As filed with the Securities and Exchange Commission on May 23, 2005     


                                                                No. 333 - 122687

                                                                                

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


                          PRE-EFFECTIVE AMENDMENT NO. 1
                                       TO
                                    FORM S-3



             REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

                        NATURAL GAS SERVICES GROUP, INC.
             (Exact name of registrant as specified in its charter)

                                     
           Colorado                                             75-2811855
(State or other jurisdiction of                              (I.R.S. Employer
incorporation or organization)                            Identification Number)

                                                       Stephen C. Taylor
      2911 South County Road 1260                 2911 South County Road 1260
         Midland, Texas 79706                        Midland, Texas 79706
           (432) 563-3974                               (432) 563-3974         
  (Address, including zip code, and         (Name, address, including zip code,
telephone number, including area code,     code and telephone number, including,
     of registrant's principal                area code of agent for service)
         executive offices)
                                   Copies to:
                                 David A. Thayer
                               Jackson Kelly PLLC
                          1099 18th Street, Suite 2150
                                Denver, CO 80202
                            Telephone: (303) 390-0003

     Approximate date of commencement of proposed sale to the public: As soon as
practicable after the effective date of this Registration Statement.

     If the only  securities  being  registered  on this Form are being  offered
pursuant to dividend or interest  reinvestment plans, please check the following
box. [ ]

     If any of the securities being registered on this Form are to be offered on
a delayed or continuous  basis  pursuant to Rule 415 under the Securities Act of
1933, other than securities offered only in connection with dividend or interest
reinvestment plans, check the following box. [X]

     If this form is filed to  register  additional  securities  for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list  the  Securities  Act  registration  statement  number  of the  earlier
effective registration statement for the same offering. [ ]

     If this form is a  post-effective  amendment  filed pursuant to Rule 462(c)
under the  Securities  Act,  check the following box and list the Securities Act
registration  statement number of the earlier effective  registration  statement
for the same offering. [ ]

     If delivery of the  prospectus is expected to be made pursuant to Rule 434,
please check the following box. [ ]





                         CALCULATION OF REGISTRATION FEE


==================================== ====================== ===================== ====================== ========================
                                                                                             
                                                                  Proposed              Proposed
                                            Amount                Maximum                Maximum
Title of Each Class of Securities            to be             Offering Price           Aggregate               Amount of
to be Registered                        Registered (1)         Per Share (2)       Offering Price (2)       Registration Fee
------------------------------------ ---------------------- --------------------- ---------------------- ------------------------
Common Stock, $.01 par value per
share                                       701,171                $10.35              $7,257,120               $855 (3)
==================================== ====================== ===================== ====================== ========================




(1)  Pursuant  to Rule  416 of the  Securities  Act of 1933,  this  registration
     statement shall cover such indeterminate number of additional shares of the
     Registrant's  Common Stock as may be issued as a result of stock dividends,
     stock  splits,  recapitalizations,  or  similar  transactions  prior to the
     termination of this registration statement.


(2)  Estimated  solely  for the  purpose of  calculating  the  registration  fee
     pursuant to Rule 457(c) under the Securities Act of 1933, as amended, based
     upon the closing price of the Registrant's Common Stock on May 18, 2005, as
     quoted on the American Stock Exchange.

(3)  $746 was previously paid. $109 is being paid with this Amendment No. 1.



     The Registrant  hereby amends this  registration  statement on such date or
dates as may be necessary to delay its effective date until the Registrant shall
file a further  amendment  which  specifically  states  that  this  registration
statement shall  thereafter  become effective in accordance with Section 8(a) of
the  Securities  Act of 1933 or until the  registration  statement  shall become
effective on such date as the Commission,  acting pursuant to said Section 8(a),
may determine.

================================================================================













     The information in this prospectus is not complete and may be changed.  The
selling  shareholders  may  not  sell  these  securities  in  reliance  on  this
prospectus  until the  registration  statement  filed  with the  Securities  and
Exchange  Commission,  of which this  prospectus is a part,  is effective.  This
prospectus is not an offer to sell these  securities and it is not soliciting an
offer to buy  these  securities  in any  state  where  the  offer or sale is not
permitted.



PROSPECTUS                SUBJECT TO COMPLETION, DATED
                                  May 23, 2005


                                 701,171 SHARES



                        NATURAL GAS SERVICES GROUP, INC.

                                  Common Stock


     This  prospectus  relates to 701,171 shares of our common stock that may be
offered for sale or  otherwise  transferred  from time to time by certain of our
shareholders.  See "Selling  Shareholders" on page 16. Of these shares,  118,968
shares are  outstanding as of the date of this  prospectus,  while the remaining
582,203  shares will be issuable  upon the  exercise of  warrants.  Warrants for
616,175  of the  shares  were  issued by us in early  2001 when we  completed  a
private  placement of units  consisting  of the  warrants  and 10%  subordinated
notes.  The  remaining  warrants  for 84,996 were issued in March 2001 and April
2002 to several of our affiliates in consideration for their personal guarantees
of  our  corporate  debt.  See  "SELLING  SHAREHOLDERS"  on  page  16  for  more
information concerning the issuance of the warrants.

     Our common stock is quoted on the American  Stock Exchange under the symbol
"NGS".  On May 18,  2005,  the closing sale price of our common stock was $10.35
per share.


     Our  principal  executive  office is located at 2911 S.  County  Road 1260,
Midland, Texas 79706 and the telephone number is (432) 563-3974.

     The selling  shareholders  may offer these shares from time to time through
public or private  transactions at market prices prevailing at the time of sale,
at prices related to prevailing market prices or at other negotiated prices. The
selling  shareholders  may sell none,  some or all of the shares offered by this
prospectus.  We cannot predict when or in what amounts the selling  shareholders
may sell any of the shares offered by this prospectus.  The selling shareholders
will  generally be responsible  for their legal fees and for any  commissions or
discounts due to brokers or dealers. We will pay the other offering expenses. We
will  not  receive  any of the  proceeds  from  the sale of  shares  by  selling
shareholders under this prospectus. See "Plan of Distribution" on page 16.


     PROSPECTIVE  PURCHASERS OF THE COMMON STOCK SHOULD  CONSIDER  CAREFULLY THE
MATTERS SET FORTH UNDER "RISK FACTORS" BEGINNING ON PAGE 4.


     Neither the  Securities and Exchange  Commission  nor any state  securities
commission has approved or  disapproved  of these shares,  or determined if this
prospectus  is truthful or  complete.  Any  representation  to the contrary is a
criminal offense.


                  The date of this Prospectus is May __, 2005.




                                                       
                    WHERE YOU CAN FIND ADDITIONAL INFORMATION

     We file annual,  quarterly and special reports,  proxy statements and other
information  with the Securities and Exchange  Commission (or SEC). You may read
and  copy  materials  that  we have  filed  with  the  Securities  and  Exchange
Commission at the following  Securities and Exchange Commission public reference
room:

                             450 Fifth Street, N.W.
                             Washington, D.C. 20549

     Please call the Securities and Exchange  Commission at  1-800-SEC-0330  for
further information on the public reference room.

     The shares of common stock of Natural Gas Services  Group are traded on the
American Stock Exchange under the symbol "NGS".

     Our  Securities and Exchange  Commission  filings are also available to the
public  on  the  Securities  and  Exchange   Commission's  internet  website  at
http://www.sec.gov.  In addition,  the filings  Natural Gas Services Group makes
with the Securities and Exchange  Commission are also available to the public on
Natural Gas Services Group's website, www.ngsgi.com.  Information on our website
is not incorporated into this prospectus and is not part of this prospectus.

     We have filed with the  Securities  and Exchange  Commission a registration
statement  on Form S-3  covering  the  shares  offered by this  prospectus.  The
registration statement,  including the attached exhibits and schedules, contains
additional  relevant  information  about us and our common stock, and you should
refer to the  applicable  exhibit or schedule for a complete  description of any
statement referring to any contract or other document. The rules and regulations
of the Securities and Exchange  Commission allow us to omit certain  information
included in the registration statement from this prospectus.


                     INCORPORATION OF DOCUMENTS BY REFERENCE

     The SEC allows us to  "incorporate  by reference"  some of the documents we
file with it. This means that we can disclose  important  information  to you by
referring you to those documents.  The information  incorporated by reference is
considered to be part of this  prospectus,  and  information  that we file later
with the SEC will  automatically  update and  supersede  this  information.  The
documents we incorporate by reference are:


     o    Our  Quarterly  Report on Form 10-QSB for the quarter  ended March 31,
          2005;

     o    Our Annual Report on Form 10-KSB for the year ended December 31, 2004;

     o    Our Current Reports on Form 8-K filed with the Securities and Exchange
          Commission  on January 7, 2005,  January 13,  2005,  January 26, 2005,
          February 24, 2005, March 18, 2005, and May 13, 2005;


     o    The  description of our common stock contained in Items 1 and 2 of our
          Registration  Statement  on Form 8-A  filed  under  Section  12 of the
          Securities  Exchange Act of 1934 (or  Exchange  Act) on July 17, 2002;
          and


                                       2


     o    All documents we file pursuant to Sections  13(a),  13(c), 14 or 15(d)
          of the Exchange Act after the date of this prospectus and prior to the
          termination of the offering of the shares offered hereby.

     We will provide at no cost to each person,  including any beneficial owner,
to whom this  prospectus  is  delivered,  on the written or oral request of such
person, a copy of any or all of the documents we incorporate by reference, other
than  exhibits  to  such  documents  (unless  those  exhibits  are  specifically
incorporated by reference into the documents that this prospectus incorporates).
Requests  should be directed to Natural Gas  Services  Group,  Inc.,  2911 South
County Road 1260,  Midland,  Texas 79706,  (432) 563-3974,  Attention:  Investor
Relations.

     We  have  not  authorized  anyone  to give  any  information  or  make  any
representation  about  us  that is  different  from,  or in  addition  to,  that
contained  in  this  prospectus  or  in  any  of  the  materials  that  we  have
incorporated by reference into this document. Therefore, if anyone does give you
information  of  this  sort,  you  should  not  rely  on  it.  If  you  are in a
jurisdiction  where offers to sell, or solicitations of offers to purchase,  the
shares of common stock  offered by this  document is  unlawful,  or if you are a
person to whom it is unlawful  to direct  these  types of  activities,  then the
offer  presented in this document does not extend to you. You should assume that
the  information  appearing in this  prospectus,  as well as the  information we
previously filed with the SEC and incorporated by reference, is accurate only as
of the date of the documents containing the information.

                     ABOUT NATURAL GAS SERVICES GROUP, INC.

     We provide  equipment and services to the natural gas and oil industry.  We
manufacture,  fabricate, sell and lease natural gas compressors that enhance the
production  of oil and gas wells and we provide  maintenance  services for those
compressors.  We define a natural gas compressor as a mechanical device with one
basic goal - to deliver gas at a pressure higher than that originally  existing.
It may be  powered  by a natural  gas  burning  engine or an  electric  motor to
accommodate different  applications.  Gas compression is undertaken to transport
and distribute  natural gas to pipelines.  Pipeline  pressures vary and with the
addition of new wells to the pipeline,  the need for compression  increases.  We
also  manufacture and sell flare tips and ignition systems for oil and gas plant
and production facilities. We define a flare tip as a burner on the upper end of
a flare  stack  that is  designed  to  combust  waste  gases  to  assure a clean
environment.  An  ignition  system is a pilot  light or a spark  generator  that
assures  continuous  ignition of the waste gases going through the burner in the
flare tip.


     We primarily lease and sell natural gas compressors.  As of March 31, 2005,
we had 661 natural gas compressors under lease to third parties.


     We also fabricate  natural gas  compressors  for our  customers,  designing
compressors to meet unique specifications dictated by well pressures, production
characteristics and particular applications for which compression is sought.

     We have  established  an exchange  and  rebuild  program to attempt to help
minimize  costs and maximize  revenue for our customers.  Under the program,  we
work  with  maintenance  and  operating  personnel  of a  customer  to  identify
equipment for exchange.  When we receive a compressor for exchange  because of a
maintenance problem, we deliver to our customer a replacement compressor at full
price. We then rebuild the exchange compressor and credit our customer an amount
based on the  value of the  rebuilt  compressor.  We also  offer a  retrofitting
service by repackaging a customer's  compressor with a compressor that meets our
customer's changed conditions.


                                       3


     We design,  manufacture,  install  and  service  flare  stacks and  related
ignition and control  devices for onshore and offshore  burning of gas compounds
such as hydrogen sulfide,  carbon dioxide,  natural gas and liquefied  petroleum
gases.

     We have  manufacturing  and  fabrication  facilities  located in  Lewiston,
Michigan,  Tulsa,  Oklahoma,  and  Midland,  Texas,  where  we  manufacture  and
fabricate natural gas compressors.  We design and manufacture  natural gas flare
systems,  components and ignition systems in our facility in Midland, Texas, for
use in oilfield,  refinery and petrochemical plant  applications.  On January 3,
2005, we acquired  Screw  Compression  Systems,  Inc., a Tulsa,  Oklahoma  based
manufacturer of natural gas compressors.

     We currently  provide our  products and services to a customer  base of oil
and gas exploration and production  companies  operating  primarily in Colorado,
Kansas, Louisiana, Michigan, New Mexico, Oklahoma, Texas and Wyoming.

     We maintain our principal  office at 2911 South County Road 1260,  Midland,
Texas 79706 and our telephone number is (432) 563-3974.


                                  RISK FACTORS

     To inform  investors of our future plans and  objectives,  this  prospectus
(and other  reports and  statements  issued by us and our officers  from time to
time) contain certain statements concerning our future performance,  intentions,
objectives,   plans  and   expectations   that  are  or  may  be  deemed  to  be
"forward-looking  statements." See "Forward Looking  Statements" on page 13. Our
ability to do this has been fostered by the Private Securities Litigation Reform
Act of 1995,  which provides a "safe harbor" for  forward-looking  statements to
encourage  companies  to  provide  prospective  information  so  long  as  those
statements  are  accompanied  by meaningful  cautionary  statements  identifying
important  factors that could cause  actual  results to differ  materially  from
those discussed in the statement.

     You  should   carefully   consider  the  following  risks.  The  risks  and
uncertainties  described below are not the only ones facing us. Additional risks
and  uncertainties  that are not presently known to us or that we currently deem
immaterial may also impair our business.

     If any of the events  described in the following risks actually occur,  our
business,  financial  condition  and results of  operations  could be materially
adversely  affected.  In such case, the trading prices of our common stock could
decline and you could lose all or part of your investment.

Our  current  debt is large and may  negatively  impact our  current  and future
financial stability.


     As of March 31, 2005, we had an aggregate of  approximately  $24,400,000 of
outstanding  indebtedness,  not including accounts payable, and accrued expenses
of approximately  $5,429,000.  As a result of our significant  indebtedness,  we
might not have the ability to incur any substantial additional indebtedness. The
level of our  indebtedness  could have several  important  effects on our future
operations, including:


     o    our  ability  to obtain  additional  financing  for  working  capital,
          acquisitions, capital expenditures and other purposes may be limited;

     o    a  significant  portion  of  our  cash  flow  from  operations  may be
          dedicated  to the  payment  of  principal  and  interest  on our debt,
          thereby reducing funds available for other purposes; and


                                       4


     o    our  significant  leverage  could make us more  vulnerable to economic
          downturns.

     If we are  unable to  service  our debt,  we will  likely be forced to take
remedial steps that are contrary to our business plan.


     As of March 31, 2005,  principal payments for our debt service requirements
on  a  monthly,  quarterly  and  annual  basis  were  $449,000,  $1,350,000  and
$5,399,000,  respectively.  It is possible  that our business  will not generate
sufficient cash flow from operations to meet our debt service  requirements  and
the payment of principal when due. If this were to occur, we may be forced to:


     o    sell assets at disadvantageous prices;

     o    obtain additional financing; or

     o    refinance  all or a portion of our  indebtedness  on terms that may be
          very unfavorable to us.

Our current bank loan contains  covenants that limit our operating and financial
flexibility and, if breached, could expose us to severe remedial provisions.

     Under the terms of our bank loan, we must:


     o    at the end of each month, have a current ratio of at least 1.4 to 1.0;

     o    at the end of each month, have a consolidated tangible net worth of at
          least $14,500,000;

     o    at the end of each  quarter,  have a ratio  of (a)  consolidated  cash
          flow, to (b) consolidated fixed charges of at least 1.25 to 1.0; and

     o    at the end of each  month,  not permit  our ratio of (a)  consolidated
          debt, to (b) consolidated tangible net worth to exceed 2.7 to 1.0.

        
     In addition to customary affirmative covenants, the loan agreement contains
various  restrictive   covenants  and  compliance   requirements.   Among  these
restrictions are limitations on our ability to:

     o    dispose of assets;

     o    incur additional indebtedness;

     o    create liens on our assets;

     o    repurchase, redeem or retire our capital stock or other securities;


                                       5


     o    merge or  consolidate,  or transfer  all or  substantially  all of our
          assets and the assets of our subsidiaries;

     o    engage in specified transactions with subsidiaries and affiliates;

     o    materially amend or modify our existing compressor leases;

     o    declare or pay dividends on our capital stock; and

     o    make any  significant  or  substantial  change  in the  nature  of our
          business as being conducted as of the date of the loan agreement.

     Our ability to meet the financial  ratios and tests under our bank loan can
be  affected  by events  beyond our  control,  and we may not be able to satisfy
those  ratios  and  tests.  A  breach  under  either  could  permit  the bank to
accelerate  the  debt so that it is  immediately  due and  payable.  No  further
borrowings  would be available under the credit  facility.  If we were unable to
repay the debt, the bank could proceed against our assets.


Approximately 69% of our compressor leases are leased for terms of six months or
less and, if terminated,  would adversely  impact our revenue and our ability to
recover our initial equipment costs.

     Approximately  69% of our  compressor  leases  are for  terms  of up to six
months.  There is a possibility that these leases could be terminated by lessees
within short  periods of time and that we may not be able to recover the cost of
a compressor for which a lease is terminated.


We must integrate the operations of acquired businesses.

     On January 3, 2005,  we  completed  our  acquisition  of Screw  Compression
Systems, Inc. ("SCS"). In connection with the acquisition, we nearly doubled our
long term debt and issued  609,576 of our shares of common  stock.  Our  success
will depend,  in part,  on our ability to integrate  the  operations  of SCS and
other  businesses  we  acquire in the  future,  including  centralizing  certain
functions to achieve cost savings,  pursuing programs and processes that promote
cooperation and the sharing of opportunities and resources, developing sales and
marketing  programs,  and retaining  acquired  customers.  We may not be able to
oversee the combined entity  efficiently or to implement  effectively our growth
and  operating  strategies.  To the extent that we  successfully  implement  our
acquisition  strategy,  our resulting growth will place  significant  additional
demands  on  our  management  and  infrastructure.   Our  failure  to  implement
successfully  our strategies or operate  effectively  the combined  entity could
have a material adverse effect on our business, financial condition, and results
of operations.  These effects could include lower revenue; higher cost of sales;
increased selling, general, and administrative expenses; and reduced margins.

The  anticipated  revenue  from the  affiliate  of Dominion  Michigan  cannot be
guaranteed.

     In connection  with our  acquisition of the  compression-related  assets of
Dominion Michigan,  an affiliate of Dominion Michigan committed until March 2006
to purchase  compressors  from us or enter into five year leases of  compressors
with us totaling  five-thousand  horsepower.  If, for any reason,  the affiliate


                                       6


does not fulfill this obligation to any material  extent,  our cash flow will be
significantly reduced and we may not be able to pay the principal or interest on
our debt as it becomes due.

We rely on two customers  for a significant  amount of our business and the loss
of these customers could  adversely  affect our operating  results and lower the
price of our common stock.


     Our business is dependent  not only on securing new  customers  but also on
maintaining  current  customers.  During the years ended December 2004 and 2003,
Dominion Exploration accounted for approximately 21% and 28% of our consolidated
revenue,  respectively.  For the three months  ended March  31,2005 our customer
XTO, obtained from the acquisition of SCS, represented 39% of total consolidated
revenue.  The loss of these two customers  could cause our operating  results to
fall  below  market  analysts'  expectations  and lower the price of our  common
stock.


We are dependent on a few suppliers for some of our  compressor  components  and
the loss of one of these suppliers could cause a delay in the  manufacturing  of
our compressors and reduce our revenue.


     We currently  obtain  approximately  20% of our compressor  components from
three  suppliers.  We  order  from  these  suppliers  as  needed  and we have no
long-term  contracts with either  supplier.  If either of these suppliers should
curtail its operations or be unable to meet our needs, we would encounter delays
in supplying our customers with compressors  until an alternative  supplier,  if
any, could be found. Such delays in our  manufacturing  process could reduce our
revenue and negatively impact our relationships with customers.


Decreased oil and gas industry  expenditure  levels would  adversely  affect our
revenue.

     Our revenue is derived from expenditures in the oil and gas industry, which
in turn,  are based on budgets to  explore  for,  develop  and  produce  oil and
natural  gas. If these  expenditures  decline,  our  revenue  will  suffer.  The
industry's willingness to explore,  develop and produce depends largely upon the
prevailing view of future oil and gas prices. Many factors affect the supply and
demand for oil and gas and, therefore, influence product prices including:

     o    the level of oil and gas production;

     o    the levels of oil and gas inventories;

     o    the expected cost of developing new reserves;

     o    the cost of producing oil and gas;

     o    the level of drilling activity;

     o    inclement weather;

     o    worldwide economic activity;

     o    regulatory  and other  federal  and state  requirements  in the United
          States;

     o    the ability of the  Organization of Petroleum  Exporting  Countries to
          set and maintain production levels and prices for oil;


                                       7


     o    terrorist activities in the United States and elsewhere;

     o    the cost of developing alternate energy sources;

     o    environmental regulation; and

     o    tax policies.

     If the demand for oil and gas  decreases,  then demand for our  compressors
     likely will decrease.

The intense competition in our industry could result in reduced profitability
and loss of market share for us.

     We sell or lease our products and sell our services in competitive markets.
In most of our business  segments,  we compete  with the oil and gas  industry's
largest  equipment and service  providers who have greater name recognition than
we do. These  companies also have  substantially  greater  financial  resources,
larger  operations and greater  budgets for marketing,  research and development
than we do.  They may be better  able to compete in making  equipment  available
quickly and more efficiently,  meeting delivery schedules or reducing prices. As
a result, we could lose customers and market share to those  competitors.  These
companies may also be better positioned than us successfully to endure downturns
in the oil and gas industry.

     Our operations may be adversely affected if our current  competitors or new
market entrants introduce new products or services with better prices, features,
performance or other competitive characteristics than our products and services.
Competitive  pressures  or other  factors also may result in  significant  price
competition that could harm our revenue and our business.

We might be unable to employ adequate  technical  personnel,  which could hamper
our plans for expansion or increase our costs.

     Many of the compressors  that we sell or lease are technically  complex and
often must perform in harsh conditions. We believe that our success depends upon
our ability to employ and retain a sufficient number of technical  personnel who
have the ability to design, utilize, enhance and maintain these compressors. Our
ability to expand our operations  depends in part on our ability to increase our
skilled  labor  force.  The  demand  for  skilled  workers is high and supply is
limited. A significant  increase in the wages paid by competing  employers could
result in a reduction of our skilled  labor  force,  or cause an increase in the
wage rates that we must pay, or both.  If either of these  events were to occur,
our cost structure could increase and our operations and growth  potential could
be impaired.

If we do not develop, produce and commercialize new competitive technologies and
products, our revenue may decline.

     The markets for natural gas compressor  products and services and for flare
systems, ignition systems and components for plant and production facilities are
characterized by continual technological developments.  As a result, substantial
improvements  in the scope and quality of product  function and  performance can
occur over a short  period of time.  If we are not able to develop  commercially
competitive  products in a timely  manner in response to changes in  technology,
our business and revenue may be adversely affected.


                                       8


     We may encounter  financial  constraints or technical or other difficulties
that could delay  introduction  of new products and services in the future.  Our
competitors  may introduce  new products  before we do and achieve a competitive
advantage.

     Additionally,  the time and expense invested in product development may not
result in commercial  applications that provide revenue. We could be required to
write off our entire  investment in a new product that does not reach commercial
viability.  Moreover,  we may experience operating losses after new products are
introduced  and  commercialized  because  of  high  start-up  costs,  unexpected
manufacturing costs or problems, or lack of demand.

We are subject to extensive environmental laws and regulations that could
require us to take costly compliance actions that could harm our financial
condition.

     Our manufacturing and maintenance  operations are significantly affected by
stringent and complex  federal,  state and local laws and regulations  governing
the  discharge of  substances  into the  environment  or  otherwise  relating to
environmental  protection. In these operations, we generate and manage hazardous
wastes such as solvents,  thinner,  waste paint, waste oil, washdown wastes, and
sandblast material.  We attempt to use generally accepted operating and disposal
practices and, with respect to acquisitions, will attempt to identify and assess
whether there is any environmental risk before completing an acquisition.  Based
on the nature of the industry,  however,  hydrocarbons  or other wastes may have
been disposed of or released on or under properties  owned,  leased, or operated
by us or on or under  other  locations  where  such  wastes  have been taken for
disposal.  The  wastes on these  properties  may be  subject to federal or state
environmental laws that could require us to remove the wastes or remediate sites
where they have been  released.  We could be exposed to  liability  for  cleanup
costs,  natural  resource  and other  damages as a result of our  conduct or the
conduct of, or  conditions  caused by, prior  operators or other third  parties.
Environmental laws and regulations have changed in the past, and they are likely
to change in the future.  If existing  regulatory  requirements  or  enforcement
policies change,  we may be required to make significant  unanticipated  capital
and operating expenditures.

Any failure by us to comply with applicable  environmental  laws and regulations
may result in governmental  authorities taking actions against our business that
could harm our operations and financial condition, including the:

     o    issuance of administrative, civil and criminal penalties;

     o    denial or revocation of permits or other authorizations;

     o    reduction or cessation in operations; and

     o    performance  of  site  investigatory,  remedial  or  other  corrective
          actions.


     We could be subject to  substantial  liability  claims  that could harm our
     financial condition.

     Our  products are used in hazardous  drilling and  production  applications
where an accident or a failure of a product can cause personal  injury,  loss of
life,  damage to  property,  equipment  or the  environment,  or  suspension  of
operations.


                                       9


     While we maintain insurance coverage, we face the following risks under our
insurance coverage:

     o    we may not be able to continue  to obtain  insurance  on  commercially
          reasonable terms;

     o    we may be faced with types of liabilities  that will not be covered by
          our insurance,  such as damages from significant  product  liabilities
          and from environmental contamination;

     o    the dollar amount of any liabilities may exceed our policy limits; and

     o    we do not maintain  coverage  against the risk of  interruption of our
          business.

     Any  claims  made  under our  policy  will  likely  cause our  premiums  to
increase.  Any future  damages  caused by our products or services  that are not
covered  by  insurance,  are in  excess  of  policy  limits  or are  subject  to
substantial  deductibles,  would reduce our earnings and our cash  available for
operations.

Liability to customers under  warranties may materially and adversely affect our
earnings.

     We  provide  warranties  as to the  proper  operation  and  conformance  to
specifications  of the  equipment we  manufacture.  Our equipment is complex and
often  deployed  in harsh  environments.  Failure of this  equipment  to operate
properly  or  to  meet  specifications  may  increase  our  costs  by  requiring
additional  engineering  resources  and  services,   replacement  of  parts  and
equipment or monetary  reimbursement to a customer. We have in the past received
warranty claims and we expect to continue to receive them in the future.  To the
extent that we incur substantial  warranty claims in any period, our reputation,
our ability to obtain future  business and our earnings  could be materially and
adversely affected.

Loss of key members of our management  could adversely affect our business while
we attempt to find their replacements.

     We depend  on the  continued  employment  and  performance  of  Wallace  C.
Sparkman,  our Chairman,  Stephen C. Taylor,  our  President,  Earl R. Wait, our
Treasurer and Chief Financial Officer,  and other key members of our management.
If any of our key managers  resigns or becomes unable to continue in his present
role and is not adequately replaced, our business operations could be materially
adversely  affected.  We do not maintain any "key man" life insurance for any of
our officers.

We must evaluate our intangible assets annually for impairment.

     Our intangible  assets are recorded at cost less  accumulated  amortization
and consist of goodwill and patent costs.  Through  December 31, 2001,  goodwill
was amortized using the straight-line method over 15 years and patent costs were
amortized over 13 to 15 years.

     In June 2001, the Financial  Accounting Standards Board issued Statement of
Financial  Accounting Standards No. 142, "Goodwill and Other Intangible Assets."
FAS 142 provides that: (1) goodwill and intangible  assets with indefinite lives
will no longer be amortized;  (2) goodwill and intangible assets with indefinite
lives must be tested for impairment at least annually;  and (3) the amortization
period for  intangible  assets  with  finite  lives will no longer be limited to
forty  years.  In the  event  that  we  determine  our  intangible  assets  with
indefinite lives have been impaired, we must record a write-down of those assets
on  our  statement  of  operations   during  the  period  of   impairment.   Our
determination of impairment will be based on various  factors,  including any of
the following factors, if they materialize:


                                       10


     o    significant  under  performance  relative  to expected  historical  or
          projected future operating results;

     o    significant changes in the manner of our use of the acquired assets or
          the strategy for our overall business;

     o    significant negative industry or economic trends;

     o    significant decline in our stock price for a sustained period; and

     o    our market capitalization relative to net book value.


     We adopted FAS 142 as of January 1, 2002.  Based on independent  valuations
in June 2003 and 2002 of our reporting units with goodwill,  adoption of FAS 142
has not had a material adverse effect on us through at least 2003. In the future
it could result in impairments of our intangible  assets or goodwill.  We expect
to continue to amortize  our  intangible  assets with finite lives over the same
time periods as previously  used,  and we will test our  intangible  assets with
indefinite  lives for  impairment at least once each year.  In addition,  we are
required to assess the consumptive life, or longevity,  of our intangible assets
with finite lives and adjust their amortization periods accordingly. As of March
31, 2005,  we had an aggregate of  approximately  $4,220,000  of net  intangible
assets.  We expect the carrying  value of net  intangible  assets could increase
significantly  if we acquire  additional  businesses.  Any  impairment in future
periods of those  assets,  or a  reduction  in their  consumptive  lives,  could
materially  and  adversely  affect our  statement of  operations  and  financial
position.


Provisions  contained in our  governing  documents  could hinder a change in our
control.

     Our  articles  of  incorporation  and bylaws  contain  provisions  that may
discourage acquisition bids and may limit the price investors are willing to pay
for our common  stock and  warrants.  Our articles of  incorporation  and bylaws
provide that:

     o    directors will be elected for  three-year  terms,  with  approximately
          one-third of the board of directors standing for election each year;

     o    cumulative voting is not allowed, which limits the ability of minority
          shareholders to elect any directors;

     o    the unanimous vote of the board of directors or the  affirmative  vote
          of the  holders of not less than 80% of the votes  entitled to be cast
          by the  holders  of all shares  entitled  to vote in the  election  of
          directors  is required  to change the size of the board of  directors;
          and

     o    directors  may only be  removed  for cause by holders of not less than
          80% of the votes entitled to be cast on the matter.

     Our board of directors has the authority to issue up to five million shares
of preferred  stock.  The board of directors  can fix the terms of the preferred
stock without any action on the part of our shareholders. The issuance of shares
of  preferred  stock may delay or  prevent a change in control  transaction.  In
addition,  preferred  stock  could  be used in  connection  with  the  board  of
director's  adoption  of a  shareholders'  rights  plan (also  known as a poison
pill),  which would make it much more difficult to effect a change in control of
us through  acquiring or  controlling  blocks of our stock.  Our  directors  and


                                       11


officers as a group  beneficially own stock.  Although this is not a majority of
our stock, it confers  substantial voting power in the election of directors and
management of us. This would make it difficult for other  minority  shareholders
to effect a change in control or otherwise  extend any significant  control over
our  management.  This may adversely  affect the market price and interfere with
the voting and other rights of our common stock.

You may suffer  substantial  dilution upon the exercise of outstanding  warrants
and options.


     As of March 31, 2005, we had  outstanding a significant  number of warrants
and options to purchase shares of our common stock. If these warrants or options
are exercised,  your percentage  ownership in Natural Gas Services Group will be
diluted and the price per share of our common stock may decline. We have

     o    issued  warrants to purchase up to 2,347,660  shares of common  stock;
          and

     o    granted options to purchase up to 130,500 shares of common stock.

Under our employee and director  stock  option  plans,  we may grant  options to
purchase  up to an  additional  19,500  shares  of  common  stock.  All  of  our
outstanding  warrants and options have exercise prices below $10.35, the closing
sale price of our common stock on May 18, 2005. Sales of substantial  amounts of
common  stock,  or a  perception  that such sales could occur,  could  adversely
affect the  market  price of the common  stock and could  impair our  ability to
raise capital through the sale of our equity securities.


If we issue  debt or  equity  securities,  you may lose  certain  rights  and be
diluted.

     If we raise  funds in the future  through  the  issuance  of debt or equity
securities, the securities issued may have rights and preferences and privileges
senior to those of holders of our common stock,  and the terms of the securities
may impose  restrictions  on our  operations or dilute your ownership in Natural
Gas Services Group.

We do not  intend  to pay,  and  have  restrictions  upon  our  ability  to pay,
dividends on our common stock.


     We have not paid  cash  dividends  in the  past  and do not  intend  to pay
dividends on our common  stock in the  foreseeable  future.  Net income from our
operations, if any, will be used for the development of our business,  including
capital  expenditures,  and to retire debt. In addition,  our bank loan facility
contains restrictions on our ability to pay cash dividends on our common stock.


We have a comparatively  low number of shares of common stock  outstanding  and,
therefore,  our common  stock may suffer from limited  liquidity  and its prices
will likely be volatile and its value may be adversely affected.

     Because of our relatively low number of outstanding shares of common stock,
the  trading  price of our common  stock will  likely be subject to  significant
price fluctuations and limited liquidity. This may adversely affect the value of
your  investment.  In  addition,  our  common  stock  price  could be subject to
fluctuations in response to variations in quarterly  operating results,  changes
in  management,  future  announcements  concerning  us,  general  trends  in the
industry and other events or factors as well as those described above.


The sale of stock by the selling shareholders may depress our stock price.


                                       12



     Under this prospectus,  the selling  shareholders may sell up to 701,171 of
their  shares  of our  common  stock,  representing  approximately  10.2% of our
outstanding common stock at the date of this prospectus. The sale of substantial
amounts of our stock owned by the selling  shareholders in the public market, or
the belief  that these  sales may occur,  could  reduce the market  price of our
stock,  making it more difficult for us to raise funds through future  offerings
of our common stock and to acquire businesses using our stock as consideration.



                           FORWARD LOOKING STATEMENTS

     Some statements contained in this prospectus,  any accompanying  prospectus
supplement,  and the documents  incorporated  by reference are  "forward-looking
statements"  within the meaning of Section 27A of the Securities Act of 1933 (or
Securities Act) and Section 21E of the Exchange Act. These  statements  include,
without limitation,  statements  relating to oil and gas prices,  demand for oil
and gas, budgets, business strategies and other plans, intentions and objectives
of our management  for future  operations and activities and other such matters.
The  words  "believe",   "budget",  "plan",  "estimate",   "expect",   "intend",
"strategy",  "project",  "will",  "could", "may",  "anticipate",  "continue" and
similar  expressions  identify  forward-looking   statements.   We  believe  the
assumptions and expectations  reflected in these forward-looking  statements are
reasonable.  However,  we cannot give any assurance that our  expectations  will
prove  to be  correct  or that we will be  able to take  any  actions  that  are
presently  planned.  Actual results could differ materially from those expressed
in the  forward-looking  statements.  Factors that could cause such a difference
include:

     o    fluctuations in prices of oil and gas;


     o    future capital requirements and availability of financing;

     o    competition;

     o    general economic conditions;

     o    governmental regulations;

     o    receipt of amounts owed to us by our customers;

     o    events similar to 911; and

     o    fluctuations in interest rates and availability of capital.

     You are cautioned not to place undue reliance on any of our forward-looking
statements,  which  speak only as of the date of the  document or in the case of
documents incorporated by reference, the date of those documents.





                                       13


                                 USE OF PROCEEDS


     We will not receive any  proceeds  from the sale of our common stock by the
selling shareholders. However, we will receive the proceeds, if exercised (other
than by cashless  exercise),  from warrants to purchase 582,203 shares of common
stock held by the selling shareholders.


               ISSUANCE OF SECURITIES TO THE SELLING SHAREHOLDERS

     The selling shareholders received the securities offered in this prospectus
pursuant to the following transactions.

     In early 2001,  in a private  placement  we issued  units  comprised of 10%
Subordinated  Notes and Warrants to purchase up to 616,175  shares of our common
shock to the selling shareholders.  The warrants issued in the private placement
have a term of five years and are  exercisable at $3.25 per share.  The warrants
can be  exercised by paying cash,  or by way of  "cashless  exercise"  whereby a
portion of the shares  underlying the warrant are used, at the fair market value
of our common stock on the date of exercise,  to pay the exercise  price for the
remaining shares underlying the warrant.

     In March 2001, we issued  warrants to purchase  68,524 shares of our common
stock at $2.50 per share in  exchange  for  persons  guaranteeing  approximately
$1,749,000 of our debt.  The warrants can be exercised by paying cash, or by way
of "cashless  exercise"  whereby a portion of the shares  underlying the warrant
are used,  at the fair market value of our common stock on the date of exercise,
to pay the exercise price for the remaining shares  underlying the warrant.  The
warrants  expire on December  31,  2006,  and they were issued to the  following
persons for guaranteeing the amount of our debt indicated:

                                     Number of Shares              Amount of
     Name                           Underlying Warrants         Debt Guaranteed
     ----                           -------------------         ---------------
     Wallace O. Sellers                   21,936                  $548,399
     Wallace C. Sparkman(1)               21,467                   536,671
     CAV-RDV, Ltd.(2)                     15,756                   393,902
     Richard L. Yadon                      9,365                   234,121
---------------------------

(1)  Wallace C. Sparkman is our Chairman of the Board. Mr. Sparkman subsequently
     transferred  his  warrants  for 21,467  shares to Diamond S DGT, a trust of
     which  Scott W.  Sparkman  is the  trustee  and a  beneficiary.  Wallace C.
     Sparkman  has  represented  to us that  he has no  beneficial  interest  in
     Diamond S DGT.

(2)  CAV-RDV,  Ltd.,  is a Texas  limited  partnership  for the  benefit  of the
     children of Wayne L. Vinson, our former Chief Executive Officer.

     In April 2002, we issued  warrants to purchase  16,472 shares of our common
stock  at  $3.25  per  share  in  exchange   for  three   persons   guaranteeing
approximately  $824,000 of our debt.  The  warrants  can be  exercised by paying
cash,  or by way  of  "cashless  exercise"  whereby  a  portion  of  the  shares
underlying the warrant are used, at the fair market value of our common stock on
the  date of  exercise,  to pay the  exercise  price  for the  remaining  shares
underlying the warrant.  The warrants expire on December 31, 2007, and they were
issued  to the  following  persons  for  guaranteeing  the  amount  of our  debt
indicated:



                                       14



                                     Number of Shares      Amount of Additional
     Name                           Underlying Warrants      Debt Guaranteed
     ----                           -------------------    --------------------
     Wallace O. Sellers(1)                 9,032               $  451,601
     CAV-RDV, Ltd.(2)                      2,122                  106,098
     Richard L. Yadon(1)                   5,318                  265,879
---------------------------

(1)  Messrs. Sellers and Yadon serve as directors on our Board of Directors.

(2)  CAV-RDV,  Ltd.,  is a Texas  limited  partnership  for the  benefit  of the
     children of Wayne L. Vinson, our former Chief Executive Officer.


     We will not receive any proceeds in  connection  with the sale of shares by
the selling  shareholders  listed below;  however, we will receive proceeds from
any cash exercise of the warrants.

     Although not required to do so, we have filed a registration  statement, to
which this prospectus forms a part, in order to permit the selling  shareholders
to resell to the  public the  shares of common  stock they have or may  acquired
pursuant to the exercise of the warrants.

     We will pay all expenses of  registering  the shares  under the  Securities
Act,  including all registration,  listing and filing fees,  printing  expenses,
fees and  disbursements of our counsel,  expenses of any special audits incident
to or  required  by  the  registration,  and  expenses  of  complying  with  the
securities or blue sky laws of any jurisdictions.  The selling shareholders will
pay all discounts,  brokerage fees, commissions and expenses for any shares that
are registered and that they sell.













                                       15




                              SELLING SHAREHOLDERS

     The  following  table  sets  forth  information  provided  by  the  selling
shareholders about the ownership of our common stock by the selling shareholders
before and after the offering covered by this prospectus.


                                                   Shares                                Shares             Percentage of Shares
                                                Beneficially       Shares Being       Beneficially           Beneficially Owned
                                                  Owned             Offered in           Owned
                                                  Before               The               After            Before         After
Name                                             Offering(1)        Offering(2)        Offering(2)        Offering       Offering
----                                            ------------       ------------       ------------        --------       --------
                                                                                                          
Robert A. Street                                      10,000             10,000                -0-        *              *
William E. Beggs                                      10,000             10,000                -0-        *              *
Gary W. and Theresa L. Boening                        24,400             20,000              4,400        *              *
Alvin R. Bonnette Revocable Trust(3)                  75,900             68,000              7,900        1.1            *
The Burns Partnership(4)                             176,000             10,000            166,000        2.6            2.4
Butera Family Trust(5)                                58,000             24,000             34,000        *              *
Joseph E. Carothers                                   29,172             18,000             11,172        *              *
CAV-RDV, Ltd.(6)                                     177,878             17,878            160,000        2.6            2.4
Charles Curtis                                        78,000             40,000             38,000        1.7            *
Leslie W. David Trust(7)                              11,600             10,000              1,600        *              *
Loretta J. David-Roth IRA                             11,600             10,000              1,600        *              *
Diamond S. DGT(8)                                    496,467             21,467            475,000        7.3            7.0
Robert C. Dixon/IRA                                   37,900             10,000             27,900        *              *
Alvin J. Donius                                       10,000             10,000                -0-        *              *
Zenas N. Gurley                                      166,471             10,471            156,000        2.5            2.3
William F. Hughes(9)                                 247,000             60,000            187,000        3.6            2.7
Roy A. Johnson Revocable Trust(10)                    12,000             10,000              2,000        *              *
Albert W. Karnath                                     26,800             10,000             16,800        *              *
John Karnath                                          10,000             10,000                -0-        *              *
Lorie Karnath                                         10,000             10,000                -0-        *              *
Paul M.Karnath                                        10,000             10,000                -0-        *              *
Alan Kurus                                            33,704             31,704              2,000        *              *
Elise L. Lyon Revocable Living Trust                  10,000             10,000                -0-        *              *
Utd. 9/23/96(11)                                                                                         
Sally Jo Maisano                                      36,000             26,000             10,000        *              *
Darell&Thordis Norris Trust(12)                       16,000             10,000              6,000        *              *
Mary Jane Peck                                        26,800             20,000              6,800        *              *
B. Kay Phillips                                       10,000             10,000                -0-        *              *
Sharon L. Pitken-IRA                                 112,000             36,000             76,000        1.6            1.1
G Five Development LLC(13)                            82,000             32,000             50,000        1.2            *
Earl W. Sauder Trust(14)                              32,408             20,000             12,408        *              *
David C. Shatzer                                      55,200             20,000             35,200        *              *
Gary E. Schenkel                                      11,000             10,000              1,000        *              *
Wallace O. Sellers(15)                               693,159             30,968            662,191        10.2           9.8
Donald L. Smallwood                                   10,000             10,000                -0-        *              *
Kipp/Glenda Jo Smallwood                              10,000             10,000                -0-        *              *
Lazaros/Patricia Voreadis                             30,000             10,000             20,000        *              *
Richard L. Yadon(16)                                 299,183             14,683            284,500        4.4            4.2
                                                ------------       ------------       ------------                            
TOTALS                                             3,156,642            701,171          2,455,471       

* Less than 1%
-----------------



                                       16



(1)  Beneficial  ownership  is  determined  in  accordance  with  Rule  13d-3(d)
promulgated by the SEC under the Exchange Act, which includes shares  underlying
the  warrants and any other  securities  which are  convertible  into our common
stock within 60 days of the date of this  prospectus.  The  calculations  of the
percentages of shares  beneficially owned are based upon 6,782,764 shares of our
common  stock  outstanding  at March 31,  2005 and  assume the  exercise  of the
warrants  (which are  exercisable  for shares of our common  stock) held by that
selling shareholder.

(2)  The selling  shareholders  may offer shares under this prospectus from time
to time and may elect to sell none,  some or all of the shares set forth  above.
As a result,  we cannot  estimate  the number of shares of our common stock that
the selling  shareholders will beneficially own after termination of sales under
this prospectus.  For purposes of this table,  however, we have assumed that the
selling shareholders sell all of their shares issued or issuable pursuant to the
warrants.  In addition,  the selling shareholders may have sold,  transferred or
otherwise disposed of all or a portion of their shares of our common stock since
the date on which they provided information for this table.

(3)  Alvin R. Bonnette is the Trustee of the Alvin R. Bonnette  Revocable  Trust
and consequently has voting and investment control over the shares.  Each of Mr.
Bonnette's six children are beneficiaries under the trust.

(4)  William Burns, David Burns, Michael Burns, Barbara Burns, and Jeffrey Burns
are the  members  and  beneficial  owners  of The Burns  Partnership,  a general
partnership, and each such person consequently has voting and investment control
over the shares.

(5)  Roy T. Butera is trustee of the Butera  Family Trust and  consequently  has
voting and  investment  control  over the  shares.  Each of Mr.  Butera's  three
children are beneficiaries under the trust.

(6)  The children of Wayne L. Vinson,  our former Chief Executive  Officer,  are
the beneficial owners of CAV-RDV, Ltd., at Texas Limited Partnership. 

(7)  Leslie W. David is trustee  of the Leslie W. David  Trust and  consequently
has voting and investment  control over the shares.  Mr.  David's wife,  Loretta
David, is the beneficiary under the trust.

(8)  The  warrant for 21,467  shares of our common  stock at $6.25 per share was
initially issued to Wallace C. Sparkman, our Chairman of the Board. Mr. Sparkman
subsequently  transferred  his warrants  for 21,467  shares to Diamond S. DGT, a
trust of which Scott W.  Sparkman is the trustee and a  beneficiary.  Wallace C.
Sparkman has represented to us that he has no beneficial  interest in Diamond S.
DGT.

(9)  The  247,000  beneficially  owned  shares  include (i) 1,500  shares  owned
directly by William F. Hughes,  Jr., (ii) 180,500  shares held by the William F.
and  Cheryl C.  Hughes  Family  Trust in which  William  and  Cheryl  Hughes are
co-trustees  and  consequently  share  voting and  investment  over the  shares;
William  and Cheryl  Hughes are also  beneficiaries  under the trust  along with
their two  children,  and (iii) 5,000  shares  issuable  upon  exercise of stock
options ranging from $5.55 to $9.34 per share,  held by William F. Hughes,  Jr.,
and (iv) the 60,000 shares registered herein which are issuable upon exercise of
a stock warrant at $3.25 per share, held by William F. Hughes, Jr.

(10) Roy A.  Johnson  is  trustee  of the Roy A.  Johnson  Revocable  Trust  and
consequently  has voting and  investment  control  over the shares.  Each of Mr.
Johnson's two children are beneficiaries  under the trust. 

(11) Elise S. Lyon is trustee of the Elise S. Lyon  Revocable  Living  Trust Utd
9/23/96 and consequently has voting and investment control over the shares. Each
of Ms. Lyon's three children are beneficiaries under the trust.

(12) Darell Norris and Thordis Norris are co-trustees and  beneficiaries  of the
Darell & Thordis  Norris  Trust and  consequently  share  voting and  investment
control over the shares.

(13) Roland  W.  Gentner,  a  resident  of  Rapid  City,  South  Dakota,  is the
beneficial  owner of G Five  Development  LLC, a South Dakota limited  liability
company. Mr. Gentner beneficially owns 369,000 shares of our common stock.

(14) Earl W. Sauder is trustee of the Earl W. Sauder Trust and  consequently has
voting and investment control over the shares.  Mr. Sauder's wife,  children and
grandchildren are beneficiaries.
 
(15) Wallace O. Sellers is a Director of our Company.  The 693,159  beneficially
owned shares  include (i) 134,877  shares owned  directly by Wallace O. Sellers,
(ii) 158,600 shares owned through Mr. Sellers' wife, (iii) 7,500 shares issuable
upon  exercise  of stock  options  ranging  from $3.88 to $9.34 per share,  (iv)
196,091  shares  held  in a trust  in  which  Mr.  Sellers'  wife is a  lifetime
beneficiary  and an unrelated  third party acts as trustee,  (v) 196,091  shares
held in a trust in which Mr. Sellers' wife is a contingent  beneficiary,  and an
unrelated third party acts as trustee.  Mr. Sellers  disclaims  ownership of all
shares held in the two trusts.

(16) Richard L. Yadon is a Director of our  Company.  The  299,193  beneficially
owned shares include (i) 279,500 shares owned directly by Richard L. Yadon, (ii)
5,000 shares issuable upon exercise of stock options ranging from $5.55 to $9.34
per share,  and (iii) 14,683 shares  issuable upon exercise of stock warrants at
$2.50 and $3.25 per share.


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


                              PLAN OF DISTRIBUTION

     The shares of common stock  covered by this  prospectus  may be offered and
sold  from  time  to  time  by  the  selling  shareholders.  The  term  "selling
shareholders"    includes    donees,    pledgees,     transferees    or    other
successors-in-interest selling shares received after the date of this prospectus
from a selling shareholder as a gift, pledge,  shareholder distribution or other
non-sale related transfer. The selling shareholders will act independently of us
in making decisions with respect to the timing, manner and size of each sale.


                                       17


     Sales of shares by the selling shareholders  referred to in this prospectus
may be made from time to time in one or more  transactions on the American Stock
Exchange,  in the  over-the-counter  market or any other  exchange or  quotation
system  on which  shares  of our  common  stock  may be  listed  or  quoted,  in
negotiated  transactions or in a combination of any such methods of sale.  Sales
may be at fixed prices that may be changed,  at market prices  prevailing at the
time  of  sale,  at  prices  related  to such  prevailing  market  prices  or at
negotiated  prices.  The shares may be offered  directly to  purchasers or to or
through  underwriters  or agents  designated  from time to time or to or through
brokers or dealers, or through any combination of these methods of sale.

     The methods by which the shares may be sold include:

     o    block trades (which may involve crosses) in which the broker or dealer
          will  attempt to sell the  securities  as agent but may  position  and
          resell  a  portion  of  the  block  as  principal  to  facilitate  the
          transaction;

     o    purchases by a broker or dealer as principal  and resale by the broker
          or dealer for its own account under this prospectus;

     o    exchange  distributions or secondary  distributions in accordance with
          the rules of the American Stock Exchange or other relevant markets;

     o    short sales, ordinary brokerage transactions and transactions in which
          the broker solicits purchasers;

     o    transactions  in  options,   swaps  or  other   derivatives,   whether
          exchange-listed or otherwise;

     o    firm commitment or best efforts underwritings; and

     o    privately negotiated transactions.

     In addition,  sales not covered by this  prospectus may also be made by the
selling  shareholders under Rule 144 or another  applicable  exemption under the
Securities Act.

     From time to time the selling  shareholders may distribute a portion or all
of their shares to their owners. In the event of such a distribution, and to the
extent these owners intend to use this prospectus to sell any of such shares, if
required  these owners will be  identified  in a supplement  to this  prospectus
filed with the SEC.  Furthermore,  to the extent required,  this prospectus also
may be amended or supplemented  from time to time to describe a specific plan of
distribution or any material  arrangement that a selling shareholder has entered
into  for  the  sale  of  shares,  including  the  details  of any  underwritten
distribution.

     In  connection  with  distributions  of shares or  otherwise,  the  selling
shareholders may enter into hedging  transactions  with  broker-dealers or other
agents.  In connection with these  transactions,  broker-dealers or other agents
may engage in short sales of shares in the course of hedging the positions  they
assume with the selling  shareholders.  The selling  shareholders  may also sell
shares short and  redeliver the shares to close out their short  positions.  The
selling  shareholders  may also enter  into  option or other  transactions  with
broker-dealers or other financial institutions that require the delivery to that
broker-dealer  or  other  financial   institution  of  shares  offered  by  this
prospectus,  which shares that broker-dealer or other financial  institution may


                                       18


resell  under this  prospectus  (as  supplemented  or  amended  to  reflect  the
transaction).  The  selling  shareholders  may also  pledge or grant a  security
interest  in  shares  and,  upon a default  in the  performance  of the  secured
obligation,  the pledgee or secured party may affect sales of the pledged shares
under this prospectus (as supplemented or amended to reflect the transaction).

     In  effecting  sales,  broker-dealers  or  agents  engaged  by the  selling
shareholders   may   arrange   for   other    broker-dealers   to   participate.
Broker-dealers,  underwriters  or agents may receive  commissions,  discounts or
concessions from the selling  shareholders  and/or  purchasers of the shares for
whom they may act as agents.

     In offering the shares covered by this prospectus, the selling shareholders
and any broker-dealers, underwriters or agents who execute sales for the selling
shareholders  may be deemed  to be  "underwriters"  within  the  meaning  of the
Securities  Act in  connection  with these  sales.  Any profits  realized by the
selling  shareholders and the compensation of any broker-dealer,  underwriter or
agent  may  be  deemed  to  be  underwriting   discounts  and  commissions.   No
underwriter,  broker-dealer  or agent has been engaged by us in connection  with
the distribution of the shares.

     To comply with the securities  laws of certain states,  if applicable,  the
shares must be sold in those  jurisdictions  only through registered or licensed
brokers or dealers.  In addition,  in certain  states the shares may not be sold
unless they have been  registered or qualified for sale in the applicable  state
or an exemption from the registration or qualification  requirement is available
and is complied with.

     The  selling   shareholders  and  any  other  person   participating  in  a
distribution  of the shares  covered by this  prospectus  will be subject to the
applicable  provisions  of the  Exchange  Act  and  the  rules  and  regulations
thereunder.  Regulation  M of the Exchange Act may limit the timing of purchases
and  sales of shares  by the  selling  shareholders  and any  other  person.  In
addition,  Regulation M may  restrict  the ability of any person  engaged in the
distribution of the shares to engage in market-making activities with respect to
our  common  stock  for  a  period  of up  to  five  business  days  before  the
distribution.


                                  LEGAL MATTERS

     The validity under Colorado law of the shares will be passed upon for us by
Jackson Kelly PLLC, Denver, Colorado.


                                     EXPERTS


     HEIN & ASSOCIATES LLP, independent  registered public accounting firm, have
audited  our   consolidated   balance  sheet  at  December  31,  2004,  and  the
consolidated statements of income,  shareholders' equity and cash flows for each
of the two years ended December 31, 2004 and 2003, as set forth in their report,
which  is  incorporated  in  this  prospectus  by  reference.  Our  consolidated
financial  statements are incorporated by reference in reliance on their report,
given on their authority as experts in accounting and auditing.



                                       19


          We  have  not  authorized  any
dealer,  salesperson  or other person to
give  any  information  or to  make  any
representation  not  contained  in  this
prospectus.  This  prospectus  does  not
constitute   an  offer  to  sell,  or  a
solicitation  of an  offer  to buy,  any
offer or  solicitation  by anyone in any
jurisdiction not authorized, or in which
the  person  making  such  an  offer  or
solicitation  is not  qualified to do so
or to any person to whom it is  unlawful
to make  such an offer or  solicitation.
By delivery of this prospectus we do not
imply  that  there has been no change in
our affairs or that the  information  in
this  prospectus  is  correct  as of any
time subsequent to its date.

                                                            NATURAL GAS SERVICES
           TABLE OF CONTENTS                                GROUP, INC.


                                                          Page


Where You Can Find Additional Information                   2
Incorporation of Documents by Reference                     2
About Natural Gas Services Group, Inc.                      3                   
                                                                      ----------
Risk Factors                                                4

Forward Looking Statements                                 13         PROSPECTUS
Use of Proceeds                                            14                   
                                                                      ----------
Issuance of Securities to the Selling Shareholders         14
Selling Shareholders                                       16
Plan of Distribution                                       17
Legal Matters                                              19
Experts                                                    19





                                                                    May __, 2005





                                       20


                                     PART II


                     INFORMATION NOT REQUIRED IN PROSPECTUS


Item 14. Other Expenses of Issuance and Distribution.

     Expenses  payable by us in connection with the issuance and distribution of
the securities being registered hereby are as follows:


     Securities and Exchange Commission registration fee       $         855
     Accounting fees and expenses                              $       2,000
              Legal fees and expenses                          $       7,500
              Printing expenses                                $       1,000
     Transfer agent fees                                       $         500
              Miscellaneous                                    $         145
                                                               -------------

       Total                                                   $      12,000    
                                                               =============


     All of the above expenses except for the Securities and Exchange Commission
registration  fee are  estimated.  All such items  will be borne by Natural  Gas
Services Group, Inc.

Item 15.  Indemnification of Directors and Officers.

     Section  7-109-102  of the  Colorado  Business  Corporation  Act  permits a
Colorado  corporation to indemnify any director against liability if such person
acted in good faith and, in the case of conduct in an official capacity with the
corporation, that the director's conduct was in the corporation's best interests
and, in all other cases, that the director's conduct was at least not opposed to
the best interests of the corporation  or, with regard to criminal  proceedings,
the  director  had no  reasonable  cause to believe the  director's  conduct was
unlawful.

     Section 7-109-103 of the Colorado  Business  Corporation Act provides that,
unless limited by its articles of  incorporation,  a Colorado  corporation shall
indemnify a person who was wholly successful, on the merits or otherwise, in the
defense of any  proceeding to which the person was a party because the person is
or  was a  director,  against  reasonable  expenses  incurred  by  him or her in
connection with the proceeding.

     Section 3 of Article IX of our articles of  incorporation  provides that we
shall  indemnify,  to the maximum extent permitted by law in effect from time to
time, any person who is or was a director, officer, agent, fiduciary or employee
of ours against any claim,  liability or expense  arising against or incurred by
such person made party to a proceeding because such person is or was a director,
officer,  agent,  fiduciary or employee of ours or because such person is or was
serving  another  entity as a director,  officer,  partner,  trustee,  employee,
fiduciary or agent at our request.  We further have the authority to the maximum
extent  permitted  by law to purchase  and  maintain  insurance  providing  such
indemnification.

     Article  VI of our  bylaws  provides  for the  indemnification  of  certain
persons.

     Insofar as indemnification for liabilities arising under the Securities Act
of 1933 may be permitted to our  directors,  officers  and  controlling  persons
pursuant to the foregoing provisions, or otherwise, we have been advised that in
the opinion of the Securities and Exchange  Commission such  indemnification  is
against  public  policy  as  expressed  in the  Securities  Act of 1933  and is,
therefore, unenforceable.


                                      II-1


Item 16. Exhibits.

     The following is a list of all exhibits filed as part of this  Registration
Statement:

Exhibit
  No.                             Description
-------                           -----------
 5             Legal Opinion of Jackson Kelly PLLC*

 10.5          Form of Five-Year Warrants to Purchase Common Stock (1)

 23.1          Consent of Jackson Kelly PLLC (Included in Exhibit 5)

 23.2          Consent of HEIN & ASSOCIATES LLP*


 24            Power of Attorney (see the signature page)(2)

                           
*Filed herewith

(1)  Incorporated by reference to the Company's  Registration  Statement on Form
SB-2 (No. 333-88314)


(2)  Previously filed


Item 17.  Undertakings.

The undersigned Registrant hereby undertakes:

     (1)  to file,  during any period in which offers or sales are being made, a
          post-effective amendment to this Registration Statement.

          (i)  To include any  prospectus  required  by Section  10(a)(3) of the
               Securities Act of 1933, as amended;

          (ii) To reflect in the  prospectus  any facts or events  arising after
               the effective  date of this  Registration  Statement (or the most
               recent post-effective  amendment thereof) which,  individually or
               in  the  aggregate,   represent  a  fundamental   change  in  the
               information   set   forth   in   this   Registration   Statement.
               Notwithstanding the foregoing, any increase or decrease in volume
               of  securities  offered (if the total dollar value of  securities
               offered  would not  exceed  that  which was  registered)  and any
               deviation  from  the low or  high  end of the  estimated  maximum
               offering  range may be reflected in the form of prospectus  filed
               with the  Securities  and  Exchange  Commission  pursuant to Rule
               424(b)  if, in the  aggregate,  the  changes  in volume and price
               represent  no more  than a 20%  change in the  maximum  aggregate
               offering price set forth in the "Calculation of Registration Fee"
               table in the effective registration statement; and

          (iii)To include any material  information  with respect to the plan of
               distribution  not  previously   disclosed  in  this  Registration
               Statement  or any  material  change to such  information  in this
               Registration Statement. Provided, however, that paragraphs (1)(i)


                                      II-2


               and  (1)(ii)  do not  apply  if the  information  required  to be
               included in a  post-effective  amendment by those  paragraphs  is
               contained  in periodic  reports  filed with or  furnished  to the
               Securities and Exchange  Commission by the Registrant pursuant to
               Section 13 or Section  15(d) of the  Securities  Exchange  Act of
               1934,  as amended,  that are  incorporated  by  reference in this
               Registration Statement.

     (2)  That,  for  the  purpose  of  determining   any  liability  under  the
          Securities Act, each such post-effective  amendment shall be deemed to
          be a new  registration  statement  relating to the securities  offered
          herein,  and the  offering  of such  securities  at that time shall be
          deemed to be the initial bona fide offering thereof.

     (3)  To remove from registration by means of a post-effective amendment any
          of  the  securities  being  registered  which  remain  unsold  at  the
          termination of the offering.

     The  undersigned   Registrant  hereby  undertakes  that,  for  purposes  of
determining  any  liability  under  the  Securities  Act,  each  filing  of  the
Registrant's  Annual  Report  pursuant to Section  13(a) or Section 15(d) of the
Exchange Act (and, where  applicable,  each filing of an employee benefit plan's
annual  report   pursuant  to  Section  15(d)  of  the  Exchange  Act)  that  is
incorporated by reference in this Registration Statement shall be deemed to be a
new registration  statement relating to the securities offered therein,  and the
offering of such  securities at that time shall be deemed to be the initial bona
fide offering thereof.

     Insofar as indemnification for liabilities arising under the Securities Act
of 1933 may be permitted to directors,  officers and controlling  persons of the
Registrant pursuant to the provisions  described in Item 15 above, or otherwise,
the  Registrant  has been  advised  that in the  opinion of the  Securities  and
Exchange  Commission such  indemnification is against public policy as expressed
in the  Securities  Act and is,  therefore,  unenforceable.  In the event that a
claim for  indemnification  against such liabilities  (other than the payment by
the  Registrant  of  expenses  incurred  or  paid  by  a  director,  officer  or
controlling  person of the Registrant in the  successful  defense of any action,
suit or proceeding) is asserted by such director,  officer or controlling person
in connection with the securities being registered,  the Registrant will, unless
in the  opinion  of its  counsel  the matter  has been  settled  by  controlling
precedent,  submit to a court of appropriate  jurisdiction  the question whether
such  indemnification  by it is  against  public  policy  as  expressed  in  the
Securities Act and will be governed by the final adjudication of such issue.





                                      II-3


                                   SIGNATURES

     In accordance  with the  requirements  of the  Securities  Act of 1933, the
registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements of filing on Form S-3 and has duly caused this Amendment No.
1 to this registration  statement to be signed on its behalf by the undersigned,
thereunto  duly  authorized,  in the City of Midland,  State of Texas on May 23,
2005.

                                      NATURAL GAS SERVICES GROUP, INC.


                                       /s/ Stephen C. Taylor                    
                                      ------------------------------------------
                                      Stephen C. Taylor, President and Principal
                                      Executive Officer


                                       /s/ Earl R. Wait                         
                                      ------------------------------------------
                                      Earl R. Wait, Principal Financial and
                                      Accounting Officer



     Pursuant  to  the   requirements  of  the  Securities  Act  of  1933,  this
registration statement was signed by the following persons in the capacities and
on the dates indicated:


       Signature                              Title                     Date
       ---------                              -----                     ----

/s/ EARL R. WAIT                       Director (Chairman)          May 23, 2005
---------------------------                                                    
Attorney-in-fact for
Wallace C. Sparkman


/s/ EARL R. WAIT                       Director                     May 23, 2005
---------------------------                                                     
Attorney-in-fact for
Wallace O. Sellers


/s/EARL R. WAIT                        Director                     May 23, 2005
---------------------------                                                     
Attorney-in-fact for
Charles G. Curtis


/s/ EARL R. WAIT                       Director                     May 23, 2005
---------------------------                                                     
Attorney-in-fact for
William F. Hughes


/s/ EARL R. WAIT                       Director                     May 23, 2005
---------------------------                                                     
Attorney-in-fact for
Gene A. Strasheim


/s/ EARL R. WAIT                       Director                     May 23, 2005
---------------------------                                                    
Attorney-in-fact for
Richard L. Yadon


/s/ EARL R. WAIT                       Director                     May 23, 2005
---------------------------                                                    
Attorney-in-fact for
Paul Hensley



                                      II-4


                                  EXHIBIT INDEX



Exhibit
  No.                             Description
-------                           -----------

 5            Legal Opinion of Jackson Kelly PLLC*

 10.5         Form of Five-Year Warrants to Purchase Common Stock (1)

 23.1         Consent of Jackson Kelly PLLC (Included in Exhibit 5)

 23.2         Consent of HEIN & ASSOCIATES LLP*


 24           Power of Attorney (see the signature page) (2)

                           
*Filed herewith

(1)  Incorporated by reference to the Company's  Registration  Statement on Form
SB-2 (No. 333-88314)


(2)  Previously filed