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                       OPINION OF VINSON & ELKINS L.L.P.

                                                                       EXHIBIT 5

                                 JUNE 21, 2001

NORTHERN BORDER PARTNERS, L.P.
1400 SMITH STREET
HOUSTON, TEXAS 77002

Ladies and Gentlemen:

     We have acted as counsel to Northern Border Partners, L.P., a Delaware
limited partnership (the "Partnership"), in connection with the registration of
5,711,901 units representing common limited partner interests in the Partnership
(the "common units") on behalf of certain offering unitholders pursuant to the
Registration Statement on Form S-3 (the "Registration Statement") to be filed
with the Securities and Exchange Commission under the Securities Act of 1933. We
have examined the Registration Statement, the Amended and Restated Agreement of
Limited Partnership of the Partnership (the "Partnership Agreement"), the
Certificate of Limited Partnership of the Partnership (the "Certificate") filed
with the Secretary of State of Delaware pursuant to the Delaware Revised Uniform
Limited Partnership Act in connection with the formation of the Partnership and
such other documents as we have deemed necessary or appropriate for purposes of
this opinion. In addition, we have reviewed certain certificates of officers of
the general partners of the Partnership and of public officials, and we have
relied on such certificates with respect to certain factual matters that we have
not independently established.

     Based upon the foregoing and subject to the limitations and assumptions set
forth herein, we are of the opinion that:

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

          2. All of the common units offered by means of the Registration
     Statement have been duly authorized by the Partnership Agreement and
     legally issued and are fully paid and non-assessable, except as such
     non-assessability may be affected by 17-607 of the Delaware Revised Uniform
     Limited Partnership Act.

     The opinions expressed herein are qualified in the following respects:

          (A) We have assumed, without independent verification, that the
     certificates for the common units will conform to the specimens thereof
     examined by us and will have been duly countersigned by a transfer agent
     and duly registered by a registrar of the common units.

          (B) We have assumed that (i) each document submitted to us for review
     is accurate and complete, each such document that is an original is
     authentic, each such document that is a copy conforms to an authentic
     original and all signatures on each such document are genuine, and (ii)
     each certificate from governmental officials reviewed by us is accurate,
     complete and authentic, and all official public records are accurate and
     complete.

          (C) This opinion is limited in all respects to federal laws and the
     Delaware Revised Uniform Limited Partnership Act.

     We are rendering this opinion as of the time the Registration Statement
becomes effective. We hereby consent to the use of our name in the Registration
Statement and to the filing of this opinion as an exhibit to the Registration
Statement. This consent does not constitute an admission that we are "experts"
within the meaning of such term as used in the Securities Act of 1933.

                                            Very truly yours,

                                            /s/ VINSON & ELKINS L.L.P.
                                            Vinson & Elkins L.L.P.