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                                                                     EXHIBIT 5.1

                    [FULBRIGHT & JAWORSKI L.L.P. LETTERHEAD]

April 27, 2001

Lakehead Pipe Line Company, Inc.
Lake Superior Place 21 West Superior Street
Duluth, Minnesota 55802

Gentlemen:

     We have acted as counsel to Lakehead Pipe Line Partners, L.P., a Delaware
limited partnership (the "Partnership"), and Lakehead Pipe Line Company, Inc., a
Delaware corporation and the general partner of the Partnership, in connection
with the registration under the Securities Act of 1933, as amended (the "Act"),
of the offering and sale of up to an aggregate of $500,000,000 of Class A Common
Units representing Class A limited partner interests in the Partnership (the
"Class A Common Units"). As the basis for the opinion hereinafter expressed, we
have examined such statutes, regulations, corporate records and documents,
certificates of corporate and public officials, and other instruments as we have
deemed necessary or advisable for the purposes of this opinion. In such
examination we have assumed the authenticity of all documents submitted to us as
originals and the conformity with the original documents of all documents
submitted to us as copies. Based on the foregoing and on such legal
considerations as we deem relevant, we are of the opinion that:

     1.   The Partnership has been duly formed and is an existing limited
          partnership under the Delaware Revised Uniform Limited Partnership
          Act.

     2.   The Class A Common Units will, when issued and paid for as described
          in the Partnership's Registration Statement on Form S-3 relating to
          the Class A Common Units (the "Registration Statement"), be duly
          authorized, validly issued, fully paid and nonassessable, except as
          such nonassessability may be affected by the matters described in the
          Partnership's Form 8-A, as amended, under the caption "Item 1.
          Description of Registrant's Securities to be Registered," which is
          incorporated by reference in the Prospectus included in the
          Registration Statement.

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     We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the reference to us under the caption "Validity
of Class A Units" in the Prospectus. This opinion may be incorporated by
reference in a registration statement of the Partnership relating to the
registration of additional Class A Common Units pursuant to Rule 462(b) under
the Securities Act, in which case the opinions expressed herein will apply to
the additional units registered thereunder.


                                                 Very truly yours,


                                                 Fulbright & Jaworski L.L.P.