1
                                                                       EXHIBIT 8


                     [LETTERHEAD OF VINSON & ELKINS L.L.P.]

                                 August 1, 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. (the
"Partnership") in connection with the public offering (the "Offering") of
3,800,000 common units representing limited partner interests ("Common Units")
in the Partnership by Cub Investment, LLC, Haddington/Chase Energy Partners
(Bear Paw) LP, Jonathan Nixon, Chris Conley, Nancy Rife, Stephanie Swanson and
R&K Ventures LLLP (the "Selling Unitholders"), and up to 570,000 additional
common units by certain of the Selling Unitholders pursuant to an over-allotment
option granted to the underwriters. The Offering of such Common Units is under
the Partnership's Registration Statement on Form S-3 (Registration No.
333-63566) (the "Registration Statement"), as supplemented by the Prospectus
Supplement filed with the Securities and Exchange Commission pursuant to Rule
424(b) under the Securities Act of 1933 (the "Prospectus Supplement"). In
connection therewith, we have reviewed the discussion (the "Discussion") set
forth under the caption "Tax Considerations" in the Registration Statement, as
supplemented by the discussion set forth under the caption "Prospectus
Supplement Summary - Tax Considerations" in the Prospectus Supplement.

         The Discussion is accurate and complete in all material respects and
constitutes our opinion, which is subject to the assumptions and qualifications
set forth therein, as to the material tax consequences to purchasers of Common
Units pursuant to the Offering. We assume no obligation to update this opinion.

         We hereby consent to the filing of this opinion as an exhibit to a
Current Report on Form 8-K of the Partnership, the incorporation by reference of
this opinion in the Registration Statement and the references to our firm and
this opinion contained in the prospectus supplement forming a part of the
Registration Statement. The issuance of this consent does not concede that we
are an "Expert" for the purposes of the Securities Act of 1933.


                                             Very truly yours,

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

                                             Vinson & Elkins L.L.P.