Document:

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                                                                    Exhibit 4.03

                                  April , 2002

Neidiger, Tucker, Bruner, Inc.
1675 Larimer Street, Suite 300
Denver, Colorado  80202

         Re:      Natural Gas Services Group, Inc.

Ladies and Gentlemen:

         Reference is made to a proposed public offering of shares of common
stock and warrants (the "Public Securities") by Natural Gas Services Group, Inc.
(the "Company") pursuant to a Registration Statement (the "Registration
Statement") and prospectus included therein to be filed with the Securities and
Exchange Commission and to be underwritten by Neidiger/Tucker/Bruner, Inc. as
the managing underwriter (the "Underwriter") named in an underwriting agreement.

         In consideration of the offer and sale of the Public Securities by the
Company and the Underwriter and of other valuable consideration, the receipt of
which is hereby acknowledged, the undersigned agrees not to offer, sell
(including engaging in a short sale), contract to sell, pledge, hypothecate,
grant any option to purchase or otherwise dispose of any shares of common stock
of the Company or any securities convertible into or exchangeable for common
stock of the Company beneficially owned or otherwise held by the undersigned as
of the date of this letter or acquired on or prior to the date of effectiveness
of the Registration Statement or issuable upon exercise of options or warrants
held by the undersigned on such dates (collectively, the "Shares") for the
period specified hereafter without the prior written consent of the Underwriter.
Such restrictions shall apply to the total number of Shares held by the
undersigned for a period of one year after the date of the effective date of the
Registration Statement.

         As a reasonable means of ensuring compliance with the terms of this
Agreement, the undersigned further agrees that the Company may instruct the
transfer agent for the Shares to place a transfer restriction on such transfer
agent's records.

         Notwithstanding the foregoing, if the undersigned is an individual, he
or she may transfer any or all of the Shares either during his or her lifetime
or on death by will or intestacy to his or her immediate family or to a trust,
the beneficiaries of which are exclusively the undersigned and/or a member or
members of his or her immediate family; provided, however, that in any such case
it shall be a condition to the transfer that the transferee execute an agreement
stating that the transferee is receiving and holding the Shares subject to the
provisions of this Agreement, and there shall be no further transfer of such
Shares except in accordance with this

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Neidiger/Tucker/Bruner, Inc.
Agreement Not To Sell
Page 2

Agreement. For purposes of this paragraph, "immediate family" shall mean spouse,
lineal descendant, father, mother, brother or sister of the transferor.

         In addition, notwithstanding the foregoing, if the undersigned is a
partnership, the partnership may transfer any Shares to a partner of such
partnership or a retired partner of such partnership who retires after the date
hereof, or to the estate of any such partner or retired partner, and any partner
who is an individual may transfer Shares by gift, will or intestate succession
to his or her immediate family (as defined above) or ancestors; and if the
undersigned is a corporation, the corporation may transfer Shares to any
shareholder of such corporation and any shareholder who is an individual may
transfer Shares by gift, will or intestate succession to his or her immediate
family (as defined above) or ancestors; provided, however, that in any such
case, it shall be a condition to the transfer that the transferee execute an
agreement stating that the transferee is receiving and holding the Shares
subject to the provisions of this Agreement, and there shall be no further
transfer of such Shares except in accordance with this Agreement.

         Finally, notwithstanding the foregoing, the Underwriter, in its sole
discretion, may release from this Agreement any or all of the Shares or release
from any agreement similar to this Agreement any shares of common stock owned by
any other shareholder of the Company. Any such release must be in a writing
signed by the Underwriter.

         This agreement shall be enforceable by the Company and the Underwriter,
or either of them, and shall bind and inure to the benefit of their respective
successors, personal representatives, heirs, and assigns.

                                           Very truly yours,

                                           By:
_______________________________                ________________________________
Shares of common stock subject                 Signature
to this Agreement

                                           _____________________________________
                                             Printed name of person or entity

                                           _____________________________________
                                               Title if signing for an entity<PAGE>

                                                                    Exhibit 4.04

THE REPRESENTATIVE'S OPTION EVIDENCED AND REPRESENTED BY THIS CERTIFICATE (THE
"REPRESENTATIVE'S OPTION") AND THE SECURITIES ISSUABLE UPON EXERCISE HEREOF (THE
"OPTION SHARES") HAVE BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED, PURSUANT TO A REGISTRATION STATEMENT FILED WITH THE SECURITIES AND
EXCHANGE COMMISSION AND WITH THE SECURITIES ADMINISTRATORS OF CERTAIN STATES
UNDER THE SECURITIES ("BLUE SKY") LAWS OF SUCH STATES. HOWEVER, NEITHER THE
REPRESENTATIVE'S OPTION NOR THE UNDERLYING COMMON STOCK MAY BE SOLD,
TRANSFERRED, PLEDGED, OR HYPOTHECATED EXCEPT PURSUANT TO (I) A POST-EFFECTIVE
AMENDMENT TO SUCH REGISTRATION STATEMENT, (II) A SEPARATE REGISTRATION STATEMENT
UNDER SUCH ACT, OR (III) AN EXEMPTION FROM REGISTRATION UNDER SUCH ACT AND UNDER
THE APPLICABLE BLUE SKY LAWS.

THIS REPRESENTATIVE'S OPTION MAY NOT BE SOLD, TRANSFERRED OR ASSIGNED EXCEPT AS
OTHERWISE PROVIDED HEREIN AND THE HOLDER OF THIS REPRESENTATIVE'S OPTION, BY ITS
ACCEPTANCE HEREOF, AGREES THAT IT WILL NOT SELL, TRANSFER OR ASSIGN THIS
REPRESENTATIVE'S OPTION EXCEPT AS OTHERWISE PROVIDED HEREIN.

                        NATURAL GAS SERVICES GROUP, INC.

            REPRESENTATIVE'S OPTION FOR THE PURCHASE OF COMMON STOCK

NO. UW-001                                      165,000 REPRESENTATIVE'S OPTION

         THIS CERTIFIES that, for receipt in hand of $50 and other value
received, NEIDIGER/TUCKER/BRUNER, INC. (the "Holder"), is entitled to subscribe
for and purchase from NATURAL GAS SERVICES GROUP, INC., a Colorado corporation
(the "Company"), upon the terms and conditions set forth herein, at any time, or
from time to time, after _________, 2003, and before 5:00 p.m. Colorado time on
__________, 2007 (the "Exercise Period"), 165,000 shares of Common Stock (the
"Option Shares"), at a price of $_________ per Warrant Share (the "Exercise
Price"), or 120% of the offering price of Common Stock to be sold by the Company
in a public offering under Registration Statement Form SB-2, No. 333-_______
(the "Public Offering") at or prior to the date hereof.

         The term the "Holder" as used herein shall include any transferee to
whom this Representative's Option has been transferred in accordance with the
terms of this Representative's Option. As used herein the term "this
Representative's Option" shall mean and include this Representative's Option and
any Representative's Option or Representative's Options hereafter issued as a
consequence of the exercise or transfer of this Representative's

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Option in whole or in part, and the term "Common Stock" shall mean and include
the Company's Common Stock with ordinary voting power, which class at the date
hereof is publicly traded.

         1. This Representative's Option may not be sold, transferred, assigned,
pledged or hypothecated until ________, 2003 (one year after the effective date
of the registration statement on which it is initially registered) except that
it may be transferred, in whole or in part, (i) to one or more officers or
partners of the holder (or the officers or partners of any such partner); (ii)
to a member of the underwriting syndicate and/or its officers or partners; (iii)
by reason of reorganization of the company; or (iv) by operation of law. After
_________, 2003, this Representative's Option may be sold, transferred, assigned
or hypothecated in accordance with applicable law.

                  2. (a) This Representative's Option may be exercised during
         the Exercise Period as to the whole or any lesser number of Option
         Shares, by the surrender of this Representative's Option (with the
         election attached hereto duly executed) to the Company at its office at
         2911 South County Road 1260, Midland, Texas 79706, or such other place
         as is designated in writing by the Company, together with a certified
         or bank cashier's check payable to the order of the Company in an
         amount equal to the Exercise Price multiplied by the number of Option
         Shares for which this Representative's Option is being exercised.

                  (b) Upon written request of the Holder, and in lieu of payment
         for the Option Shares by check in accordance with paragraph 2(a)
         hereof, the Holder may exercise the Representative's Option (or any
         portion thereof) for and receive the number of Option Shares equal to a
         fraction, the numerator of which equals (i) the amount by which the
         Current Market Price of the Common Stock for the ten (10) trading days
         preceding the date of exercise exceeds the Exercise Price per Share,
         multiplied by (ii) the number of Option Shares to be purchased; the
         denominator of which equals the Current Market Price.

                  (c) For the purposes of any computation under this
         Representative's Option, the "Current Market Price" at any date shall
         be the closing price of the Common Stock on

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         the business day next preceding the event requiring an adjustment
         hereunder. If the principal trading market for such securities is an
         exchange, the closing price shall be the reported last sale price on
         such exchange on such day provided if trading of such Common Stock is
         listed on any consolidated tape, the closing price shall be the
         reported last sale price set forth on such consolidated tape. If the
         principal trading market for such securities is the over-the-counter
         market, the closing price shall be the last reported sale price on such
         date as set forth by the American Stock Exchange, or, if the security
         is not quoted on such market, the average closing bid and asked prices
         as set forth in the National Quotation Bureau pink sheet or the
         Electronic Bulletin Board System for such day. Notwithstanding the
         foregoing, if there is no reported last sale price or average closing
         bid and asked prices, as the case may be, on a date prior to the event
         requiring an adjustment hereunder, then the current market price shall
         be determined as of the latest date prior to such day for which such
         last sale price or average closing bid and asked price is available.

         3. Upon each exercise of this Representative's Option, the Holder shall
be deemed to be the holder of record of the Option Shares issuable upon such
exercise, notwithstanding that the transfer books of the Company shall then be
closed or certificates representing such Option Shares shall not then have been
actually delivered to the Holder. As soon as practicable after each such
exercise of this Representative's Option, the Company shall issue and deliver to
the Holder a certificate or certificates for the Option Shares issuable upon
such exercise, registered in the name of the Holder or its designee. If this
Representative's Option should be exercised in part only, the Company shall,
upon surrender of this Representative's Option for cancellation, execute and
deliver a new Representative's Option evidencing the right of the Holder to
purchase the balance of the Option Shares (or portions thereof) subject to
purchase hereunder.

         4. The Representative's Option shall be registered in a
Representative's Option Register as they are issued. The Company shall be
entitled to treat the registered holder of any Representative's Option on the
Representative's Option Register 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 Representative's Option on the part of any other person. The
Representative's Option shall be transferable only on the books of the Company
upon delivery thereof duly endorsed by the

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Holder or by his duly authorized attorney or representative, or accompanied by
proper evidence of succession, assignment or authority to transfer. In all cases
of transfer by an attorney, executor, administrator, guardian or other legal
representative, duly authenticated evidence of his or its authority shall be
produced. Upon any registration of transfer, the Company shall deliver a new
Representative's Option or Representative's Options to the person entitled
thereto. The Representative's Option may be exchanged, at the option of the
Holder thereof, for another Representative's Option, or other Representative's
Option of different denominations, of like tenor and representing in the
aggregate the right to purchase a like number of Option Shares (or portions
thereof) upon surrender to the Company or its duly authorized agent.
Notwithstanding the foregoing, the Company shall have no obligation to cause
Representative's Option to be transferred on its books to any person if, in the
opinion of counsel to the Company, such transfer does not comply with the
provisions of the Securities Act of 1933, as amended (the "Act"), or applicable
state blue sky laws and the rules and regulations thereunder.

         5. The Company shall at all times reserve and keep available out of its
authorized and unissued Common Stock, solely for the purpose of providing for
the exercise of this Representative's Option, such number of shares of Common
Stock as shall, from time to time, be sufficient therefor. The Company covenants
that all Option Shares issuable upon exercise of this Representative's Option
shall be validly issued, fully paid, nonassessable, and free of preemptive
rights.

         6. (a) If the Company shall at any time subdivide its outstanding
         Common Stock by recapitalization, reclassification or split-up thereof,
         the number of Option Shares subject to this Representative's Option
         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 Option Shares subject to this Representative's
         Option 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.

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                  (b) If the Company after the date hereof shall distribute to
         the holders of its Common Stock any securities or other assets (other
         than a distribution of Common Stock or a cash distribution made as a
         dividend payable out of earnings or out of any earned surplus legally
         available for dividends under the laws of the jurisdiction of
         incorporation of the Company), the Board of Directors shall be required
         to make such equitable adjustment in the Exercise Price in effect
         immediately prior to the record date of such distribution as may be
         necessary to preserve the rights substantially proportionate to those
         enjoyed hereunder by the Holder immediately prior to such distribution.
         Any such adjustment made in good faith by the Board of Directors shall
         be final and binding upon the Holder and shall become effective as of
         the record date for such distribution.

                  (c) No adjustment in the number of Option Shares subject to
         this Representative's Option shall be required unless such adjustment
         would require an increase or decrease in such number of Option Shares
         of at least 1% of the then adjusted number of Option Shares issuable
         upon exercise of this Representative's Option, provided, however, that
         any adjustments which by reason of the foregoing are not required at
         the time to be made shall be carried forward and taken into account and
         included in determining the amount of any subsequent adjustment; and
         provided further, however, that in case the Company shall at any time
         subdivide or combine the outstanding Common Stock or issue any
         additional Common Stock as a dividend, said percentage shall forthwith
         be proportionately increased in the case of a combination or decreased
         in the case of a subdivision or dividend of Common Stock so as to
         appropriately reflect the same. If the Company shall make a record of
         the holders of its Common Stock for the purpose of entitling them to
         receive any dividend or distribution

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         and legally abandon its plan to pay or deliver such dividend or
         distribution then no adjustment in the number of Option Shares subject
         to this Representative's Option shall be required by reason of the
         making of such record.

                  (d) Whenever the number of Option Shares purchasable upon the
         exercise of this Representative's Option is adjusted as provided
         herein, the Exercise Price shall be adjusted (to the nearest one tenth
         of a cent) by respectively multiplying such Exercise Price immediately
         prior to such adjustment by a fraction, the numerator of which shall be
         the number of Option Shares purchasable upon the exercise of this
         Representative's Option immediately prior to such adjustment, and the
         denominator of which shall be the number of Option Shares purchasable
         immediately thereafter.

                  (e) In case of any reclassification of the outstanding Common
         Stock (other than a change covered by (a) hereof or which solely
         affects the par value of such Common Stock) or in the case of any
         merger or consolidation of the Company with or into another corporation
         (other than a consolidation or merger in which the Company is the
         continuing corporation and which does not result in any
         reclassification or capital reorganization of the outstanding Common
         Stock), or in the case of any sale or conveyance to another corporation
         of the property of the Company as an entirety or substantially as an
         entirety in connection with which the Company is dissolved, the Holder
         of this Representative's Option shall have the right thereafter (until
         the expiration of the right of exercise of this Representative's
         Option) to receive upon the exercise hereof, for the same aggregate
         Exercise Price payable hereunder immediately prior to such event, the
         kind and amount of shares of stock or other securities or property
         receivable upon such reclassification, capital reorganization, merger
         or consolidation, or

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         upon the dissolution following any sale or other transfer, by a holder
         of the number of Option Shares obtainable upon the exercise of this
         Representative's Option immediately prior to such event; and if any
         reclassification also results in a change in Common Stock covered by
         (a) above, then such adjustment shall be made pursuant to both this
         paragraph (e) and paragraph (a). The provisions of this paragraph (e)
         shall similarly apply to successive re-classifications, or capital
         reorganizations, mergers or consolidations, sales or other transfers.

         If the Company after the date hereof shall issue or agree to issue
Common Stock, Options or Convertible Securities, other than as described herein,
and such issuance or agreement would in the opinion of the Board of Directors of
the Company materially affect the rights of the Holders of the Representative's
Option, the Exercise Price and the number of Option Shares purchasable upon
exercise of the Representative's Option shall be adjusted in such matter, if
any, and at such time as the Board of Directors of the Company, in good faith,
may determine to be equitable in the circumstances. The minutes or unanimous
consent approving such action shall set forth the Board of Director's
determination as to whether an adjustment is warranted and the manner of such
adjustment. In the absence of such determination, any Holder may request in
writing that the Board of Directors make such determination. Any such
determination made in good faith by the Board of Directors shall be final and
binding upon the Holders. If the Board fails, however, to make such
determination within sixty (60) days after such request, such failure shall be
deemed a determination that an adjustment is required.

                           (i) Upon occurrence of each event requiring an
                  adjustment of the Exercise Price and of the number of Option
                  Shares purchasable upon exercise of this Representative's
                  Option in accordance with, and as required by, the terms
                  hereof, the Company shall forthwith employ a firm of certified
                  public accountants (who may be the regular accountants for the
                  Company) who shall compute the adjusted Exercise Price and the
                  adjusted number of Option Shares purchasable at such adjusted
                  Exercise Price by reason of such event in accordance herewith.
                  The Company shall give to each Holder of the Representative's
                  Option a copy of such

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                  computation which shall be conclusive and shall be binding
                  upon such Holders unless contested by Holders by written
                  notice to the Company within thirty (30) days after receipt
                  thereof.

                           (ii) In case the Company after the date hereof shall
                  propose (A) to pay any dividend payable in stock to the
                  holders of its Common Stock or to make any other distribution
                  (other than cash dividends) to the holders of its Common Stock
                  or to grant rights to subscribe to or purchase any additional
                  shares of any class or any other rights or options, (B) to
                  effect any reclassification involving merely the subdivision
                  or combination of outstanding Common Stock, or (C) any capital
                  reorganization or any consolidation or merger, or any sale,
                  transfer or other disposition of its property, assets and
                  business substantially as an entirety, or the liquidation,
                  dissolution or winding up of the Company, then in each such
                  case, the Company shall obtain the computation described above
                  and if an adjustment to the Exercise Price is required, the
                  Company shall notify the Holders of the Representative's
                  Option of such proposed action, which shall specify the record
                  date for any such action or if no record date is established
                  with respect thereto, the date on which such action shall
                  occur or commence, or the date of participation therein by the
                  holders of Common Stock if any such date is to be fixed, and
                  shall also set forth such facts with respect thereto as shall
                  be reasonably necessary to indicate the effect of such action
                  on the Exercise Price and the number, or kind, or class of
                  shares or other securities or property obtainable upon
                  exercise of this Representative's Option after giving effect
                  to any adjustment which will be required as a result of such
                  action. Such notice shall be given at least twenty (20) days
                  prior to the record date for determining holders of the Common
                  Stock for purposes of any such action, and in the case of any
                  action for which a record date is not established then such
                  notice shall be mailed at least twenty (20) days prior to the
                  taking of such proposed action.

                           (iii) Failure to file any certificate or notice or to
                  give any notice, or any defect in any certificate or notice,
                  shall not effect the legality or validity of the adjustment in
                  the Exercise Price or in the number, or kind, or class of
                  shares or

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                  other securities or property obtainable upon exercise of the
                  Representative's Option or of any transaction giving rise
                  thereto.

                  (f) The Company shall not be required to issue fractional
         Option Shares upon any exercise of the Representative's Option. As to
         any final fraction of a Share which the Holder of a Representative's
         Option 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 Current Market Price of
         a share of such stock on the business day preceding the day of
         exercise. The Holder of a Representative's Option, by his acceptance of
         a Representative's Option, expressly waives any right to receive any
         fractional Option Shares.

                  (g) Regardless of any adjustments pursuant to this section in
         the Exercise Price or in the number, or kind, or class of shares or
         other securities or other property obtainable upon exercise of a
         Representative's Option, a Representative's Option may continue to
         express the Exercise Price and the number of Option Shares obtainable
         upon exercise at the same price and number of Option Shares as are
         stated herein.

                  (h) The number of Option Shares, the Exercise Price and all
         other terms and provisions of the Company's agreement with the Holder
         of this Representative's Option shall be determined exclusively
         pursuant to the provisions hereof.

                  (i) The above provisions of this section 6 shall similarly
         apply to successive transactions which require adjustments.

                  (j) Notwithstanding any other language to the contrary herein,
         (i) the anti-dilution terms of this Representative's Option will not be
         enforced so as to provide the Holder the right to receive, or for the
         accrual of, cash dividends prior to the exercise of

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         this Representative's Option, and (ii) the anti-dilution terms of this
         Representative's Option will not be enforced in such a manner as to
         provide the Holder with disproportionate rights, privileges and
         economic benefits not provided to purchasers of the Common Stock in the
         Public Offering.

         7. The issuance of any Option Shares or other securities upon the
exercise of this Representative's Option and the delivery of certificates or
other instruments representing such securities, or other securities, shall be
made without charge to the Holder for any tax or other charge in respect of such
issuance. The Company shall not, however, be required to pay any tax which may
be payable in respect of any transfer involved in the issue and delivery of any
certificate in a name other than that of the Holder and the Company shall not be
required to issue or deliver any such certificate unless and until the person or
persons requesting the issue thereof shall have paid to the Company the amount
of such tax or shall have established to the satisfaction of the Company that
such tax has been paid.

         8. (a) If, at any time after _____________, 2003 (one year after the
         Effective Date of the Registration Statement), and ending ____________,
         2008 (six years after the Effective Date of the Registration
         Statement), the Company shall file a registration statement (other than
         on Form S-4, Form S-8, or any successor form) with the Securities and
         Exchange Commission (the "Commission") while Option Shares are
         available for purchase upon exercise of this Representative's Option or
         while any Option Shares (collectively, the "Representative's Option and
         the underlying Option Shares, the "Representative's Securities") are
         outstanding, the Company shall, on one occasion only, give the Holder
         and all the then holders of such Representative's Securities at least
         30 days prior written notice of the filing of such registration
         statement. If requested by the Holder or by any such holder in writing
         within 20 days after receipt of any such notice, the Company shall, at
         the Company's sole expense (other than the fees and disbursements of
         counsel for the Holder or such holder and the underwriting discounts
         and non-accountable expenses, if any, payable in respect of the
         securities sold by the Holder or any such holder), register or qualify
         the Option Shares of the Holder or any such holders who shall have made
         such request concurrently with the registration of such other

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         securities, all to the extent requisite to permit the public offering
         and sale of the Option Shares requested to be registered, and will use
         its best efforts through its officers, directors, auditors and counsel
         to cause such registration statement to become effective as promptly as
         practicable. Notwithstanding the foregoing, if the managing underwriter
         of any such offering shall advise the Company in writing that, in its
         opinion, the distribution of all or a portion of the Option Shares
         requested to be included in the registration concurrently with the
         securities being registered by the Company would materially adversely
         affect the distribution of such securities by the Company for its own
         account, then the Holder or any such holder who shall have requested
         registration of his or its Option Shares shall delay the offering and
         sale of such Option Shares (or the portions thereof so designated by
         such managing underwriter) for such period, not to exceed 90 days, as
         the managing underwriter shall request, provided that no such delay
         shall be required as to any Option Shares if any securities of the
         Company are included in such registration statement for the account of
         any person other than the Company and the Holder unless the securities
         included in such registration statement for such other person shall
         have been reduced pro rata to the reduction of the Option Shares which
         were requested to be included in such registration.

                  (b) If at any time after __________, 2003 (one year after the
         Effective Date of the Registration Statement), and before ___________,
         2007 (five years after the Effective Date of the Registration
         Statement), the Company shall receive a written request from holders of
         Representative's Securities who, in the aggregate, own (or upon
         exercise of all Option Shares will own) a majority of the total number
         of Option Shares, the Company shall, as promptly as practicable,
         prepare and file with the Commission a registration statement
         sufficient to permit the public offering and sale of the Option Shares,
         and will use its best efforts through its officers, directors, auditors
         and counsel to cause such registration statement to become effective as
         promptly as practicable; provided, however, that the Company shall only
         be obligated to file and obtain effectiveness of one such registration
         statement for which all expenses incurred in connection with such
         registration (other than the fees and disbursements of counsel for the
         Holder or such holders and underwriting discounts and nonaccountable
         expenses, if any, payable in

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         respect of the Option Shares sold by the Holder or any such holder)
         shall be borne by the Company.

                  (c) In the event of a registration pursuant to the provisions
         of this paragraph 8, the Company shall use its best efforts to cause
         the Option Shares so requested to be registered or qualified for sale
         under the securities or blue sky laws of such jurisdictions as the
         Holder or such holders may reasonably request; provided, however, that
         the Company shall not be required to qualify to do business in any
         state by reason of this paragraph 8(c) in which it is not otherwise
         required to qualify to do business and provided further, that the
         Company has no obligation to qualify the Option Shares where such
         qualification would cause any unreasonable delay or expenditure by the
         Company.

                  (d) The Company shall keep effective any registration or
         qualification contemplated by this paragraph 8 and shall from time to
         time amend or supplement each applicable registration statement,
         preliminary prospectus, final prospectus, application, document and
         communication for such period of time as shall be required to permit
         the Holder or such holders to complete the offer and sale of the Option
         Shares covered thereby. The Company shall in no event be required to
         keep any such registration or qualification in effect for a period in
         excess of nine months from the date on which the Holder and such
         holders are first free to sell such Option Shares; provided, however,
         that if the Company is required to keep any such registration or
         qualification in effect with respect to securities other than the
         Option Shares beyond such period, the Company shall keep such
         registration or qualification in effect as it relates to the Option
         Shares for so long as such registration or qualification remains or is
         required to remain in effect in respect of such other securities.

                  (e) In the event of a registration pursuant to the provisions
         of this paragraph 8, the Company shall furnish to the Holder and to
         each such holder such reasonable number of copies of the registration
         statement and of each amendment and supplement thereto (in each case,
         including all exhibits), such reasonable number of copies of each
         prospectus contained in such registration statement and each supplement
         or amendment thereto (including each preliminary prospectus), all of
         which shall conform to the requirements

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         of the Act and the rules and regulations thereunder, and such other
         documents as the Holder or such holders may reasonably request in order
         to facilitate the disposition of the Option Shares included in such
         registration.

                  (f) In the event of a registration pursuant to the provisions
         of this paragraph 8, the Company shall furnish the Holder and each
         holder of any Option Shares so registered with an opinion of its
         counsel to the effect that (i) the registration statement has become
         effective under the Act and no order suspending the effectiveness of
         the registration statement, preventing or suspending the use of the
         registration statement, any preliminary prospectus, any final
         prospectus, or any amendment or supplement thereto has been issued, nor
         to such counsel's actual knowledge has the Securities and Exchange
         Commission or any securities or blue sky authority of any jurisdiction
         instituted or threatened to institute any proceedings with respect to
         such an order and (ii) the registration statement and each prospectus
         forming a part thereof (including each preliminary prospectus), and any
         amendment or supplement thereto, complies as to form with the Act and
         the rules and regulations thereunder. Such counsel shall also provide a
         Blue Sky Memorandum setting forth the jurisdictions in which the Option
         Shares have been registered or qualified for sale pursuant to the
         provisions of paragraph 8(c).

                  (g) The Company agrees that until all the Option Shares have
         been sold under a registration statement or pursuant to Rule 144 under
         the Act, or until the Option Shares may be sold under Rule 144 (k), it
         shall keep current in filing all reports, statements and other
         materials required to be filed with the Commission to permit holders of
         the Option Shares to sell such securities under Rule 144.

                  (h) The Holder and any holders who propose to register their
         Option Shares under the Act, shall execute and deliver to the Company a
         selling stockholder questionnaire on a form to be provided by the
         Company.

         (i) The Company shall not be required by the terms hereof to file a
         Registration Statement if, in the opinion of counsel to the holders of
         the Option Shares and counsel for the Company (or, should they not
         agree, in the opinion of another counsel experienced in securities law
         matters acceptable to counsel for the holders of Option Shares and the

                                       13
<PAGE>

         Company), the proposed public offering or other transfer as to which
         such Registration Statement is requested to be filed is exempt from
         applicable federal and state securities laws, rules, regulations and
         would result in unaffiliated purchasers or transferees obtaining
         securities that are not "restricted securities" as that term is defined
         in Rule 144 under the Act.

                  (a) Subject to the conditions set forth below, the Company
         agrees to indemnify and hold harmless the Holder, any holder of any of
         the Representative's Securities, their officers, directors, partners,
         employees, agents and counsel, and each person, if any, who controls
         any such person within the meaning of Section 15 of the Act or Section
         20(a) of the Securities Exchange Act of 1934, as amended (the "Exchange
         Act"), from and against any and all loss, liability, charge, claim,
         damage and expense whatsoever (which shall include, for all purposes of
         this Section 9, but not be limited to, attorneys' fees and any and all
         expense whatsoever incurred in investigating, preparing or defending
         against any litigation, commenced or threatened, or any claim
         whatsoever, and any and all amounts paid in settlement of any claim or
         litigation), as and when incurred, arising out of, based upon, or in
         connection with (i) any untrue statement or alleged untrue statement of
         a material fact contained (A) in any registration statement,
         preliminary prospectus or final prospectus (as from time to time
         amended and supplemented), or any amendment or supplement thereto, or
         (B) in any application or other document or communication (in this
         Section 9 collectively called an "application") executed by or on
         behalf of the Company or based upon written information furnished by or
         on behalf of the Company filed in any jurisdiction in order to register
         or qualify any of the Option Shares under the securities or blue sky
         laws thereof or filed with the Commission or any securities exchange;
         or any omission or alleged omission to state a material fact required
         to be stated therein or necessary to make the statements therein not
         misleading, unless such statement or omission was made in reliance upon
         and in conformity with written information furnished to the Company
         with respect to the Holder or any holder of any of the Representative's
         Securities by or on behalf of such person expressly for inclusion in
         any registration statement, preliminary prospectus, or final
         prospectus, or any amendment or supplement thereto, or in any
         application, as the case may be, or (ii) any breach of any
         representation, warranty, covenant or agreement of the

                                       14
<PAGE>

         Company contained in this Representative's Option. The foregoing
         agreement to indemnify shall be in addition to any liability the
         Company may otherwise have, including liabilities arising under this
         Representative's Option. If any action is brought against the Holder or
         any holder of any of the Representative's Securities or any of its
         officers, directors, partners, employees, agents or counsel, or any
         controlling persons of such person (an "indemnified party") in respect
         of which indemnity may be sought against the Company pursuant to the
         foregoing paragraph, such indemnified party or parties shall promptly
         notify the Company in writing of the institution of such action (but
         the failure so to notify shall not relieve the Company from any
         liability it may otherwise have to Holder or any holder of any of the
         Representative's Securities) and the Company shall promptly assume the
         defense of such action, including the employment of counsel (reasonably
         satisfactory to such indemnified party or parties) and payment of
         expenses. Such indemnified party or parties shall have the right to
         employ its or their own counsel in any such case, but the fees and
         expenses of such counsel shall be at the expense of such indemnified
         party or parties unless the employment of such counsel shall have been
         authorized in writing by the Company in connection with the defense of
         such action or the Company shall not have promptly employed counsel
         reasonably satisfactory to such indemnified party or parties to have
         charge of the defense of such action or such indemnified party or
         parties shall have reasonably concluded that there may be one or more
         legal defenses available to it or them or to other indemnified parties
         which are different from or additional to those available to the
         Company, in any of which events such fees and expenses shall be borne
         by the Company and the Company shall not have the right to direct the
         defense of such action on behalf of the indemnified party or parties.
         Anything in this paragraph to the contrary notwithstanding, the Company
         shall not be liable for any settlement of any such claim or action
         effected without its written consent.

                  (b) The Holder and each holder agrees to indemnify and hold
         harmless the Company, each director of the Company, each officer of the
         Company who shall have signed any registration statement covering the
         Option Shares held by the Holder and each holder and each other person,
         if any, who controls the Company within the meaning of Section 15 of
         the Act or Section 20(a) of the Exchange Act, to the same extent as the
         foregoing indemnity from the Company to the Holder and each holder in
         paragraph 9(a),

                                       15
<PAGE>

         but only with respect to statements or omissions, if any, made in any
         registration statement, preliminary prospectus, or final prospectus (as
         from time to time amended and supplemented), or any amendment or
         supplement thereto, or in any application, in reliance upon and in
         conformity with written information furnished to the Company with
         respect to the Holder and each holder by or on behalf of the Holder and
         each holder expressly for inclusion in any such registration statement,
         preliminary prospectus, or final prospectus, or any amendment or
         supplement thereto, or in any application, as the case may be. If any
         action shall be brought against the Company or any other person so
         indemnified based on any such registration statement, preliminary
         prospectus, or final prospectus, or any amendment or supplement
         thereto, or in any application, and in respect of which indemnity may
         be sought against the Holder and each holder pursuant to this paragraph
         9(b), the Holder and each holder shall have the rights and duties given
         to the Company, and the Company and each other person so indemnified
         shall have the rights and duties given to the indemnified parties, by
         the provisions of paragraph 9(a).

                  (c) To provide for just and equitable contribution, if (i) an
         indemnified party makes a claim for indemnification pursuant to
         paragraph 9(a) or 9(b) (subject to the limitations thereof) but it is
         found in a final judicial determination, not subject to further appeal,
         that such indemnification may not be enforced in such case, even though
         this Agreement expressly provides for indemnification in such case, or
         (ii) any indemnified or indemnifying party seeks contribution under the
         Act, the Exchange Act or otherwise because the indemnification provided
         for in this Section 9 is for any reason held to be unenforceable by the
         Company and the Holder and any holder, then the Company (including for
         this purpose any contribution made by or on behalf of any director of
         the Company, any officer of the Company who signed any such
         registration statement and any controlling person of the Company), as
         one entity, and the Holder and any holder of any of the Option Shares
         included in such registration in the aggregate (including for this
         purpose any contribution by or on behalf of the Holder or any holder),
         as a second entity, shall contribute to the losses, liabilities,
         claims, damages and expenses whatsoever to which any of them may be
         subject, on the basis of relevant equitable considerations such as the
         relative fault of the Company and the Holder or any such holder in
         connection with the facts which resulted in such losses, liabilities,
         claims, damages and expenses. The

                                       16
<PAGE>

         relative fault, in the case of an untrue statement, alleged untrue
         statement, omission or alleged omission, shall be determined by, among
         other things, whether such statement, alleged statement, omission or
         alleged omission relates to information supplied by the Company, by the
         Holder or by any holder of Option Shares included in such registration,
         and the parties' relative intent, knowledge, access to information and
         opportunity to correct or prevent such statement, alleged statement,
         omission or alleged omission. The Company and the Holder agree that it
         would be unjust and inequitable if the respective obligations of the
         Company and the Holder for contribution were determined by pro rata or
         per capita allocation of the aggregate losses, liabilities, claims,
         damages and expenses (even if the Holder and the other indemnified
         parties were treated as one entity for such purpose) or by any other
         method of allocation that does not reflect the equitable considerations
         referred to in this paragraph 9(c). No person guilty of a fraudulent
         misrepresentation (within the meaning of Section 11(f) of the Act)
         shall be entitled to contribution from any person who is not guilty of
         such fraudulent misrepresentation. For purposes of this paragraph 9(c),
         each person, if any, who controls the Holder or any holder of any of
         the Representative's Securities within the meaning of Section 15 of the
         Act or Section 20(a) of the Exchange Act and each officer, director,
         partner, employee, agent and counsel of each such person, shall have
         the same rights to contribution as such person and each person, if any,
         who controls the Company within the meaning of Section 15 of the Act or
         Section 20(a) of the Exchange Act, each officer of the Company who
         shall have signed any such registration statement, and each director of
         the Company shall have the same rights to contribution as the Company,
         subject in each case to the provisions of this paragraph 9(c). Anything
         in this paragraph 9(c) to the contrary notwithstanding, no party shall
         be liable for contribution with respect to the settlement of any claim
         or action effected without its written consent. This paragraph 9(c) is
         intended to supersede any right to contribution under the Act, the
         Exchange Act or otherwise.

         10. Unless the Option Shares have been registered or an exemption from
such registration is available, the Option Shares issued upon exercise of this
Representative's Option shall be subject to a stop transfer order and the
certificate or certificates evidencing any such Option Shares shall bear the
following legend or a legend substantially similar thereto:

                                       17
<PAGE>

         THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
         1933, NOR HAVE THEY BEEN REGISTERED UNDER THE SECURITIES ("BLUE SKY")
         LAWS OF ANY STATE. THESE SECURITIES MAY NOT BE SOLD, TRANSFERRED,
         PLEDGED, OR HYPOTHECATED UNLESS THEY HAVE FIRST BEEN REGISTERED UNDER
         THE SECURITIES ACT OF 1933 AND UNDER THE APPLICABLE STATE SECURITIES
         ("BLUE SKY") LAWS OR UNLESS THE AVAILABILITY OF AN EXEMPTION FROM
         REGISTRATION UNDER SUCH ACT AND LAWS IS ESTABLISHED TO THE SATISFACTION
         OF THE COMPANY, WHICH MAY NECESSITATE A WRITTEN OPINION OF SELLER'S
         COUNSEL SATISFACTORY TO COMPANY COUNSEL.

         11. Upon receipt of evidence satisfactory to the Company of the loss,
theft, destruction or mutilation of any Representative's Option (and upon
surrender of any Representative's Option if mutilated), and upon reimbursement
of the Company's reasonable incidental expenses, the Company shall execute and
deliver to the Holder thereof a new Representative's Option of like date, tenor
and denomination.

         12. The Holder of any Representative's Option shall not have, solely on
account of such status, any rights of a stockholder of the Company, either at
law or in equity, or to any notice of meetings of stockholders or of any other
proceedings of the Company, except as provided in this Representative's Option.

                                       18
<PAGE>

                  13. This Representative's Option shall be construed in
         accordance with the laws of the State of Colorado, without giving
         effect to conflict of laws.

Dated:  ______________________, 2002

                                         NATURAL GAS SERVICES GROUP, INC.

                                         By:  _________________________________
                                         Wayne L. Vinson, President

[SEAL]

                                       19

<PAGE>

                               FORM OF ASSIGNMENT

                (To be executed by the registered holder if such
                     holder desires to transfer the attached
                            Representative's Option.)

         FOR VALUE RECEIVED, ___________________________________ hereby sells,
assigns and transfers unto ________________________ Representative's Option to
purchase __________ shares of Common Stock of Natural Gas Services Group, Inc.
(the "Company"), together with all right, title and interest therein, and does
hereby irrevocably constitute and appoint ____________________________ attorney
to transfer such Representative's Option on the books of the Company, with full
power of substitution.

Dated: ______________________

Signature: ____________________________________

Signature Guaranteed:

                                     NOTICE

         The signature on the foregoing Assignment must correspond to the name
as written upon the face of this Representative's Option in every particular,
without alteration or enlargement or any change whatsoever. Signature(s) must be
guaranteed by an eligible guarantor institution which is a participant in a
Securities Transfer Association recognized program.

<PAGE>

                              ELECTION TO EXERCISE

             (To be executed by the holder if such holder desires to
                 exercise the attached Representative's Option)

         The undersigned hereby exercises his or its rights to subscribe for
__________ shares of Common Stock covered by the within Representative's Option
(each as defined in the within Representative's Option) and tenders payment
herewith in the amount of $__________ in accordance with the terms thereof, and
requests that certificates for such Common Stock be issued in the name of, and
delivered to:

_______________________________________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________
  (Print Name, Address and Social Security or Tax Identification Number)

and, if such number of shares of Common Stock (or portions thereof) shall not be
all the Common Stock covered by the within Representative's Option, that a new
Representative's Option for the balance of the Representative's Option covered
by the within Representative's Option be registered in the name of, and
delivered to, the undersigned at the address stated below.

Name:  ________________________________________________________________________
                                   (Print)

Address: ______________________________________________________________________

________________________________________
               (Signature)

                                     NOTICE

         The signature on the foregoing Assignment must correspond to the name
as written upon the face of this Representative's Option in every particular,
without alteration or enlargement or any change whatsoever. Signature(s) must be
guaranteed by an eligible guarantor institution which is a participant in a
Securities Transfer Association recognized program.

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