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                                                                     Exhibit 5.1



May 27, 1998





Harken Energy Corporation
5605 N. MacArthur Blvd
Suite 400
Irving, TX  75038

       Re:    Registration Statement on Form S-3

Gentlemen:

       I have acted as counsel to Harken Energy Corporation, a Delaware
corporation (the "Company"), in connection with the registration under the
Securities Act of 1933, as amended (the "Act"), of the offer and sale of an
aggregate of 5,751,073 shares (the "Shares") of common stock, $.01 par value per
share, of the Company ("Common Stock") pursuant to a Registration Statement on
Form S-3 of the Company (the "Registration Statement") to which this opinion
letter is an exhibit. The Shares include 5,733,073 shares of Common Stock that
are being registered pursuant to a Securities Purchase Agreement (the
"Securities Purchase Agreement") dated as of April 9, 1998, by and between the
Company and RGC International Investors, LDC ("RGC"), which requires the
registration of shares of Common Stock issuable upon exercise of the Company's
Series F Convertible Preferred Stock (the "Preferred Shares") and shares of
Common Stock which may be issued to RGC pursuant to options granted to RGC under
the Securities Purchase Agreement (the "Option Shares").

       In reaching the opinion set forth herein, I have reviewed (a) the
Registration Statement, (b) the Certificate of Incorporation of the Company, as
amended, (c) the Bylaws of the Company, (d) records of proceedings of the Board
of Directors and the stockholders of the Company and (e) except as set forth
below, such other agreements, certificates of public officials and officers of
the Company, records, documents and matters of law that I deemed relevant.

       Based on and subject to the foregoing and subject further to the
assumptions, exceptions and qualifications hereinafter stated, I am of the
opinion that, subject to compliance with federal and state securities laws (as
to which I express no opinion), the Shares that are currently outstanding, have
been duly authorized and validly issued and are fully paid and nonassessable. I
am further of the opinion that the Shares, upon issuance in accordance with the
terms of the Securities Purchase Agreement and the Certificate of Designations,
Preferences and Rights of Series F Convertible Preferred Stock, and the Option
Shares, upon issuance in accordance with the terms of the Securities Purchase
Agreement and upon full payment for the purchase price thereof, will be duly
authorized, validly issued, fully paid and nonassessable.

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

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


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Harken Energy Corporation
May 27, 1998
Page 2

              all persons signing, in a representative capacity, documents
              reviewed by me had authority to sign in such capacity.

       b.     I have assumed that there are no agreements, indentures,
              mortgages, deeds of trust or instruments that affect the ability
              of the Company to issue the Shares.

       The opinions expressed above are limited to the laws of the State of
Texas, the General Corporation Law of the State of Delaware and the federal laws
of the United States of America. You should be aware that I am not admitted to
the practice of law in the State of Delaware and my opinion herein as to the
General Corporation Law of the State of Delaware is based solely upon the
unofficial compilation thereof contained in Prentice Hall Information Services
Corporation Statutes.

       This opinion letter may be filed as an exhibit to the Registration
Statement. In giving this consent, I do not thereby admit that I come into the
category of persons whose consent is required under Section 7 of the Act or the
rules and regulations of the Securities and Exchange Commission promulgated
thereunder.

       I disclaim 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/ Gregory S. Porter
                                              Gregory S. Porter, Esq.