EXHIBIT 5.1

                   (LETTERHEAD OF GIBSON, DUNN & CRUTCHER LLP)

                                 April 10, 2003






(303) 298-5700                                                     C 97394-00008

Northwest Pipeline Corporation
295 Chipeta Way
Salt Lake City, Utah  84108

         Re:      Northwest Pipeline Corporation
                  Registration Statement on Form S-4

Ladies and Gentlemen:

         We have acted as special counsel to Northwest Pipeline Corporation, a
Delaware corporation (the "Issuer"), in connection with the Issuer's
registration, on a Registration Statement on Form S-4 (the "Registration
Statement"), under the Securities Act of 1933, as amended, of $175,000,000
aggregate principal amount of 8 1/8% Senior Notes due 2010 (the "New Notes").

         The New Notes will be offered in exchange for like principal amounts of
the Issuer's outstanding 8 1/8% Senior Notes due 2010 (the "Old Notes") pursuant
to the Registration Rights Agreement, dated as of March 4, 2003 (the
"Registration Rights Agreement"), by and between the Issuer and Lehman Brothers
Inc., on behalf of itself and the Initial Purchasers listed on Schedule I
thereto. The Registration Rights Agreement was executed in connection with the
private placement of the Old Notes.

         The New Notes will be issued pursuant to the Indenture, dated as of
March 4, 2003 (the "Indenture"), by and between the Issuer and JPMorgan Chase
Bank, as Trustee. The New Notes and the Indenture are each governed under the
internal laws of the State of New York, and are sometimes collectively referred
to herein as the "Documents."

         In rendering this opinion, we have examined the Documents, and have
also made such inquiries and examined, among other things, originals or copies,
certified or otherwise identified



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April 10, 2003
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to our satisfaction, of such records, agreements, certificates, instruments and
other documents, as we have considered necessary or appropriate for purposes of
this opinion.

         In rendering this opinion, we have assumed:

         (a) Each party to the Documents (i) is a validly existing corporation
in good standing under the laws of its state of incorporation, (ii) has all
requisite power and authority to execute, deliver and perform its obligations
under the Documents, (iii) has duly authorized, by all necessary action on such
party's part, the execution and delivery of each such Document and the
performance of such obligations and (iv) has duly executed and delivered each
such Document;

         (b) Each of the Documents is the legal, valid and binding obligation
of, and is enforceable against, each party thereto (other than the Issuer, as to
which the assumptions in this clause (b) do not apply) in accordance with its
terms;

         (c) The signatures on all documents examined by us are genuine, all
individuals executing such documents had all requisite legal capacity and
competency and were duly authorized to execute and deliver such documents, the
documents submitted to us as originals are authentic, and the documents
submitted to us as certified or reproduction copies conform to the originals;

         (d) There are no agreements or understandings between or among the
Company and other parties to the Documents, or third parties, that would expand,
modify or otherwise affect the terms of the Documents or the respective rights
or obligations of the parties thereunder;

         (e) The proceeds from the sale of the Old Notes were applied as set
forth in the Offering Memorandum of the Company dated February 27, 2003 in
connection with the issuance and sale of the Old Notes; and

         (f) The issuance and delivery of the New Notes will not, at any time,
violate any applicable law or result in a violation of any provision of any
instrument or agreement then binding on the Issuer or any restriction imposed by
any court or governmental body having jurisdiction over the Issuer.

         Based upon the foregoing and in reliance thereon, and subject to the
assumptions, exceptions, qualifications and limitations contained herein, we are
of the opinion that when issued in exchange for the Old Notes pursuant to the
terms of the Indenture and the exchange offer described in the Registration
Statement, the New Notes will be legally issued and will constitute binding
obligations of the Issuer.

         The foregoing opinions are subject to the following exceptions,
qualifications and limitations:



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                  A. Our opinions are subject to (i) the effect of any
         bankruptcy, insolvency, reorganization, moratorium, arrangement or
         similar laws affecting the rights and remedies of creditors' generally
         (including, without limitation, the effect of statutory or other laws
         regarding fraudulent transfers or preferential transfers) and (ii)
         general principles of equity, including without limitation concepts of
         materiality, reasonableness, good faith and fair dealing and the
         possible unavailability of specific performance, injunctive relief or
         other equitable remedies regardless of whether enforceability is
         considered in a proceeding in equity or at law.

                  B. We express no opinion regarding the effectiveness (i) of
         any waiver (whether or not stated as such) under the Documents, or any
         consent thereunder relating to, any unknown future rights or the rights
         of any party thereto existing, or duties owing to it, as a matter of
         law; (ii) of any waiver (whether or not stated as such) contained in
         the Documents of rights of any party, or duties owing to it, that is
         broadly or vaguely stated or does not describe the right or duty
         purportedly waived with reasonable specificity; (iii) of provisions
         relating to indemnification, exculpation or contribution, (iv) of any
         provisions of the Documents that may be construed as penalties or
         forfeitures; or (v) of any covenants (other than covenants relating to
         the payment of principal, interest, premium, indemnities and expenses)
         in the Indenture to the extent they are construed to be independent
         requirements as distinguished from conditions to the declaration or
         occurrence of a default or any event of default.

                  C. We render no opinion herein as to matters involving the
         laws of any jurisdiction other than the State of New York and the
         United States of America, and this opinion is limited to the effect of
         the present state of the laws of the State of New York and the United
         States of America. We assume no obligation to revise or supplement this
         opinion in the event of changes in such laws or the interpretations
         thereof or in the event of changes in such facts.

                  D. We express no opinion as to the applicability to, or the
         effect of noncompliance by, the holders of the New Notes or the Trustee
         with any state or federal laws applicable to the transactions
         contemplated by the Documents because of the nature of the business of
         such party.





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April 10, 2003
Page 4


         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the reference to this firm under the heading
"Legal Matters" contained in the prospectus that forms a part of the
Registration Statement. In giving this consent, we do not admit that we are
within the category of persons whose consent is required under Section 7 of the
Securities Act of 1933, as amended, or the rules and regulations promulgated
thereunder.

                                             Very truly yours,

                                             /s/ Gibson, Dunn & Crutcher LLP

                                             GIBSON, DUNN & CRUTCHER LLP



RMR/CMN