<DOCUMENT>
<TYPE>EX-99.B
<SEQUENCE>3
<FILENAME>ex-b.txt
<DESCRIPTION>EXHIBIT B--POWER OF ATTORNEY
<TEXT>
                                    EXHIBIT B

                                POWER OF ATTORNEY

KNOW ALL PERSONS BY THESE PRESENTS, that SPO Partners II, L.P., SPO Advisory
Partners, L.P., San Francisco Partners II, L.P., SF Advisory Partners, L.P., SPO
Advisory Corp., John H. Scully, William E. Oberndorf and William J. Patterson
(each a "Grantor") have made, constituted and appointed, and by these presents
do make, constitute and appoint, each of William E. Oberndorf and Kim M. Silva
(each an "Attorney"), the true and lawful agent and attorney-in-fact, with full
power of substitution and resubstitution, of the Grantor, for and in Grantor's
name, place and stead, in any and all capacities, to do all or any of the
following acts, matters and things:

         1.   To sign on behalf of the Grantor statements on Schedule 13D or 13G
              or Forms 3, 4 and 5, or amendments thereto pursuant to Section
              13(d) or Section 16 under the Securities Exchange Act of 1934.

         2.   To do all such other acts and things as, in such Attorney's
              discretion, he or she deems appropriate or desirable for the
              purpose of filing such statements on Schedule 13D or 13G or Forms
              3, 4 and 5, or amendments thereto.

         3.   To appoint in writing one or more substitutes who shall have the
              power to act on behalf of the Grantor as if that substitute or
              those substitutes shall have been originally appointed Attorney
              (s) by this Power of Attorney and/or to revoke any such
              appointment at any time without assigning any reason therefor.

The Grantor hereby ratifies and confirms all that said agents and attorneys-in-
fact or any substitute or substitutes may lawfully do or cause to be done by
virtue hereof. This Power of Attorney shall remain in full force and effect
until the undersigned is no longer required to file Forms 3, 4 and 5 or to file
reports under Section 13(d) of the Securities Exchange Act of 1934 with respect
to the undersigned's holdings of and transactions in securities issued by Cabot
Corporation, unless earlier revoked by the undersigned in a signed writing
delivered to the foregoing attorneys-in-fact.

The words Grantor and Attorney shall include all grantors and attorneys under
this Power of Attorney.

                      [Signatures on the Following Pages.]

<PAGE>


IN WITNESS WHEREOF, each Grantor duly assents to this Power of Attorney by his,
her or its signature as of the 29th day of August, 2005.


                                        SPO PARTNERS II, L.P.

                                        By:  SPO Advisory Partners, L.P.
                                        Its:  General Partner

                                        By:  SPO Advisory Corp.
                                        Its: General Partner

                                        By: /s/ William E. Oberndorf
                                            ----------------------------
                                            Name:  William E. Oberndorf
                                            Title:  Vice President


                                        SF ADVISORY PARTNERS II, L.P.

                                        By:  SPO Advisory Corp.
                                        Its: General Partner

                                        By: /s/ William E. Oberndorf
                                            ----------------------------
                                            Name:  William E. Oberndorf
                                            Title:  Vice President


                                        SAN FRANCISCO PARTNERS II, L.P.

                                        By:  SF Advisory Partners, L.P.
                                        Its:  General Partner

                                        By:  SPO Advisory Corp.
                                        Its: General Partner

                                        By: /s/ William E. Oberndorf
                                            ----------------------------
                                            Name:  William E. Oberndorf
                                            Title:  Vice President



<PAGE>

                                        SF ADVISORY PARTNERS, L.P.

                                        By:  SPO Advisory Corp.
                                        Its: General Partner

                                        By: /s/ William E. Oberndorf
                                            ----------------------------
                                            Name:  William E. Oberndorf
                                            Title:  Vice President


                                        SPO ADVISORY CORP.

                                        By: /s/ William E. Oberndorf
                                            ----------------------------
                                            Name:  William E. Oberndorf
                                            Title:  Vice President


                                        JOHN H. SCULLY

                                        /s/ John H. Scully
                                        ------------------


                                        WILLIAM E. OBERNDORF

                                        /s/ William E. Oberndorf
                                        ----------------------------


                                        WILLIAM J. PATTERSON

                                        /s/ William J. Patterson
                                        ------------------------
</TEXT>
</DOCUMENT>
