Participating Warrant Holder or such underwriter within the
meaning of the Act against any losses, claims, damages or liabilities, joint or
several, to which any Participating Warrant Holder or such underwriter or such
controlling person may become subject under the Act or otherwise, insofar as
such losses, claims, damages or liabilities (or actions in respect thereof)
arise out of or are based upon any untrue statement or alleged untrue statement
of any material fact contained, on the effective date thereof, in any such
registration statement, any preliminary prospectus or final prospectus contained
therein or any amendment thereof or supplement thereto, or any document incident
to registration or qualification of the Warrant Shares covered thereby under
state securities or blue sky laws, or arise out of or are based upon the
omission or alleged omission to state therein a material fact required to be
stated therein, or any violation by the Company of the Act or state securities
or blue sky laws applicable to the Company and relating to any action or
inaction required by the Company in connection with such registration or
qualification under such state securities or blue sky laws; provided, however
that the Company will not be liable in any such case to any indemnified person
to the extent that any such loss, claim, damage or liability arises out of or is
based upon an untrue statement or alleged untrue statement or omission or
alleged omission made in such registration statement, said preliminary
prospectus or said prospectus or said amendment or supplement, or any document
incident to registration or qualification under state securities or blue sky
laws, in reliance upon and in conformity with any information furnished in
writing to the Company or its counsel by such indemnified person specifically
for use in the preparation thereof or if such loss, claim, damage, liability or
action arose out of the violation of any duty to which the Participating Warrant
Holder may be subject, including the obligation to deliver a copy of any
prospectus, supplement or amendment to a purchaser of the Warrant Shares and
such prospectus, supplement or amendment was made available to the Participating
Warrant Holder by the Company.

4.6 In the event of any registration of the Warrant Shares under the Act
pursuant to this Agreement, each Participating Warrant Holder will agree to
indemnify and hold harmless the Company and each affiliate and controlling
person, as defined by the Act, of the Company, each officer or employee of the
Company who signs the registration statement, each director of the Company, any
agent of the Company and each underwriter, and any and all affiliates and
controlling persons, as defined by the Act, of such persons against any and all
such losses, claims, damages or liabilities as the Participating Warrant Holders
and others are indemnified against by the Company and will reimburse the Company
and each of the foregoing persons for any losses, claims, damages or liabilities
(or actions in respect thereof) and for any legal or any other expenses incurred
by each

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such person, if the statement or omission in respect of which such loss, claim,
damage or liability is asserted was made in reliance upon and in conformity with
information furnished to the Company in writing by such Participating Warrant
Holder or on its behalf specifically for use in connection with the preparation
of such registration statement or prospectus.

Section 5. Adjustment of Exercise Price and Shares.

5.1 If the Company shall at any time subdivide its outstanding Common Stock by
recapitalization, reclassification or split-up thereof, the number of Shares of
Common Stock subject to this Warrant immediately prior to such subdivision shall
be proportionately increased, and if the Company shall at any time combine the
outstanding Common Stock by recapitalization, reclassification or combination
thereof, the number of Shares of Common Stock subject to this Warrant
immediately prior to such combination shall be proportionately decreased. Any
corresponding adjustment to the Exercise Price shall become effective at the
close of business on the record date for such subdivision or combination.

5.2 In the event of a dividend (other than in shares of Common Stock of the
Company), the proposed dissolution or liquidation of the Company, or any
corporate separation or division, including, but not limited to, a split-up,
split-off or spin-off, or a merger or consolidation of the Company with another
Company, or the sale of all or substantially all of the assets of the Company,
the Board may provide that each Warrantholder will have the right to exercise
this Warrant (at its then current Exercise Price) solely for the kind and amount
of shares of stock and other securities, property, cash or any combination
thereof receivable upon such dissolution, liquidation, corporate separation or
division, or merger or consolidation by a holder of the number of shares of
Common Stock for which this Warrant might have been exercised immediately prior
to such dissolution, liquidation, corporate separation or division, or merger or
consolidation; or, in the alternative, the Board may provide that this Warrant
will terminate as of a date fixed by the Board; provided, however that not less
than 30 days' written notice of the date so fixed must be given to the
Warrantholder, who will have the right, during the period of 30 days preceding
such termination, to exercise this Warrant as to all or any part of the shares
of Common Stock covered by this Warrant.

5.3 The preceding paragraph will not apply to a merger or consolidation in which
the Company is the surviving Company and shares of Common Stock are not
converted into or exchanged for stock, securities of any other Company, cash or
any other thing of value. Notwithstanding the preceding sentence, in case of any
consolidation or merger of another Company into the Company in which the Company
is the surviving Company and in which there is a reclassification or change
(including a change to the right to receive cash or other property) of the
shares of Common Stock (excluding a change in par value, or from no par value to
par value, or any change as a result of a subdivision or combination, but
including any change in such shares into two or more classes or series of
shares), the Board may provide that the holder of this Warrant will have the
right to exercise this Warrant solely for the kind and amount of shares of stock
and other securities (including those of any new direct or indirect parent of
the Company), property, cash or any combination thereof receivable upon such
reclassification, change, consolidation or merger by the holder of the number of
shares of Common Stock for which this Warrant might have been exercised.

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5.4 In the event of a change in the Common Stock of the Company as presently
constituted into the same number of shares with a different par value, the
shares resulting from any such change will be deemed to be the Common Stock of
the Company within the meaning of this agreement.

5.5 The Company agrees that without the Warrant Holder's consent or absent
consent, without a reasonable adjustment to the Exercise Price of this Warrant,
no shares of Common Stock, and no securities convertible into shares of Common
Stock, will be issued at a price per share (or a conversion price, if
applicable) less than the fair market value of the Company's Common Stock on the
date of issuance; provided, however that this paragraph will not apply to: (i)
options granted under the Company's 1998 Stock Option Plan; or (ii) securities
issued in connection with any merger or acquisition.

5.6 To the extent that the foregoing adjustments relate to stock or securities
of the Company, such adjustments will be made in good faith by the Board.

5.7 Except as expressly provided in this Warrant, the Warrantholder will have no
rights by reason of any subdivision or consolidation of shares of stock of any
class, or the payment of any stock dividend or any other increase or decrease in
the number of shares of stock of any class, or by reason of any dissolution,
liquidation, merger, or consolidation or spin-off of assets or stock of another
Company; and any issue by the Company of shares of stock of any class, or
securities convertible into shares of stock of any class, will not affect, and
no adjustment will be made with respect to, the number or price of shares of
Common Stock subject to this Warrant. The grant of this Warrant will not affect
in any way the right or power of the Company to make adjustments,
reclassifications, reorganizations or changes of its capital or business
structures, or to merge or consolidate, or to dissolve, liquidate, or sell or
transfer all or any part of its business or assets.

Section 6. Mutilated or Missing Warrant Certificates. In case any Warrant
Certificate shall be mutilated, lost, stolen or destroyed, the Company shall, at
the request of the holder of such Certificate, issue and deliver, in exchange
and substitution for and upon cancellation of the mutilated Certificate, or in
lieu of and substitution for the Certificate, lost, stolen or destroyed, a new
Warrant Certificate of like tenor and representing an equivalent right or
interest; but only upon receipt of evidence satisfactory to the Company of such
loss, theft or destruction of such Warrant Certificate and indemnity, if
requested, also satisfactory to the Company. An applicant for such a substitute
Warrant Certificate shall also comply with such other reasonable regulations and
pay such other reasonable charges as the Company may prescribe.

Section 7. Reservation of Shares of Common Stock. There has been reserved, and
the Company shall at all times keep reserved so long as any of the Warrants
remain outstanding, out of its authorized Common Stock a number of shares of
Common Stock sufficient to provide for the exercise of the rights of purchase
represented by the outstanding Warrants and the underlying securities.

Section 8. No Fractional Shares. The Company shall not be required to issue
fractional shares or scrip representing fractional shares upon the exercise of
the Warrants. As to any final fraction of a Share which the Warrant Holder would
otherwise be entitled to purchase upon such exercise, the

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Company shall pay a cash adjustment in respect of such final fraction in an
amount equal to the same fraction of the market price of a share of Common Stock
on the business day preceding the day of exercise.

Section 9. Transfer and Exercise to Comply With the Securities Act of 1933.

9.1 Neither the Warrants nor the Warrant Shares may be sold, transferred or
otherwise disposed of except to a person, who, in the opinion of counsel for the
Company, is a person to whom such securities may legally be transferred pursuant
to the provisions of this Agreement without registration, and without the
delivery of a current prospectus, under the Act with respect thereto.

9.2 Unless the Company has on file with the Securities and Exchange Commission a
current registration statement to permit the Company to issue registered shares
upon exercise of the Warrants, the Warrants may not be exercised except in a
transaction exempt from registration under the Act.

9.3 The Company shall cause the following legend to be set forth on each Warrant
Certificate and certificates representing the Warrant Shares, unless counsel for
the Company is of the opinion as to any such Certificates that such legend is
unnecessary:

                  The securities represented by this certificate may not be
                  offered for sale, sold or otherwise transferred except
                  pursuant to an effective registration statement made under the
                  Securities Act of 1933 (the "Act"), or pursuant to an
                  exemption from registration under the Act the availability of
                  which is to be established to the satisfaction of the Company.

Section 10. Notices. Any notice pursuant to this Agreement by the Company or by
the Warrant Holders shall be in writing and shall be deemed to have been duly
given if delivered or mailed certified mail, return receipt requested, (a) if to
the Company, to Natural Gas Services Group, Inc., 2911 So. County Road 1260,
Midland, TX 79706, attn: President; and (b) if to the Warrant Holder, to the
address set forth above. Each party hereto may from time to time change the
address to which notices to it are to be delivered or mailed hereunder by notice
in accordance herewith to the other party.

Section 11. Successors. All the covenants and provisions of this Agreement by or
for the benefit of the Company or the Warrant Holders shall bind and inure to
the benefit of their respective successors and assigns hereunder.

Section 12. Applicable Law. This Warrant Agreement and Certificate and any
replacement Certificate issued hereunder shall be deemed to be a contract made
under the laws of the State of Colorado and for all purposes shall be construed
in accordance with the laws of said State.

Section 13. Benefits of This Agreement. Nothing in this Agreement shall be
construed to give to any person or Company other than the Company and the
Warrant Holders any legal or equitable right, remedy or claim under this
Agreement and this Agreement shall be for the sole and exclusive benefit of the
Company and the Warrant Holders.

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DATED: March 31, 2001    NATURAL GAS SERVICES GROUP, INC.

                                      By:
                                           -------------------------------------
                                           Wallace Sparkman, President

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                                                                       EXHIBIT A
                                  PURCHASE FORM

                                                     DATED _______________, ____

         THE UNDERSIGNED HEREBY IRREVOCABLY ELECTS TO EXERCISE THE WARRANT
REPRESENTED BY THIS WARRANT CERTIFICATE TO THE EXTENT OF PURCHASING __________
SHARES OF NATURAL GAS SERVICES GROUP, INC. AND HEREBY MAKES PAYMENT OF $2.50 PER
SHARE IN PAYMENT OF THE EXERCISE PRICE THEREOF.

                     INSTRUCTIONS FOR REGISTRATION OF STOCK

NAME:

-------------------------------------------------------------------------------
                     (PLEASE TYPE OR PRINT IN BLOCK LETTERS)
ADDRESS:

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

SIGNATURE
         ------------------------------------------------------

DATED:
       ------------------, ------

                                 ASSIGNMENT FORM

     FOR VALUE RECEIVED, __________________________, HEREBY SELLS, ASSIGNS
     AND TRANSFERS UNTO

NAME:

-------------------------------------------------------------------------------
                     (PLEASE TYPE OR PRINT IN BLOCK LETTERS)

ADDRESS:

-------------------------------------------------------------------------------
THE RIGHT TO PURCHASE SHARES OF NATURAL GAS SERVICES GROUP, INC. REPRESENTED BY
THIS WARRANT CERTIFICATE TO THE EXTENT OF _________ SHARES AS TO WHICH SUCH
RIGHT IS EXERCISABLE AND DOES HEREBY IRREVOCABLY CONSTITUTE AND APPOINT NATURAL
GAS SERVICES GROUP, INC. TO TRANSFER THE SAME ON THE BOOKS OF THE COMPANY WITH
FULL POWER OF SUBSTITUTION IN THE PREMISES.
------------------------------------------------------
SIGNATURE
         ------------------------------------------------------

DATED:
       ------------------, ------

                                    NOTICE: THE SIGNATURE OF THIS ASSIGNMENT
                                    MUST CORRESPOND WITH THE NAME AS IT APPEARS
                                    UPON THE FACE OF THIS WARRANT CERTIFICATE IN
                                    EVERY PARTICULAR, WITHOUT ALTERATION OR
                                    ENLARGEMENT OR ANY CHANGE WHATEVER.
<PAGE>
                                                                       EXHIBIT B

                        WARRANT CONVERSION EXERCISE FORM

TO: NATURAL GAS SERVICES GROUP, INC.

         Pursuant to Section 2.3 of the Warrant Certificate from Natural Gas
Services Group, Inc. (the "Company") to the undersigned Holder, the Holder
hereby irrevocably elects to convert Warrants with respect to Shares of the
Company into ___________ Shares of the Company.

A conversion calculation is attached hereto as Exhibit B-1.

         The undersigned requests that certificates for such Shares be issued as
follows:

     Name:
                  ------------------------------------------
     Address:
                  ------------------------------------------

     Deliver to:
                  ------------------------------------------

and that a new Warrant Certificate for the balance remaining of the Warrants, if
any, subject to the Warrant be registered in the name of, and delivered to, the
undersigned at the address stated above.

     Dated:
                  --------------------------

                                                        ------------------------
                                                        [NAME OF WARRANT HOLDER]
<PAGE>
                                                                     EXHIBIT B-1

                        CALCULATION OF WARRANT CONVERSION

Shares to be Delivered by Company     =      Net Value
                                             _________
                                                fmv

                         fmv          =      $____________

                         Net Value    =      aggregate fmv of Converted Shares -
                                             aggregate Exercise Price of
                                             Converted Shares

                                      =      $____________ - $____________

                                      =      $____________

Shares to be Delivered by Company     =      _____________

                Fractional Shares     =      ____________<PAGE>
                                                                   Exhibit 10.13

THE WARRANTS AND UNDERLYING SHARES OF COMMON STOCK REPRESENTED BY THIS
CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 (THE
"ACT"), AND ARE "RESTRICTED SECURITIES" AS THAT TERM IS DEFINED IN RULE 144
UNDER THE ACT. THE SECURITIES MAY NOT BE OFFERED FOR SALE, SOLD OR OTHERWISE
TRANSFERRED EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE
ACT, OR PURSUANT TO AN EXEMPTION FROM REGISTRATION UNDER THE ACT, THE
AVAILABILITY OF WHICH IS TO BE ESTABLISHED TO THE SATISFACTION OF THE COMPANY.

                                                  Warrant Certificate No. DG-___
                                                      Issue Date: April 24, 2002

                       WARRANT TO PURCHASE ________ SHARES
             VOID AFTER 5:00 P.M., MOUNTAIN TIME, ON APRIL 23, 2007

                        NATURAL GAS SERVICES GROUP, INC.
                        WARRANT AGREEMENT AND CERTIFICATE

         This certifies that, for value received, _____________, the registered
holder hereof (the "Warrant Holder"), is entitled to purchase from Natural Gas
Services Group, Inc., a Colorado corporation (the "Company") with its principal
office located in Midland, Texas, at any time commencing on the Issue Date set
forth above, and before 5:00 P.M., Mountain Time, on April 23, 2007 (the
"Termination Date") at the purchase price of $3.25 per share (the "Exercise
Price"), the number of shares of the Company's Common Stock (the "Shares") set
forth above. The number of Shares purchasable upon exercise of this Warrant and
the Exercise Price per Share shall be subject to adjustment from time to time as
set forth in Section 5 below.

Section 1. Sale and Delivery of Warrant. The Warrants represented hereby were
issued as consideration for guaranty of additional corporate debt in the amount
of $___________ by the Warrant Holder.

Section 2. Transfer or Exchange of Warrant.

2.1 The Company shall be entitled to treat the registered owner of any Warrant
(the "Warrant Holder") as the owner in fact thereof for all purposes and shall
not be bound to recognize any equitable or other claim to or interest in such
Warrant on the part of any other person, and shall not be liable for any
registration of transfer of Warrants which are registered or to be registered in
the name of a fiduciary or the nominee of a fiduciary unless made with the
actual knowledge that a fiduciary or nominee is committing a breach of trust in
requesting such registration of transfer, or with such knowledge of such facts
that its participation therein amounts to gross negligence or bad faith.

2.2 This Warrant may not be sold, transferred, assigned or hypothecated except
pursuant to all applicable federal and state securities laws.

2.3 A Warrant shall be transferable only on the books of the Company upon
delivery of this Warrant Certificate duly endorsed by the Warrant Holder or by
his duly authorized attorney or representative, or accompanied by proper
evidence of succession, assignment or authority to
<PAGE>
transfer. Upon any registration of transfer, the Company shall deliver a new
Warrant Certificate to the persons entitled thereto.

Section 3. Term of Warrants; Exercise of Warrants.

3.1 Subject to the terms of this Agreement and Certificate, the Warrant Holder
has the right, which may be exercised commencing immediately and ending at 5:00
p.m. Mountain Time on the Termination Date, to purchase from the Company the
number of Shares which the Warrant Holder may at that time be entitled to
purchase on exercise of this Warrant.

3.2 A Warrant shall be exercised by surrender to the Company, at its principal
office, of this Warrant Agreement and Certificate, together with the form of
election to purchase attached hereto as Exhibit A, duly completed and signed,
and payment to the Company of the Exercise Price (as defined in accordance with
the provisions of Section 4 hereof) for the number of Shares in respect of which
such Warrant is then exercised. Except as provided in Section 3.3, payment of
the aggregate Exercise Price shall be made in cash or certified funds.

3.3 In addition to and without limiting the rights of the Holder under the terms
of this Warrant, the Holder shall have the right (the "Conversion Right") to
convert this Warrant or any portion thereof into Shares as provided in this
Section 3.3 at any time prior to the Termination Date.

         a. Upon exercise of the Conversion Right with respect to a particular
number of Shares (the "Converted Shares"), the Company shall deliver to the
Holder, without payment by the Holder of any Exercise Price or any cash or other
consideration, that number of Shares equal to the quotient obtained by dividing
the Net Value (as hereinafter defined) of the Converted Shares by the fair
market value (as defined in paragraph 3.3(c) below) of a single Share,
determined in each case as of the close of business on the Conversion Date (as
hereinafter defined). The "Net Value" of the Converted Shares shall be
determined by subtracting the aggregate Exercise Price of the Converted Shares
from the aggregate fair market value of the Converted Shares. No fractional
securities shall be issuable upon exercise of the Conversion Right, and if the
number of securities to be issued in accordance with the foregoing formula is
other than a whole number, the Company shall pay to the Holder an amount in cash
equal to the fair market value of the resulting fractional Share.

         b. The Conversion Right may be exercised by the Holder by the surrender
of this Warrant at the principal office of the Company or at the office of the
Company's stock transfer agent, if any, together with a written statement
specifying that the Holder thereby intends to exercise the Conversion Right and
indicating the number of Shares subject to the Warrant which are being
surrendered (referred to in subparagraph 3.3(a) above as the Converted Shares),
in the form attached to and by this reference incorporated in this Warrant as
Exhibit B, in exercise of the Conversion Right. Such conversion shall be
effective upon receipt by the Company of this Warrant together with the
aforesaid written statement, or on such later date as is specified therein (the
"Conversion Date"), but not later than the expiration date of the Warrant.
Certificates for the Converted Shares issuable upon exercise of the Conversion
Right, together with a check in payment of any fractional Warrant Share and, in
the case of a partial exercise a

                                       2
<PAGE>
new warrant evidencing the Warrant Shares remaining subject to the Warrant,
shall be issued as of the Conversion Date and shall be delivered to the Holder
within twenty-one days following the Conversion Date.

         c. For purposes of this Section 2.3, the "fair market value" of a Share
as of a particular date shall be its "market price," which, for purposes of this
Section 2.3 shall mean, if the Shares are traded on a securities exchange or on
Nasdaq, the closing price of the Shares on such exchange or the last sale price
on Nasdaq, or, if the Shares are otherwise traded in the over-the-counter
market, the average of the closing bid and ask price, in each case averaged over
a period of five consecutive trading days prior to the date as of which "market
price" is being determined. If at any time the Shares are not traded on an
exchange or Nasdaq, or otherwise traded in the over-the-counter market, the
"market price" shall be deemed to be the fair value thereof determined in good
faith by the Board of Directors of the Company as of a date which is within 15
days of the date as of which the determination is to be made.

3.4 Subject to Section 5 hereof, upon surrender of a Warrant Agreement and
Certificate and payment of the Exercise Price as aforesaid, the Company shall
issue and cause to be delivered with all reasonable dispatch to or upon the
written order of the Warrant Holder exercising such Warrant and in such name or
names as such Warrant Holder may designate, certificates for the number of
Shares so purchased upon the exercise of such Warrant. Such certificate or
certificates shall be deemed to have been issued and any person so designated to
be named therein shall be deemed to have become a holder of record of such
Shares as of the date of receipt by the Company of such Warrant Agreement and
Certificate and payment of the Exercise Price. The rights of purchase
represented by the Warrants shall be exercisable, at the election of the Warrant
Holders thereof, either in full or from time to time in part and, in the event
that a Warrant Agreement and Certificate is exercised to purchase less than all
of the Shares purchasable on such exercise at any time prior to the Termination
Date, a new Warrant Agreement and Certificate evidencing the remaining Warrant
or Warrants will be issued.

3.5 The Warrant Holder will pay all documentary stamp taxes, if any,
attributable to the initial issuance of the Shares upon the exercise of
Warrants.

4. REGISTRATION RIGHTS

4.1 The Warrant Holder shall have the following rights with respect to
registration by the Company of the shares of Common Stock issuable upon exercise
of this Warrant. Such shares are referred to hereafter as the "Warrant Shares."

         a. At any time within the period commencing one year from the date
hereof and expiring six years from the date hereof, whenever the Company files a
registration statement under the Securities Act of 1933 which relates to an
initial public offering of the Company's Common Stock, the Company shall offer
to the Warrant Holder the opportunity to register or qualify the Warrant Shares
for public sale, and the Company shall be required to include the Warrant Shares
in the registration statement if the holders of a majority of the Warrant Shares
(calculated as if all placement agent warrants had been exercised) request that
their Warrant Shares be included; provided, however, that if the offering to
which the proposed registration

                                       3
<PAGE>
statement relates is an underwritten offering and such underwriter objects to
the inclusion of the Warrant Shares in such registration statement, the Company
shall be under no obligation to include any Warrant Shares, except that the
Warrant Holder shall be entitled to have its Warrant Shares included pro rata
with all other selling Warrant Holders. The Company will pay all fees of such
registration, other than underwriters' discounts or commissions relating to
Warrant Shares registered on behalf of the Warrant Holder and fees of separate
counsel, if any, engaged by the Warrant Holder. The Company shall give 20 days'
prior written notice to the Warrant Holder of the Company's intention to file a
registration statement under the Act, which notice shall constitute an offer to
the Warrant Holder to have its Warrant Shares included in such registration
statement as long as a majority of the Warrant Holders so elect, and the Warrant
Holder shall notify the Company in writing within ten days after receipt of such
notice if the Warrant Holder desires to accept such offer. Neither the delivery
of such notice nor the acceptance by the Warrant Holder of such offer such
Warrant Holder a "Participating Warrant Holder") shall obligate the Company to
file such registration statement and, notwithstanding the actual filing of the
registration statement, the Company may at any time prior to its effectiveness
elect not to pursue the registration without liability to the Warrant Holder.

         b. In the event the underwriter for the Company's initial public
offering of its Common Stock objects to the inclusion of all Warrant Shares held
by Warrant Holders who elected to be included in the registration statement
under the preceding paragraph, then not less than a majority of the Warrant
Holders of those Warrant Shares excluded due to the underwriter's objection may
demand that the Company effect a registration on Form S-3 to include the
previously excluded Warrant Shares. The Company will use commercially reasonable
efforts to effect as soon as practicable the registration under the Act of all
such previously excluded Warrant Shares. This right to demand registration on
Form S-3 is effective only if the Company is eligible to use Form S-3.

         c. The Company's contractual obligation to include the Warrant Shares
on behalf of the Warrant Holder in a registration statement filed on behalf of
the Company shall be subject to the reasonable cooperation of the Warrant Holder
with the Company. The Warrant Shares held by the Warrant Holder may be excluded
from a registration statement at the election of the Company in the event all
information essential for the Company and its counsel to prepare the
registration statement is not furnished by the Warrant Holder, after the Warrant
Holder, upon written request of the Company or its counsel, has been given a
reasonable amount of time (not less than ten business days from the date such
request has been sent to the Warrant Holder) to transmit the requested
information to the Company and/or its counsel.

4.2 A Participating Warrant Holder will provide the Company such information
relating to the Participating Warrant Holder and its plan of distribution as may
be necessary for the completion of the registration statement.

4.3 In the event of any registration under the Act of any of the Warrant Shares
pursuant to this Agreement, the Company will use its best efforts to obtain blue
sky qualification of the Warrant

                                       4
<PAGE>
Shares in such states as the Company may agree upon reasonable request of the
Participating Warrant Holder.

4.4 In the event of any registration under the Act of any of the Warrant Shares
pursuant to this Agreement, the Participating Warrant Holder will be responsible
for ensuring that the Warrant Shares are sold in strict compliance with the
registration statement (including, without limitation, the plan of distribution
to be included therein) and all other applicable federal and state securities
laws and regulations.

4.5 In the event of any registration under the Act of any of the Warrant Shares
pursuant to this Agreement, the Company will agree to indemnify and hold
harmless each Participating Warrant Holder and each underwriter, and each other
affiliate of a Participating Warrant Holder or such underwriter within the
meaning of the Act against any losses, claims, damages or liabilities, joint or
several, to which any Participating Warrant Holder or such underwriter or such
controlling person may become subject under the Act or otherwise, insofar as
such losses, claims, damages or liabilities (or actions in respect thereof)
arise out of or are based upon any untrue statement or alleged untrue statement
of any material fact contained, on the effective date thereof, in any such
registration statement, any preliminary prospectus or final prospectus contained
therein or any amendment thereof or supplement thereto, or any document incident
to registration or qualification of the Warrant Shares covered thereby under
state securities or blue sky laws, or arise out of or are based upon the
omission or alleged omission to state therein a material fact required to be
stated therein, or any violation by the Company of the Act or state securities
or blue sky laws applicable to the Company and relating to any action or
inaction required by the Company in connection with such registration or
qualification under such state securities or blue sky laws; provided, however
that the Company will not be liable in any such case to any indemnified person
to the extent that any such loss, claim, damage or liability arises out of or is
based upon an untrue statement or alleged untrue statement or omission or
alleged omission made in such registration statement, said preliminary
prospectus or said prospectus or said amendment or supplement, or any document
incident to registration or qualification under state securities or blue sky
laws, in reliance upon and in conformity with any information furnished in
writing to the Company or its counsel by such indemnified person specifically
for use in the preparation thereof or if such loss, claim, damage, liability or
action arose out of the violation of any duty to which the Participating Warrant
Holder may be subject, including the obligation to deliver a copy of any
prospectus, supplement or amendment to a purchaser of the Warrant Shares and
such prospectus, supplement or amendment was made available to the Participating
Warrant Holder by the Company.

4.6 In the event of any registration of the Warrant Shares under the Act
pursuant to this Agreement, each Participating Warrant Holder will agree to
indemnify and hold harmless the Company and each affiliate and controlling
person, as defined by the Act, of the Company, each officer or employee of the
Company who signs the registration statement, each director of the Company, any
agent of the Company and each underwriter, and any and all affiliates and
controlling persons, as defined by the Act, of such persons against any and all
such losses, claims, damages or liabilities as the Participating Warrant Holders
and others are indemnified against by the Company and will reimburse the Company
and each of the foregoing persons for any losses, claims, damages or liabilities
(or actions in respect thereof) and for any legal or any

                                       5
<PAGE>
other expenses incurred by each such person, if the statement or omission in
respect of which such loss, claim, damage or liability is asserted was made in
reliance upon and in conformity with information furnished to the Company in
writing by such Participating Warrant Holder or on its behalf specifically for
use in connection with the preparation of such registration statement or
prospectus.

Section 5. Adjustment of Exercise Price and Shares.

5.1 If the Company shall at any time subdivide its outstanding Common Stock by
recapitalization, reclassification or split-up thereof, the number of Shares of
Common Stock subject to this Warrant immediately prior to such subdivision shall
be proportionately increased, and if the Company shall at any time combine the
outstanding Common Stock by recapitalization, reclassification or combination
thereof, the number of Shares of Common Stock subject to this Warrant
immediately prior to such combination shall be proportionately decreased. Any
corresponding adjustment to the Exercise Price shall become effective at the
close of business on the record date for such subdivision or combination.

5.2 In the event of a dividend (other than in shares of Common Stock of the
Company), the proposed dissolution or liquidation of the Company, or any
corporate separation or division, including, but not limited to, a split-up,
split-off or spin-off, or a merger or consolidation of the Company with another
Company, or the sale of all or substantially all of the assets of the Company,
the Board may provide that each Warrantholder will have the right to exercise
this Warrant (at its then current Exercise Price) solely for the kind and amount
of shares of stock and other securities, property, cash or any combination
thereof receivable upon such dissolution, liquidation, corporate separation or
division, or merger or consolidation by a holder of the number of shares of
Common Stock for which this Warrant might have been exercised immediately prior
to such dissolution, liquidation, corporate separation or division, or merger or
consolidation; or, in the alternative, the Board may provide that this Warrant
will terminate as of a date fixed by the Board; provided, however that not less
than 30 days' written notice of the date so fixed must be given to the
Warrantholder, who will have the right, during the period of 30 days preceding
such termination, to exercise this Warrant as to all or any part of the shares
of Common Stock covered by this Warrant.

5.3 The preceding paragraph will not apply to a merger or consolidation in which
the Company is the surviving Company and shares of Common Stock are not
converted into or exchanged for stock, securities of any other Company, cash or
any other thing of value. Notwithstanding the preceding sentence, in case of any
consolidation or merger of another Company into the Company in which the Company
is the surviving Company and in which there is a reclassification or change
(including a change to the right to receive cash or other property) of the
shares of Common Stock (excluding a change in par value, or from no par value to
par value, or any change as a result of a subdivision or combination, but
including any change in such shares into two or more classes or series of
shares), the Board may provide that the holder of this Warrant will have the
right to exercise this Warrant solely for the kind and amount of shares of stock
and other securities (including those of any new direct or indirect parent of
the Company), property, cash or any combination thereof receivable upon such
reclassification, change, consolidation or merger by the holder of the number of
shares of Common Stock for which this Warrant might have been exercised.

                                       6
<PAGE>
5.4 In the event of a change in the Common Stock of the Company as presently
constituted into the same number of shares with a different par value, the
shares resulting from any such change will be deemed to be the Common Stock of
the Company within the meaning of this agreement.

5.5 The Company agrees that without the Warrant Holder's consent or absent
consent, without a reasonable adjustment to the Exercise Price of this Warrant,
no shares of Common Stock, and no securities convertible into shares of Common
Stock, will be issued at a price per share (or a conversion price, if
applicable) less than the fair market value of the Company's Common Stock on the
date of issuance; provided, however that this paragraph will not apply to: (i)
options granted under the Company's 1998 Stock Option Plan; or (ii) securities
issued in connection with any merger or acquisition.

5.6 To the extent that the foregoing adjustments relate to stock or securities
of the Company, such adjustments will be made in good faith by the Board.

5.7 Except as expressly provided in this Warrant, the Warrantholder will have no
rights by reason of any subdivision or consolidation of shares of stock of any
class, or the payment of any stock dividend or any other increase or decrease in
the number of shares of stock of any class, or by reason of any dissolution,
liquidation, merger, or consolidation or spin-off of assets or stock of another
Company; and any issue by the Company of shares of stock of any class, or
securities convertible into shares of stock of any class, will not affect, and
no adjustment will be made with respect to, the number or price of shares of
Common Stock subject to this Warrant. The grant of this Warrant will not affect
in any way the right or power of the Company to make adjustments,
reclassifications, reorganizations or changes of its capital or business
structures, or to merge or consolidate, or to dissolve, liquidate, or sell or
transfer all or any part of its business or assets.

Section 6. Mutilated or Missing Warrant Certificates. In case any Warrant
Certificate shall be mutilated, lost, stolen or destroyed, the Company shall, at
the request of the holder of such Certificate, issue and deliver, in exchange
and substitution for and upon cancellation of the mutilated Certificate, or in
lieu of and substitution for the Certificate, lost, stolen or destroyed, a new
Warrant Certificate of like tenor and representing an equivalent right or
interest; but only upon receipt of evidence satisfactory to the Company of such
loss, theft or destruction of such Warrant Certificate and indemnity, if
requested, also satisfactory to the Company. An applicant for such a substitute
Warrant Certificate shall also comply with such other reasonable regulations and
pay such other reasonable charges as the Company may prescribe.

Section 7. Reservation of Shares of Common Stock. There has been reserved, and
the Company shall at all times keep reserved so long as any of the Warrants
remain outstanding, out of its authorized Common Stock a number of shares of
Common Stock sufficient to provide for the exercise of the rights of purchase
represented by the outstanding Warrants and the underlying securities.

Section 8. No Fractional Shares. The Company shall not be required to issue
fractional shares or scrip representing fractional shares upon the exercise of
the Warrants. As to any final

                                       7
<PAGE>
fraction of a Share which the Warrant Holder would otherwise be entitled to
purchase upon such exercise, the Company shall pay a cash adjustment in respect
of such final fraction in an amount equal to the same fraction of the market
price of a share of Common Stock on the business day preceding the day of
exercise.

Section 9. Transfer and Exercise to Comply With the Securities Act of 1933.

9.1 Neither the Warrants nor the Warrant Shares may be sold, transferred or
otherwise disposed of except to a person, who, in the opinion of counsel for the
Company, is a person to whom such securities may legally be transferred pursuant
to the provisions of this Agreement without registration, and without the
delivery of a current prospectus, under the Act with respect thereto.

9.2 Unless the Company has on file with the Securities and Exchange Commission a
current registration statement to permit the Company to issue registered shares
upon exercise of the Warrants, the Warrants may not be exercised except in a
transaction exempt from registration under the Act.

9.3 The Company shall cause the following legend to be set forth on each Warrant
Certificate and certificates representing the Warrant Shares, unless counsel for
the Company is of the opinion as to any such Certificates that such legend is
unnecessary:

                  The securities represented by this certificate may not be
                  offered for sale, sold or otherwise transferred except
                  pursuant to an effective registration statement made under the
                  Securities Act of 1933 (the "Act"), or pursuant to an
                  exemption from registration under the Act the availability of
                  which is to be established to the satisfaction of the Company.

Section 10. Notices. Any notice pursuant to this Agreement by the Company or by
the Warrant Holders shall be in writing and shall be deemed to have been duly
given if delivered or mailed certified mail, return receipt requested, (a) if to
the Company, to Natural Gas Services Group, Inc., 2911 So. County Road 1260,
Midland, TX 79706, attn: President; and (b) if to the Warrant Holder, to the
address set forth above. Each party hereto may from time to time change the
address to which notices to it are to be delivered or mailed hereunder by notice
in accordance herewith to the other party.

Section 11. Successors. All the covenants and provisions of this Agreement by or
for the benefit of the Company or the Warrant Holders shall bind and inure to
the benefit of their respective successors and assigns hereunder.

Section 12. Applicable Law. This Warrant Agreement and Certificate and any
replacement Certificate issued hereunder shall be deemed to be a contract made
under the laws of the State of Colorado and for all purposes shall be construed
in accordance with the laws of said State.

Section 13. Benefits of This Agreement. Nothing in this Agreement shall be
construed to give to any person or Company other than the Company and the
Warrant Holders any legal or

                                       8
<PAGE>
equitable right, remedy or claim under this Agreement and this Agreement shall
be for the sole and exclusive benefit of the Company and the Warrant Holders.

DATED: April 24, 2002              NATURAL GAS SERVICES GROUP, INC.

                                   By:
                                      ------------------------------------------
                                      Wayne Vinson, President

                                       9
<PAGE>
                                                                       EXHIBIT A
                                  PURCHASE FORM

                                                     DATED _______________, ____

         THE UNDERSIGNED HEREBY IRREVOCABLY ELECTS TO EXERCISE THE WARRANT
REPRESENTED BY THIS WARRANT CERTIFICATE TO THE EXTENT OF PURCHASING __________
SHARES OF NATURAL GAS SERVICES GROUP, INC. AND HEREBY MAKES PAYMENT OF $3.25 PER
SHARE IN PAYMENT OF THE EXERCISE PRICE THEREOF.

                     INSTRUCTIONS FOR REGISTRATION OF STOCK

NAME:

--------------------------------------------------------------------------------
                     (PLEASE TYPE OR PRINT IN BLOCK LETTERS)
ADDRESS:

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

SIGNATURE
         ------------------------------------------------------

DATED:
       ------------------,-------

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

                                 ASSIGNMENT FORM

      FOR VALUE RECEIVED, __________________________, HEREBY SELLS, ASSIGNS
      AND TRANSFERS UNTO

NAME:

--------------------------------------------------------------------------------
                     (PLEASE TYPE OR PRINT IN BLOCK LETTERS)
ADDRESS:

--------------------------------------------------------------------------------
THE RIGHT TO PURCHASE SHARES OF NATURAL GAS SERVICES GROUP, INC. REPRESENTED BY
THIS WARRANT CERTIFICATE TO THE EXTENT OF _________ SHARES AS TO WHICH SUCH
RIGHT IS EXERCISABLE AND DOES HEREBY IRREVOCABLY CONSTITUTE AND APPOINT NATURAL
GAS SERVICES GROUP, INC. TO TRANSFER THE SAME ON THE BOOKS OF THE COMPANY WITH
FULL POWER OF SUBSTITUTION IN THE PREMISES.

SIGNATURE
         ------------------------------------------------------

DATED:
       ------------------,-------

                                    NOTICE: THE SIGNATURE OF THIS ASSIGNMENT
                                    MUST CORRESPOND WITH THE NAME AS IT APPEARS
                                    UPON THE FACE OF THIS WARRANT CERTIFICATE IN
                                    EVERY PARTICULAR, WITHOUT ALTERATION OR
                                    ENLARGEMENT OR ANY CHANGE WHATEVER.
<PAGE>
                                                                       EXHIBIT B

                        WARRANT CONVERSION EXERCISE FORM

TO: NATURAL GAS SERVICES GROUP, INC.

     Pursuant to Section 2.3 of the Warrant Certificate from Natural Gas
Services Group, Inc. (the "Company") to the undersigned Holder, the Holder
hereby irrevocably elects to convert Warrants with respect to Shares of the
Company into ___________ Shares of the Company.

A conversion calculation is attached hereto as Exhibit B-1.

     The undersigned requests that certificates for such Shares be issued as
follows:

     Name:
                  ------------------------------------------
     Address:
                  ------------------------------------------
     Deliver to:
                  ------------------------------------------

and that a new Warrant Certificate for the balance remaining of the Warrants, if
any, subject to the Warrant be registered in the name of, and delivered to, the
undersigned at the address stated above.

     Dated:
                  --------------------------

                                                        ------------------------
                                                        [NAME OF WARRANT HOLDER]
<PAGE>
                                                                     EXHIBIT B-1

                        CALCULATION OF WARRANT CONVERSION

Shares to be Delivered by Company     =      Net Value
                                             _________
                                                fmv

                              fmv     =      $____________

                        Net Value     =      aggregate fmv of Converted Shares -
                                             aggregate Exercise Price of
                                             Converted Shares

                                      =      $____________ - $____________

                                      =      $____________

Shares to be Delivered by Company     =      _____________

                Fractional Shares     =      ____________

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