EXHIBIT 8.1


                    [Simpson Thacher & Bartlett Letterhead]

                                       September 24, 1998



Clark Refining & Marketing, Inc.
8182 Maryland Avenue
St. Louis, Missouri 63105

Ladies and Gentlemen:

     We have acted as special counsel for Clark Refining & Marketing, Inc., a
Delaware corporation (the "Company"), in connection with the Registration
Statement on Form S-4 (the "Registration Statement") filed by the Company with
the Securities and Exchange Commission (the "Commission") under the Securities
Act of 1933, as amended (the "Securities Act"), relating to the issuance by the
Company of $110,000,000 aggregate principal amount of its 8-5/8% New Senior
Notes due 2008 (the "New Notes"), which are to be offered by the Company in
exchange for $110,000,000 aggregate principal amount of its outstanding 8-5/8%
Senior Notes, due 2008 (the "Old Notes").

     We have examined the Registration Statement and the Indenture which has
been filed with the Commission as an Exhibit to the Registration Statement. In
addition, we have examined, and have relied as to matters of fact upon, the
originals or copies, certified or otherwise identified to our satisfaction, of
such corporate records, agreements, documents and other instruments and such
certificates or comparable documents of public officials and of officers and
representatives of the Company, and have made such other and further
investigations, as we have deemed relevant and necessary as a basis for the
opinion hereinafter set forth.

 
Clark Refining & Marketing, Inc.      -2-                     September 24, 1998

     In such examination, we have assumed that the Indenture has been duly
authorized, executed and delivered by the Trustee. In addition, we have assumed
the genuineness of all signatures, the legal capacity of natural persons, the
authenticity of all documents submitted to us as originals and the conformity to
original documents of all documents submitted to us as certified or photostatic
copies, and the authenticity of the originals of such latter documents.

     Based upon the foregoing, and subject to the qualifications and limitations
stated herein, we hereby confirm that the statements set forth in the
Registration Statement under the caption "Certain United States Federal Income
Tax Consequences of the Exchange" insofar as they purport to constitute
summaries of United States federal tax law or legal conclusions with respect
thereto are accurate in all material respects.

     We are members of the Bar of the State of New York and we do not express
any opinion herein concerning any law other than the law of the State of New
York and the federal law of the United States. This opinion is rendered to you
solely in connection with the above-described transaction and may not be relied
upon for any other purpose without our prior written consent.

     We hereby consent to the use of this opinion as an Exhibit to the
Registration Statement and to the reference to our firm under the caption "Legal
Matters" in the Prospectus included therein.

                                 Very truly yours,
                                 /s/ Simpson Thacher & Bartlett
                                 SIMPSON THACHER & BARTLETT