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                                                                     EXHIBIT 5.1

                          Fulbright & Jaworski L.L.P.
                   A Registered Limited Liability Partnership

                           1301 McKinney, Suite 5100                Houston
                           Houston, Texas 77010-3095           Washington, D.C.
                                                                    Austin
Telephone: 713/651-5151                                          San Antonio
Facsimile: 713/651-5246                                             Dallas
                                                                   New York
                                                                  Los Angeles
                                                                  Minneapolis
                                                                    London
                                                                   Hong Kong

                                 August 28, 2001

Xanser Corporation
2435 North Central Expressway
Suite 700
Richardson, Texas  75080

Ladies and Gentlemen:

         We have acted as counsel for Xanser Corporation, a Delaware corporation
(the "Registrant"), in connection with the registration under the Securities Act
of 1933 of 2,000,000 shares of the Registrant's common stock, without par value
(the "Stock"), to be offered upon the terms and subject to the conditions set
forth in the Kaneb Services, Inc. 1994 Stock Incentive Plan, as amended (the
"Plan").

         In connection therewith, we have examined originals or copies certified
or otherwise identified to our satisfaction of the Registration Statement on
Form S-8 with respect to the Stock filed with the Securities and Exchange
Commission by the Registrant on August 28, 2001 (the "Registration Statement"),
the Restated Certificate of Incorporation of the Registrant, the Bylaws of the
Registrant and such other documents and instruments as we have deemed necessary
or appropriate for the expression of the opinions contained herein.

         We have assumed the authenticity and completeness of all records,
certificates and other instruments submitted to us as originals, the conformity
to original documents of all records, certificates and other instruments
submitted to us as copies, the authenticity and completeness of the originals of
those records, certificates and other instruments submitted to us as copies and
the correctness of all statements of fact contained in all records, certificates
and other instruments that we have examined.

         Based on the foregoing, and having regard for such legal considerations
as we have deemed relevant, we are of the opinion that the Stock has been duly
and validly authorized for issuance and, when issued in accordance with the
terms of the Plan, will be duly and validly issued, fully paid and
nonassessable.

         The opinions expressed herein relate solely to, are based solely upon
and are limited exclusively to the laws of the State of Texas and the federal
laws of the United States of America, to the extent applicable.

         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement.


                                       Very truly yours,

                                       /s/ FULBRIGHT & JAWORSKI L.L.P.

                                       Fulbright & Jaworski L.L.P.