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                                                                     Exhibit 5.1


                      [Letterhead of Haynes and Boone, LLP]

September 17, 2002

Harken Energy Corporation
580 WestLake Park Boulevard
Suite 600
Houston, Texas 77079

Re:  Registration Statement on Form S-3

Dear Sirs:

We have acted as counsel for Harken Energy Corporation, a Delaware corporation
(the "Company"), in connection with the filing of a registration statement on
Form S-3 under the Securities Act of 1933, as amended ("Registration
Statement"), with respect to 16,824,000 shares of its Common Stock, par value
$0.01 per share (the "Shares"). Of the Shares, 14,824,000 Shares are issuable
upon the conversion of the Company's 7% Senior Convertible Notes Due 2007 (the
"Notes") pursuant to the Terms and Conditions ("Terms and Conditions") of the
respective Notes, such Shares being referred to as the "7% Notes Shares." The
remaining 2,000,000 Shares were issued in connection with the partial redemption
of the Company's 5% Senior Convertible Note Due 2003 in the original principal
amount of $6,803,629.26 ("5% Note"), such Shares being referred to herein as the
"5% Note Shares."

We have examined originals or copies, certified or otherwise identified, of such
documents, corporate records and other instruments as we have deemed necessary
or advisable for purposes of this opinion. As to matters of fact, we have
examined and relied upon such corporate records and documents of the Company as
we have deemed necessary or appropriate to render this opinion and, where we
have deemed appropriate, representations or certificates related to factual
matters of officers of the Company or public officials. We have assumed the
authenticity of all documents submitted to us as originals, the genuineness of
all signatures, the legal capacity of natural persons and the conformity to the
originals of all documents submitted to us as copies. As to various questions of
fact material to this opinion, where such facts have not been independently
established, and as to the content and form of the Certificate of Incorporation,
the Bylaws, certain minutes, records, resolutions and other documents or
writings of the Company, we have relied, to the extent we have deemed reasonably
appropriate, upon representations or certificates of officers of the Company or
governmental officials and upon documents, records and instruments furnished to
us by the Company, without independent check or verification of their accuracy.

Based on the foregoing and subject to the limitations, qualifications,
exceptions and assumptions set forth herein, we are of the opinion that the
Shares have been duly authorized for issuance. The 5% Note Shares are validly
issued, fully paid and non-assessable shares of the Company's Common Stock. When
the 7% Notes Shares have been issued and paid for in accordance with the Terms
and Conditions of the respective Notes, such Shares will be validly issued,
fully paid and non-assessable shares of the Company's Common Stock.

The opinions expressed above are specifically limited to the General Corporation
Laws, as amended, of the State of Delaware and the federal laws of the United
States of America. General Corporation Laws shall for this purpose be deemed to
include all applicable provisions of the Delaware General Corporation Law as
currently in effect, the terms of the Delaware Constitution, and all judicial
decisions of the Court of Chancery of the State of Delaware.

This opinion (i) is rendered in connection with the filing of the Registration
Statement, (ii) is rendered as of the date hereof, and we undertake no, and
hereby disclaim any kind of obligation to advise you of any change or any new
developments that might affect any matters or opinions set forth herein, and
(iii) is limited to the matters stated herein and no opinions may be inferred or
implied beyond the matters expressly stated herein.

We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the references to our Firm's name therein.

Very truly yours,

/s/ Haynes and Boone, LLP

Haynes and Boone, LLP