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                                                                     EXHIBIT 5.1


                                      
                               Vinson & Elkins
                               Attorneys At Law
                            Vinson & Elkins L.L.P.
                          3700 Trammell Crow Center
                               2001 Ross Avenue
                           Dallas, Texas 75201-2975
                           Telephone (214) 220-7700
                              Fax (214) 220-7716



                                   May 7, 1997

Mewbourne Development Corporation
3901 S. Broadway
Tyler, TX  75701

         Re:      Mewbourne Energy 98 Drilling Program

Gentlemen:

         We have acted as counsel to Mewbourne Development Corporation, a
Delaware corporation ("MD"), in connection with the registration under the
Securities Act of 1933, as amended (the "Act"), of a maximum of 2,000 limited
partner interests and a maximum of 8,000 general partner interests
(collectively, the "Interests") in a limited partnership (the "Partnership")
formed by MD pursuant to the Delaware Revised Uniform Limited Partnership Act
(the "Delaware Act") and of which MD serves as the Managing Partner. The
Partnership is named Mewbourne Energy Partners 98-A, L.P. A registration
statement on Form S-1 (Registration No. 333-46843) has been filed under the Act
and the Rules and Regulations of the Securities and Exchange Commission (the
"Commission") promulgated thereunder with respect to the offering of the
Interests (as so amended, the "Registration Statement"), but has not yet become
effective under the Act.

         In reaching the opinion set forth herein, this firm has reviewed (a)
the Certificate of Incorporation, Bylaws, and records of proceedings of the
Board of Directors of MD, (b) the form of Agreement of Partnership ("Partnership
Agreement") for the Partnership that is included as Exhibit A to the Prospectus
forming a part of the Registration Statement, and (c) except as set forth below,
such other agreements, certificates of public officials, certificates of
officers of MD, records, documents, and matters of law that this firm deemed
relevant. As to various questions of fact material to this opinion, where
relevant facts were not independently established, we have relied upon
statements of officers of MD.

         Based on and subject to the foregoing and subject further to the
assumptions, exceptions, and qualifications hereinafter stated, it is the
opinion of this firm that when the Interests in the Partnership are sold to the
subscribers and the subscribers are admitted as general partners or limited
partners, as the case may be, to the Partnership, subject to compliance with
federal and state securities laws (as to which this firm expresses no opinion)
such Interests will be legally issued and, 


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Securities and Exchange Commission
May 7, 1997
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except to the extent set forth in applicable Partnership Agreement and the
Delaware Act, fully paid and non-assessable.

         The opinion expressed above is subject in all respects to the following
assumptions, exceptions and qualifications:

1.       We have assumed that (i) all signatures on all documents examined by us
         are genuine, (ii) all documents submitted to us as originals are
         accurate and complete, (iii) all documents submitted to us as copies
         are true and correct copies of the originals thereof, (iv) all
         information submitted to us is accurate and complete as of the date
         hereof, (v) all persons executing and delivering documents reviewed by
         us were competent to execute and to deliver such documents, and (vi)
         that all persons signing, in a representative capacity, documents
         reviewed by us had authority to sign in such capacity.

2.       We have assumed, with respect to the Interests in the Partnership, that
         all conditions relating to the sale of Interests in the Partnership and
         the admission of the subscribers therefor as limited partners or
         general partners, as the case may be, of the Partnership, as specified
         in the Registration Statement and the Subscription Documents (as such
         term is defined in the Registration Statement), including receipt of
         the full amount of consideration for those Interests, have been
         fulfilled.

3.       We have assumed, with respect to the Interests in the Partnership, that
         the Registration Statement will have been declared effective under the
         Securities Act and that no stop order suspending the effectiveness of
         the Registration Statement will have been issued by the Commission and
         no proceedings for that purpose will have been instituted by the
         Commission prior to the issuance of the Interests in the Partnership.

4.       We have assumed, with respect to the Partnership, that a Certificate of
         Limited Partnership for the Partnership has been executed and filed
         with the Secretary of State of the State of Delaware in accordance with
         the Delaware Act and as specified in the Registration Statement.

5.       We have assumed, with respect to the Partnership, that there are no
         agreements, indentures, mortgages, deeds of trust or instruments that
         affect the ability of the Partnership to issue Interests therein.

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Securities and Exchange Commission
May 7, 1997
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6.       This opinion speaks as of the date hereof and is limited to the matters
         expressly set forth herein, and no opinion is implied or may be
         inferred beyond such matters.

     The opinions expressed above are limited to the laws of the State of Texas,
the Delaware Act, and the federal laws of the United States of America.

     We know that we are referred to under the headings "Tax Aspects" and "Legal
Opinions" in the Prospectus forming a part of the Registration Statement and
filed with the Commission pursuant to the Act, and we hereby consent to that use
of our name in the Registration Statement, including any amendment thereof or
supplements thereto, and to the filing of this opinion as an exhibit to the
Registration Statement. In giving this consent, we do not hereby admit that we
come into the category of persons whose consent is required under Section 7 of
the Act or the rules and regulations of the Commission promulgated thereunder.

     This firm disclaims any duty to advise you regarding any changes in, or
to otherwise communicate with you with respect to, the matters addressed herein.

                                             Very truly yours,




                                             /s/ Vinson & Elkins L.L.P.
                                             ---------------------------------
                                             VINSON & ELKINS L.L.P.