Exhibit 5

                               September 20, 2002


Port Arthur Finance Corp.
1700 East Putnam Avenue
Suite 500
Old Greenwich, Connecticut 06870

Ladies and Gentlemen:

                  We have acted as counsel to Port Arthur Finance Corp., a
Delaware corporation (the "Company"), and to The Premcor Refining Group Inc., a
Delaware corporation, Sabine River Holding Corp., a Delaware corporation, Neches
River Holding Corp., a Delaware corporation, and Port Arthur Coker Company L.P.,
a Delaware limited partnership (each individually, a "Guarantor" and
collectively, the "Guarantors"), in connection with the Registration Statement
on Form S-4 (the "Registration Statement") filed by the Company and the
Guarantors with the Securities and Exchange Commission (the "Commission") under
the Securities Act of 1933, as amended, relating to the issuance by the Company
of $255 million aggregate principal amount of its 12.50% Senior Secured Notes
due 2009 (the "Exchange Securities") and the issuance by the Guarantors of
guarantees (the "Exchange Guarantees"), with respect to the Exchange Securities.
The Exchange Securities and the Exchange Guarantees will be issued under an
indenture (as supplemented, the "Indenture"), dated as of August 19, 1999, among
the Company, Sabine River Holding Corp., Neches River Holding Corp., Port Arthur
Coker Company L.P., HSBC Bank USA, as Capital Markets Trustee, and Deutsche Bank
Trust



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Company Americas (formerly Bankers Trust Company), as Collateral Trustee, as
supplemented by the first supplemental indenture, dated as of June 6, 2002,
among the Company, the Guarantors, the Capital Markets Trustee and the
Collateral Trustee. The Exchange Securities will be offered by the Company in
exchange for $255 million aggregate principal amount of its outstanding 12.50%
Senior Secured Notes due 2009 (the "Securities").

                  We have examined the Registration Statement and the Indenture,
which has been filed with the Commission as an exhibit to the Registration
Statement. We also have examined the originals, or duplicates or certified or
conformed copies, of such records, agreements, instruments and other documents
and have made such other and further investigations as we have deemed relevant
and necessary in connection with the opinions expressed herein. As to questions
of fact material to this opinion, we have relied upon certificates of public
officials and of officers and representatives of the Company and the Guarantors.

                  In rendering the opinions set forth below, we have assumed the
genuineness of all signatures, the legal capacity of natural persons, the
authenticity of all documents submitted to us as originals, the conformity to
original documents of all documents submitted to us as duplicates or certified
or conformed copies, and the authenticity of the originals of such latter
documents. We also have assumed that the Indenture is the valid and legally
binding obligation of the Capital Markets Trustee and the Collateral Trustee.

                  Based upon the foregoing, and subject to the qualifications
and limitations stated herein, we are of the opinion that:

                  1. When the Exchange Securities have been duly executed,
         authenticated, issued and delivered in accordance with the provisions
         of the Indenture upon the exchange, the Exchange Securities will
         constitute valid and legally binding obligations of the Company,



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         enforceable against the Company in accordance with their terms.

                  2. When the Exchange Securities have been duly executed,
         authenticated, issued and delivered in accordance with the provisions
         of the Indenture upon the exchange and the Exchange Guarantees have
         been duly issued, the Exchange Guarantees will constitute valid and
         legally binding obligations of the Guarantors, enforceable against the
         Guarantors in accordance with their terms.

                  Our opinions set forth above are subject to the effects of
bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium and
other similar laws relating to or affecting creditors' rights generally, general
equitable principles (whether considered in a proceeding in equity or at law)
and an implied covenant of good faith and fair dealing.

                  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, the Federal law of the United States, the Delaware General
Corporation Law and the Delaware Revised Uniform Limited Partnership Act.

                  We hereby consent to the filing of this opinion letter as
Exhibit 5 to the Registration Statement and to the use of our name under the
caption "Legal Matters" in the Prospectus included in the Registration
Statement.

                                Very truly yours,



                                /s/ SIMPSON THACHER & BARTLETT