EXHIBIT 5.1

                       [DORSEY & WHITNEY LLP LETTERHEAD]


                                  July 16, 2002

Natural Gas Services Group, Inc.
2911 SCR 1260
Midland, TX  78706

Ladies and Gentlemen:

         Natural Gas Services Group, Inc. ("Natural Gas") has requested our
opinion as to certain matters that relate to the issuance of the shares of $0.01
par value common stock ("Common Stock") and warrants to purchase Common Stock
("Warrants") which are described on the cover page of Registration Statement No.
333-88314 Natural Gas has filed with the United States Securities and Exchange
Commission.

         We have reviewed the Articles of Incorporation, as amended, of Natural
Gas, the minutes of the board of directors and of the shareholders of Natural
Gas and such other documents that we considered necessary in order to render
this opinion. In conducting such review, we have assumed (i) that all signatures
are genuine, (ii) that all documents and instruments submitted to us as copies
conform with the originals, and (iii) the due execution and delivery of all
documents where due execution and delivery are a prerequisite to the
effectiveness thereof. As to any facts material to this opinion, we have relied
upon statements and representations of officers and other representatives of
Natural Gas and certificates of public officials and have not independently
verified such facts.

         Based solely on the foregoing, we are of the opinion that the shares of
Common Stock and Warrants are validly authorized, and assuming the shares of
Common Stock and Warrants are paid for as described in such Registration
Statement, when issued, the shares of Common Stock and Warrants will be validly
issued, fully paid and nonassessable.

         This opinion is limited to the applicability of the Colorado Business
Corporation Act and the common law of Colorado to the issuance of the shares of
Common Stock and Warrants. This opinion does not cover or in any way relate to
the applicability of, or compliance by Natural Gas with, any other law,
including any federal or state securities laws, the statutory or common law of
any other state or any other federal law.






                              DORSEY & WHITNEY LLP



Natural Gas Services Group, Inc.
July 16, 2002
Page 2


         We consent to the filing of this opinion as an exhibit to the
Registration Statement of Natural Gas and to Natural Gas describing this firm as
having issued this opinion in the Prospectus that is a part of the Registration
Statement.

                                             Sincerely yours,


                                             /s/ Dorsey & Whitney LLP