Document:

<PAGE>

                                  EXHIBIT 10.4

                                 AMENDMENT NO. 3

                                       TO

 THE EXPANDED AND AMENDED THYMOSIN ALPHA 1 LICENSE, DISTRIBUTORSHIP AND
                                SUPPLY AGREEMENT
        SIGNED BY AND BETWEEN SCICLONE PHARMACEUTICALS INTERNATIONAL LTD
                                       AND
         SIGMA-TAU INDUSTRIE FARMACEUTICHE RIUNITE SPA ON MARCH 3, 2000
       AS AMENDED BY THE PARTIES WITH AMENDMENT NO. 1 ON DECEMBER 19, 2001
            AND FURTHER AMENDED WITH AMENDMENT NO. 2 ON MAY 20, 2004
                          (HEREINAFTER "THE AGREEMENT")

SCICLONE PHARMACEUTICALS INTERNATIONAL LTD. ("SPIL"), a Cayman Islands business
entity which is a wholly-owned subsidiary of SciClone Pharmaceuticals, Inc.
("SCLN"), a Delaware corporation;

                                       and

SIGMA-TAU INDUSTRIE FARMACEUTICHE RIUNITE S.P.A. ("Sigma-Tau"), an Italian
corporation having offices at viale Shakespeare 47, 00144 Rome, Italy.

SPIL AND SIGMA-TAU HEREBY AGREE TO AMEND ARTICLE 5 (DEVELOPMENT AND CLINICAL
TRIALS), OF THE AGREEMENT IN ORDER TO ADD AN ADDITIONAL OBLIGATION "(5)" TO
SECTION 5.8, C, II AS FOLLOWS:

(c) SPIL'S Obligations

In furtherance of the Trial:

                              (i) SPIL shall supply free of charge to Sigma-Tau
the Licensed Product, placebo and the Roche products Pegaysy(R) and Copegus(R)
in the amounts needed for the Trial;

                              (ii) SPIL shall make payments to Sigma-Tau up to a
total of US $2,500,000 (U.S. Dollars two million five hundred thousand) to
assist in paying for incurred or anticipated costs and expenses associated with
the Trial, as follows:

<PAGE>

                                    (1) an initial payment equal to [****] upon
[****];

                                    (2) a payment equal to [****] upon [****];

                                    (3) a payment of [****] per each patient,
who is enrolled and injected with active drug substance, up to a cumulative
total of [****], paid [****]; and

                                    (4) a milestone payment equal to [****] upon
[****].

                                    (5) a milestone payment equal to U.S.
$1,500,000 (U.S. Dollars one million five hundred thousand) upon completion of
the final study report.

Except only as set forth above, all of the provisions of the Agreement shall
remain unchanged and in full force and effect.

SIGNATURES

IN WITNESS WHEREOF, THE PARTIES HERETO HAVE CAUSED THIS AMENDMENT AGREEMENT TO
BE DULY EXECUTED EFFECTIVE AS OF THE DATE LAST WRITTEN BELOW.

SCICLONE Pharmaceuticals                       SIGMA-TAU Industrie
International Ltd.                             Farmaceutiche Riunite SpA

____________________________                   _________________________________
By:                                            By:
Title:                                         Title:
Date:                                          Date:

*Certain information on this page has been omitted and filed separately with the
Commission. Confidential treatment has been requested with respect to the
omitted portions.<PAGE>

                                                                    EXHIBIT 10.1

                                                                  EXECUTION COPY

                          REGISTRATION RIGHTS AGREEMENT

                                     BETWEEN

                            BURLINGTON RESOURCES INC.

                                       AND

                             BANK OF AMERICA, N.A.,

                    AS TRUSTEE OF PERMIAN BASIN ROYALTY TRUST

                            DATED AS OF JULY 21, 2004

<PAGE>

      REGISTRATION RIGHTS AGREEMENT (the "AGREEMENT") dated as of July 21, 2004
by and between Burlington Resources Inc., a corporation formed under the laws of
the State of Delaware (the "COMPANY"), and Bank of America, N.A., as trustee
(the "TRUSTEE") of Permian Basin Royalty Trust, a trust formed under the laws of
the State of Texas (the "TRUST").

                                    RECITALS:

      WHEREAS, the Company is the owner, directly or indirectly, of 27,577,741
units of beneficial interest of the Trust ("TRUST UNITS"); and

      WHEREAS, the Trustee has agreed to file a registration statement or
registration statements relating to the sale by the Company and its Transferees
(as defined below) of the Trust Units;

      NOW, THEREFORE, in consideration of the premises and the covenants
hereinafter contained and for other good and valuable consideration, the receipt
and sufficiency of which are hereby acknowledged, and intending to be legally
bound hereby, it is agreed as follows:

      SECTION 1. Definitions. As used in this Agreement, the following terms
shall have the following meanings:

      "AGREEMENT" has the meaning set forth in the preamble hereof.

      "BUSINESS DAY" means each Monday, Tuesday, Wednesday, Thursday and Friday
that is not a day on which banking institutions in The City of New York are
authorized or obligated by law or executive order to close.

      "COMPANY" has the meaning set forth in the preamble hereof.

      "DEFERRAL NOTICE" has the meaning set forth in Section 3(j) hereof.

      "DEFERRAL PERIOD" has the meaning set forth in Section 3(j) hereof.

      "DEMAND NOTICE" has the meaning set forth in Section 2(a) hereof.

      "DEMAND REGISTRATION" has the meaning set forth in Section 2(a) hereof.

      "EFFECTIVE PERIOD" means the period commencing on the date hereof and
ending on the date that all Registrable Securities have ceased to be Registrable
Securities.

      "EXCHANGE ACT" means the Securities Exchange Act of 1934, as amended, and
the rules and regulations of the SEC promulgated thereunder.

      "EXPENSES" has the meaning set forth in Section 6(a) hereof.

      "HOLDER" shall mean the Company, and any Transferee of the Company to whom
Registrable Securities are permitted to be transferred in accordance with the
terms of this Agreement, and, in each case, who continues to be entitled to the
rights of a Holder hereunder.

<PAGE>

      "INDEMNIFIED PARTY" has the meaning set forth in Section 6(c) hereof.

      "INDEMNIFYING PARTY" has the meaning set forth in Section 6(c) hereof.

      "MATERIAL EVENT" has the meaning set forth in Section 3(j) hereof.

      "PIGGYBACK REGISTRATION" has the meaning set forth in Section 2(b) hereof.

      "PROSPECTUS" means the prospectus included in any Registration Statement
(including, without limitation, a prospectus that discloses information
previously omitted from a prospectus filed as part of an effective registration
statement in reliance upon Rule 430A promulgated under the Securities Act), as
amended or supplemented by any amendment or prospectus supplement, including
post-effective amendments, and all materials incorporated by reference or
explicitly deemed to be incorporated by reference in such Prospectus.

      "REGISTRABLE SECURITIES" means the Trust Units initially held by the
Company and any securities into or for which such Trust Units have been
converted or exchanged, and any security issued with respect thereto upon any
dividend, split or similar event until, in the case of any such security, the
earliest of (i) its effective registration under the Securities Act and resale
in accordance with the Registration Statement covering it, (ii) its sale to the
public pursuant to Rule 144 (or any similar provision then in force, but not
Rule 144A) under the Securities Act if the transferee thereof does not receive
"restricted securities" as defined in Rule 144, (iii) its sale in a private
transaction in which the transferor's rights under this Agreement are not
assigned to the transferee of the Securities and (iv) it becomes eligible for
resale pursuant to Rule 144(k) (or any similar rule then in effect under the
Securities Act).

      "REGISTRATION STATEMENT" means any registration statement of the Trust,
including any Shelf Registration Statement, that covers any of the Registrable
Securities pursuant to the provisions of this Agreement, including the
Prospectus, amendments and supplements to such registration statement, including
post-effective amendments, all exhibits and all materials incorporated by
reference or explicitly deemed to be incorporated by reference in such
registration statement.

      "REQUIRED INFORMATION" has the meaning set forth in Section 4 hereof.

      "RULE 144" means Rule 144 under the Securities Act, as such Rule may be
amended from time to time, or any similar rule or regulation hereafter adopted
by the SEC.

      "RULE 144A" means Rule 144A under the Securities Act, as such Rule may be
amended from time to time, or any similar rule or regulation hereafter adopted
by the SEC.

      "SEC" means the Securities and Exchange Commission.

      "SECURITIES ACT" means the Securities Act of 1933, as amended, and the
rules and regulations promulgated by the SEC thereunder.

                                       2
<PAGE>

      "SHELF REGISTRATION STATEMENT" means a Registration Statement for an
offering to be made on a delayed or continuous basis pursuant to Rule 415 under
the Securities Act registering the resale of Registrable Securities from time to
time by Holders thereof.

      "SPECIAL COUNSEL" means Andrews Kurth LLP or one such other successor
counsel as shall be specified by the Holders of a majority of all Registrable
Securities.

      "TRANSFEREE" has the meaning set forth in Section 9(d) hereof.

      "TRUST" has the meaning set forth in the preamble hereof.

      "TRUST UNITS" has the meaning set forth in the preamble hereof.

      "TRUSTEE" has the meaning set forth in the preamble hereof.

      SECTION 2. Demand Registration Rights.

      (a) During the Effective Period, the Company and any Transferee thereof to
whom a Demand Registration has been transferred in accordance with Section 9(d)
hereof may request, by written notice to the Trustee (the "DEMAND NOTICE"), that
the Trustee effect the registration under the Securities Act of the number of
Registrable Securities requested to be so registered pursuant to the terms and
conditions set forth in this Agreement (each a "DEMAND REGISTRATION"). Following
receipt of a Demand Notice for a Demand Registration, the Trustee shall use its
reasonable best efforts to file a Registration Statement as promptly as
practicable and shall use its reasonable best efforts to cause such Registration
Statement to be declared effective under the Securities Act as promptly as
practicable after the filing thereof. All requests made pursuant to this Section
2 will specify the number of Registrable Securities to be registered and the
intended methods of disposition thereof.

      The Company shall be entitled to a maximum of three (3) Demand
Registrations, which shall include (i) any Demand Registrations for registration
pursuant to a Shelf Registration Statement and (ii) any Demand Registrations
that are transferred to a Transferee in accordance with Section 9(d) hereof. No
Demand Registration shall be deemed to have occurred for purposes of this
Section 2(a) if the Registration Statement relating thereto does not become
effective or is not maintained effective for the period required pursuant to
Section 2(d).

      (b) In the event that any Demand Registration is transferred to a
Transferee in accordance with Section 9(d) hereof, and such Transferee sends a
Demand Notice to the Trustee, such Trustee will give notice to the Company (in
the event that it still is a Holder of Registrable Securities) of such Demand
Registration. Such notice shall describe such securities and specify the form,
manner and other relevant aspects of such proposed registration. The Company
may, by written response delivered to the Trustee within twenty (20) days after
the receipt by the Company of any such notice, request that all or a specified
part of the Registrable Securities held by the Company be included in such
Demand Registration (a "PIGGYBACK REGISTRATION"). Such response shall also
specify the intended method of disposition of such Registrable Securities. The
Trustee thereupon will use its reasonable commercial efforts to effect the
registration under the Securities Act of all Registrable Securities which the
Trustee has been so requested to register by the holders of Registrable
Securities to the extent required to permit the disposition (in

                                       3
<PAGE>

accordance with the intended methods thereof as aforesaid) of the Registrable
Securities to be so registered. No registration of Registrable Securities of the
Company effected by Piggyback Registration under this Section 2(b) shall relieve
the Trustee of any of its obligations to effect registrations of Registrable
Securities of the Company pursuant to, or reduce the total number of Demand
Registrations to which the Company continues to remain entitled under, Section
2(a) hereof.

      (c) If any of the Registrable Securities registered pursuant to a Demand
Registration are to be sold in a firm commitment underwritten offering, and the
managing underwriter or underwriters advise the Holders of such securities in
writing that in its view the total number or dollar amount of Registrable
Securities proposed to be sold in such offering is such as to adversely affect
the success of such offering (including, without limitation, securities proposed
to be included by other Holders of Registrable Securities entitled to include
securities in such Registration Statement pursuant to incidental or piggyback
registration rights), then there shall be included in such firm commitment
underwritten offering the number or dollar amount of Registrable Securities that
in the opinion of such managing underwriter can be sold without adversely
affecting such offering, and such number of Registrable Securities shall be
allocated as follows:

            (i) first, the securities for which inclusion in such Demand
      Registration for which the Demand Notice was submitted by such Holder; and

            (ii) second, the securities for which inclusion in any Piggyback
      Registration for which a notice was submitted in accordance with this
      Agreement.

      (d) The Trustee shall use reasonable commercial efforts to maintain the
effectiveness of the Registration Statement with respect to any Demand
Registration for a period of at least one hundred eighty (180) days (or three
years if a Shelf Registration Statement is requested) after the effective date
thereof or such shorter period in which all Registrable Securities included in
such Registration Statement have actually been sold or all Registrable
Securities have ceased to be Registrable Securities; provided, however, that
such period shall be extended for a period of time equal to the period the
holder of Registrable Securities refrains from selling any securities included
in such registration at the request of the Trust pursuant to this Agreement.

      (e) Notwithstanding the foregoing, if the Trustee shall furnish to the
Holders requesting a registration pursuant to this Section 2 within 30 days of
receiving such request a certificate signed by the Trustee stating that in the
good faith judgment of the Trustee it would be detrimental to the Trust and its
unitholders for such Registration Statement to be filed and it is therefore
beneficial to defer the filing of such Registration Statement, the Trustee shall
have the right to defer such filing for up to 2 periods of not more than 30 days
each after receipt of the request of the Holders; provided, however, that the
Trustee may not use this right more than once (for a total of up to 60 days) in
any 12-month period.

                                       4
<PAGE>

      SECTION 3. Registration Procedures. In connection with the registration
obligations of the Trustee under Section 2 hereof, during the Effective Period,
the Trustee shall:

            (a) Prepare and file with the SEC a Registration Statement or
      Registration Statements, including if so requested by the Holders a Shelf
      Registration Statement, on any appropriate form under the Securities Act
      available for the sale of the Registrable Securities by the Holders
      thereof in accordance with the intended method or methods of distribution
      thereof, and use its reasonable commercial efforts to cause each such
      Registration Statement to become effective and remain effective as
      provided herein; provided that before filing any Registration Statement or
      Prospectus or any amendments or supplements thereto with the SEC (but
      excluding reports filed with the SEC under the Exchange Act), furnish to
      the Holders, the Special Counsel and the managing underwriter or
      underwriters, if any, copies of all such documents proposed to be filed at
      least three (3) Business Days prior to the filing of such Registration
      Statement or amendment thereto or Prospectus or supplement thereto.

            (b) Subject to Section 3(j), prepare and file with the SEC such
      amendments and post-effective amendments to each Registration Statement as
      may be necessary to keep such Registration Statement continuously
      effective during the period provided herein with respect to the
      disposition of all securities covered by such Registration Statement;
      cause the related Prospectus to be supplemented by any required prospectus
      supplement, and as so supplemented to be filed pursuant to Rule 424 (or
      any similar provisions then in force) under the Securities Act; and use
      its reasonable commercial efforts to comply with the provisions of the
      Securities Act applicable to the Trust with respect to the disposition of
      all securities covered by such Registration Statement during the period
      provided herein with respect to the disposition of all securities covered
      by such Registration Statement in accordance with the intended methods of
      disposition by the sellers thereof set forth in such Registration
      Statement as so amended or such Prospectus as so supplemented.

            (c) Subject to Section 3(j), from and after the date a Registration
      Statement is declared effective, the Trustee shall, as promptly as
      practicable after the date the Required Information (as defined below) is
      delivered pursuant to Section 4 hereof and in accordance with this Section
      3(c):

                  (i) if required by applicable law, file with the SEC a
            post-effective amendment to the Registration Statement or prepare
            and, if required by applicable law, file a supplement to the related
            Prospectus or a supplement or amendment to any document incorporated
            therein by reference or file any other required document so that the
            Holder delivering such Required Information is named as a selling
            securityholder in the Registration Statement and the related
            Prospectus in such a manner as to permit such Holder to deliver such
            Prospectus to purchasers of the Registrable Securities in accordance
            with applicable law and, if the Trustee shall file a post-effective
            amendment to the Registration Statement, use its reasonable
            commercial efforts to cause such post-effective amendment to be
            declared effective under the Securities Act as promptly as is
            practicable; and

                                       5
<PAGE>

                  (ii) provide such Holder copies of any documents filed
            pursuant to Section 3(c)(i);

provided, that, if the Required Information is delivered during a Deferral
Period, the Trustee shall so inform the Holder delivering such Required
Information. The Trustee shall notify such Holder as promptly as practicable
after the effectiveness under the Securities Act of any post-effective amendment
filed pursuant to Section 3(c)(i). Notwithstanding anything contained herein to
the contrary, the Trustee shall be under no obligation to name any Holder that
has failed to deliver the Required Information in the manner set forth in
Section 4 hereof as a selling securityholder in any Registration Statement or
related Prospectus.

            (d) As promptly as practicable give notice to the Holders, the
      Special Counsel and the managing underwriter or underwriters, if any, (i)
      when any Prospectus, prospectus supplement, Registration Statement or
      post-effective amendment to a Registration Statement has been filed with
      the SEC and, with respect to a Registration Statement or any
      post-effective amendment, when the same has been declared effective, (ii)
      of any request, following the effectiveness of any Registration Statement
      under the Securities Act, by the SEC or any other federal or state
      governmental authority for amendments or supplements to any Registration
      Statement or related Prospectus, (iii) of the issuance by the SEC or any
      other federal or state governmental authority of any stop order suspending
      the effectiveness of any Registration Statement or the initiation or
      threatening of any proceedings for that purpose, (iv) of the receipt by
      the Trustee of any notification with respect to the suspension of the
      qualification or exemption from qualification of any of the Registrable
      Securities for sale in any jurisdiction or the initiation or threatening
      of any proceeding for such purpose, (v) of the occurrence of, but not the
      nature of or details concerning, a Material Event (as defined below) and
      (vi) of the determination by the Trustee that a post-effective amendment
      to a Registration Statement will be filed with the SEC, which notice may,
      at the discretion of the Trustee (or as required pursuant to Section
      3(j)), state that it constitutes a Deferral Notice (as defined below), in
      which event the provisions of Section 3(j) shall apply.

            (e) Use its reasonable commercial efforts to obtain the withdrawal
      of any order suspending the effectiveness of a Registration Statement or
      the lifting of any suspension of the qualification (or exemption from
      qualification) of any of the Registrable Securities for sale in any
      jurisdiction in which they have been qualified for sale, in either case as
      promptly as practicable, and provide prompt notice to each Holder of the
      withdrawal of any such order.

            (f) If requested by the managing underwriters, if any, or the
      Holders of the Registrable Securities being sold in connection with an
      underwritten offering, promptly include in a Prospectus supplement or
      post-effective amendment such information as the managing underwriters, if
      any, and such Holders may reasonably request in order to permit the
      intended method of distribution of such securities and make all required
      filings of such Prospectus supplement or such post-effective amendment as
      soon as practicable after the Trustee has received such request; provided,
      however, that the Trustee shall not be required to take any actions under
      this Section 3(f) that are not, in the opinion of counsel for the Trustee,
      in compliance with applicable law.

                                       6
<PAGE>

            (g) As promptly as practicable furnish to each Holder, the Special
      Counsel and each managing underwriter, if any, upon request, at least one
      (1) conformed copy of the Registration Statement and any amendment
      thereto, including exhibits and, if requested, all documents incorporated
      or deemed to be incorporated therein by reference.

            (h) Deliver to each Holder, the Special Counsel and each managing
      underwriter, if any, in connection with any sale of Registrable Securities
      pursuant to a Registration Statement as many copies of the Prospectus
      relating to such Registrable Securities (including each preliminary
      prospectus) and any amendment or supplement thereto as such persons may
      reasonably request; and the Trustee hereby consents (except during such
      periods that a Deferral Notice is outstanding and has not been revoked and
      subject to Section 3(j)(ii) hereof) to the use of such Prospectus or each
      amendment or supplement thereto by each Holder and the underwriters, if
      any, in connection with any offering and sale of the Registrable
      Securities covered by such Prospectus or any amendment or supplement
      thereto in the manner set forth therein.

            (i) Prior to any public offering of the Registrable Securities
      pursuant to a Registration Statement, use its reasonable commercial
      efforts to register or qualify or cooperate with the Holders, the Special
      Counsel and the underwriters, if any, in connection with the registration
      or qualification (or exemption from such registration or qualification) of
      such Registrable Securities for offer and sale under the securities or
      Blue Sky laws of such jurisdictions within the United States as any Holder
      or underwriter reasonably requests in writing (which request may be
      included with the Required Information); prior to any public offering of
      the Registrable Securities pursuant to the Registration Statement, use its
      reasonable commercial efforts to keep each such registration or
      qualification (or exemption therefrom) effective during the period
      provided herein with respect to the disposition of all securities covered
      by such Registration Statement in connection with such Holder's offer and
      sale of Registrable Securities pursuant to such registration or
      qualification (or exemption therefrom) and do any and all other acts or
      things reasonably necessary or advisable to enable the disposition in such
      jurisdictions of such Registrable Securities in the manner set forth in
      the relevant Registration Statement and the related Prospectus; provided
      that the Trustee will not be required to (i) qualify as a foreign entity
      or as a dealer in securities in any jurisdiction where it would not
      otherwise be required to qualify but for this Agreement or (ii) take any
      action that would subject it to general service of process or to taxation
      in any such jurisdiction where it is not then so subject.

            (j) Upon (A) the issuance by the SEC of a stop order suspending the
      effectiveness of any Registration Statement or the initiation of
      proceedings with respect to any Registration Statement under Section 8(d)
      or 8(e) of the Securities Act, (B) the occurrence of any event or the
      existence of any fact (a "MATERIAL EVENT") as a result of which any
      Registration Statement shall contain any untrue statement of a material
      fact or omit to state any material fact required to be stated therein or
      necessary to make the statements therein not misleading, or any Prospectus
      shall contain any untrue statement of a material fact or omit to state any
      material fact required to be stated therein or necessary to make the
      statements therein, in the light of the circumstances under which they
      were made, not misleading, or (C) the occurrence or existence of any
      pending

                                       7
<PAGE>

      corporate development that, in the reasonable discretion of the Trustee,
      makes it appropriate to suspend the availability of any Registration
      Statement and the related Prospectus, the Trustee shall:

                  (i) in the case of clause (B) above, subject to the next
            sentence, as promptly as practicable prepare and file, if necessary
            pursuant to applicable law, a post-effective amendment to such
            Registration Statement or a supplement to the related Prospectus or
            any document incorporated therein by reference or file any other
            required document that would be incorporated by reference into such
            Registration Statement and Prospectus so that such Registration
            Statement does not contain any untrue statement of a material fact
            or omit to state any material fact required to be stated therein or
            necessary to make the statements therein not misleading, and such
            Prospectus does not contain any untrue statement of a material fact
            or omit to state any material fact required to be stated therein or
            necessary to make the statements therein, in the light of the
            circumstances under which they were made, not misleading, as
            thereafter delivered to the purchasers of the Registrable Securities
            being sold thereunder, and, in the case of a post-effective
            amendment to a Registration Statement, subject to the next sentence,
            use its reasonable commercial efforts to cause it to be declared
            effective as promptly as practicable; and

                  (ii) give notice to the Holders and the Special Counsel, if
            any, that the availability of any Registration Statement is
            suspended (a "DEFERRAL NOTICE") and, upon receipt of any Deferral
            Notice, each Holder agrees not to sell any Registrable Securities
            pursuant to the Registration Statement until such Holder's receipt
            of copies of the supplemented or amended Prospectus provided for in
            clause (i) above, or until it is advised in writing by the Trustee
            that the Prospectus may be used, and has received copies of any
            additional or supplemental filings that are incorporated or deemed
            incorporated by reference in such Prospectus, in which case such
            Holder will use the Prospectus as so supplemented or amended in
            connection with any offering and sale of Registrable Securities
            covered thereby.

The Trustee shall use its reasonable commercial efforts to ensure that the use
of the Prospectus may be resumed (x) in the case of clause (A) above, as
promptly as is practicable, (y) in the case of clause (B) above, as soon as, in
the sole judgment of the Trustee, public disclosure of such Material Event would
not be prejudicial to or contrary to the interests of the Trust or, if necessary
to avoid unreasonable burden or expense, as soon as practicable thereafter, and
(z) in the case of clause (C) above, as soon as, in the reasonable discretion of
the Trustee, such suspension is no longer appropriate. The Trustee shall be
entitled to exercise its right under this Section 3(j) to suspend the
availability of any Registration Statement or any Prospectus (the "DEFERRAL
PERIOD").

            (k) If reasonably requested by a Holder or any underwriter
      participating in any disposition of Registrable Securities, if any, in
      writing in connection with a disposition by such Holder of Registrable
      Securities pursuant to a Registration Statement, make reasonably available
      for inspection during normal business hours by a representative for such
      Holder(s) of such Registrable Securities, any broker-dealers,

                                       8
<PAGE>

      underwriters, attorneys and accountants retained by such Holder(s), and
      any attorneys or other agents retained by a broker-dealer or underwriter
      engaged by such Holder(s), all relevant financial and other records and
      pertinent corporate documents and properties of the Trust, and cause the
      appropriate officers, directors and employees of the Trustee to make
      reasonably available for inspection during normal business hours on
      reasonable notice all relevant information reasonably requested by such
      representative for the Holder(s), or any such broker-dealers,
      underwriters, attorneys or accountants in connection with such
      disposition, in each case as is customary for similar "due diligence"
      examinations; provided that (i) the Trustee shall not be obligated to make
      available for inspection any information that, based on the reasonable
      advice of counsel to the Trustee, could subject the Trustee to the loss of
      privilege with respect thereto and (ii) such persons shall first agree in
      writing with the Trustee that any information that is reasonably
      designated by the Trustee as confidential at the time of delivery of such
      information shall be kept confidential by such persons and shall be used
      solely for the purposes of exercising rights under this Agreement, unless
      (a) disclosure of such information is required by court or administrative
      order or is necessary to respond to inquiries of regulatory authorities,
      (b) disclosure of such information is required by law (including any
      disclosure requirements pursuant to federal securities laws in connection
      with the filing of any Registration Statement or the use of any Prospectus
      referred to in this Agreement) or (c) such information becomes generally
      available to the public other than as a result of a disclosure or failure
      to safeguard by any such person; and provided further that the foregoing
      inspection and information gathering shall, to the greatest extent
      possible, be coordinated on behalf of all the Holders and the other
      parties entitled thereto by Special Counsel, if any, or another
      representative selected by a majority of Registrable Securities being sold
      by such Holders pursuant to such Registration Statement. Any person
      legally compelled or required by administrative or court order or by a
      regulatory authority to disclose any such confidential information made
      available for inspection shall provide the Trustee with prompt prior
      written notice of such requirement so that the Trustee may seek a
      protective order or other appropriate remedy.

            (l) Use best efforts to comply with all applicable rules and
      regulations of the SEC and make generally available to the Trust's
      securityholders earnings statements (which need not be audited) satisfying
      the provisions of Section 11(a) of the Securities Act and Rule 158
      thereunder (or any similar rule promulgated under the Securities Act) for
      a 12-month period commencing on the first day of the first fiscal quarter
      of the Trust commencing after the effective date of a Registration
      Statement, which statements shall be made available no later than the next
      succeeding Business Day after such statements are required to be filed
      with the SEC.

            (m) Cooperate with each Holder and the managing underwriters, if
      any, to facilitate the timely preparation and delivery of certificates
      representing Registrable Securities sold or to be sold pursuant to a
      Registration Statement, which certificates shall not bear any restrictive
      legends, and cause such Registrable Securities to be registered in such
      names as such Holder or the managing underwriters, if any, may request in
      writing at least two (2) Business Days prior to any sale of such
      Registrable Securities.

                                       9
<PAGE>

            (n) Provide a CUSIP number for all Registrable Securities covered by
      each Registration Statement not later than the effective date of such
      Registration Statement.

            (o) Cooperate and assist in any filings required to be made with the
      National Association of Securities Dealers, Inc. in connection with the
      filing or effectiveness of any Registration Statement, any post-effective
      amendment thereto or any offer or sale of Trust Units thereunder.

            (p) In the case of a proposed sale pursuant to a Registration
      Statement involving an underwritten offering, the Trustee shall enter into
      such customary agreements (including, if requested, an underwriting
      agreement in reasonably customary form) and take all such other action, if
      any, as Holders of a majority of the Registrable Securities being sold or
      any managing underwriters reasonably shall request in order to facilitate
      any disposition of the Registrable Securities pursuant to such
      Registration Statement, including, without limitation, (i) using its
      reasonable commercial efforts to cause its counsel to deliver an opinion
      or opinions in reasonably customary form, (ii) using its reasonable best
      efforts to cause its officers to execute and deliver all customary
      documents and certificates and (iii) using its reasonable best efforts to
      cause its independent public accountants to provide a comfort letter or
      letters in reasonably customary form.

            (q) Cause its officers to use their reasonable best efforts to
      support the marketing of the Registrable Securities covered by the
      Registration Statement (including, without limitation, participation in
      "road shows") taking into account the Trust's business needs.

            (r) Upon (i) the filing of any Registration Statement and (ii) the
      effectiveness of any Registration Statement, announce the same, in each
      case by press release to Reuters Economic Services and Bloomberg Business
      News.

            (s) Use its reasonable commercial efforts to cause all such
      Registrable Securities to be listed on each securities exchange or
      quotation system on which similar securities issued by the Trust are
      listed or traded.

      SECTION 4. Holder's Obligations.

      (a) Each Holder agrees that if such Holder wishes to sell Registrable
Securities pursuant to a Registration Statement and related Prospectus, it will
do so only in accordance with this Section 4 and Section 3(j) hereof. The
Trustee may require each seller of Registrable Securities as to which any
registration is being effected to furnish to the Trustee in writing such
information required in connection with such registration regarding such seller
and the distribution of such Registrable Securities as the Trustee may, from
time to time, reasonably request in writing (the "Required Information") and the
Trustee may exclude from such registration the Registrable Securities of any
seller who unreasonably fails to furnish such information within a reasonable
time after receiving such request. In addition, following the date that a
Registration Statement is declared effective, each Holder wishing to sell
Registrable Securities pursuant to a Registration Statement and related
Prospectus agrees to deliver, at least

                                       10
<PAGE>

seven (7) Business Days prior to any intended distribution of Registrable
Securities under the Registration Statement, to the Trustee any additional
Required Information as the Trustee may reasonably request so that the Trustee
may complete or amend the information required by any Registration Statement.

      (b) Each Holder agrees, by acquisition of the Registrable Securities, that
no Holder shall be entitled to sell any of such Registrable Securities pursuant
to a Registration Statement or to receive a Prospectus relating thereto unless
such Holder has furnished the Trustee with the Required Information as required
pursuant to this Section 4 and the information set forth in the next sentence.
Each Holder agrees promptly to furnish to the Trustee all information required
to be disclosed in order to make the information previously furnished to the
Trustee by such Holder not misleading and any other information regarding such
Holder and the distribution of such Registrable Securities as the Trustee may
from time to time reasonably request. Any sale of any Registrable Securities by
any Holder shall constitute a representation and warranty by such Holder that
the information relating to such Holder and its plan of distribution is as set
forth in the Prospectus delivered by such Holder in connection with such
disposition, that such Prospectus does not as of the time of such sale contain
any untrue statement of a material fact relating to or provided by such Holder
or its plan of distribution and that such Prospectus does not as of the time of
such sale omit to state any material fact relating to or provided by such Holder
or its plan of distribution necessary to make the statements in such Prospectus,
in the light of the circumstances under which they were made, not misleading.

      SECTION 5. Registration Expenses. The Company shall bear all out-of-pocket
fees and expenses incurred in connection with the performance by the Trustee of
its obligations under Sections 2 and 3 of this Agreement whether or not any
Registration Statement is declared effective. Such fees and expenses shall
include, without limitation, (i) all registration and filing fees (including,
without limitation, fees and expenses (x) with respect to filings required to be
made with the National Association of Securities Dealers, Inc. and (y) of
compliance with federal and state securities or Blue Sky laws (including,
without limitation, reasonable fees and disbursements of the Special Counsel, if
any, in connection with Blue Sky qualifications of the Registrable Securities
under the laws of such jurisdictions as Holders of a majority of the Registrable
Securities being sold pursuant to a Registration Statement may designate)), (ii)
printing expenses (including, without limitation, expenses of printing
certificates for Registrable Securities in a form eligible for deposit with The
Depository Trust Company), (iii) duplication expenses relating to copies of any
Registration Statement or Prospectus delivered to any Holders hereunder, (iv)
fees and disbursements of counsel for the Trustee and the Special Counsel, if
any, in connection with any Registration Statement, (v) fees of accountants for
consents and cold comfort and (vi) the fees and expenses incurred in connection
with the listing by the Trustee of the Registrable Securities on any securities
exchange on which similar securities of the Trust are then listed. However, the
Trustee shall pay the internal expenses of the Trustee (including, without
limitation, all salaries and expenses of officers and employees performing legal
or accounting duties), the expense of any annual audit and the other fees and
expenses of the accountants for the Trust not covered by clause (v) of the
preceding sentence, other than any expense that would not have otherwise been
incurred but for the fact of the filing of the registration statement or the
timing thereof, the fees and expenses of any person, including special experts,
retained by the Trustee and the fees and expenses of any transfer agent for the
Registrable Securities. Notwithstanding the provisions of this Section 5, each
seller of

                                       11
<PAGE>

Registrable Securities shall pay its own selling expenses, including any
underwriting discount and commissions, all registration expenses to the extent
required by applicable law and, except as otherwise provided herein, fees and
expenses of counsel.

      SECTION 6. Indemnification and Contribution.

      (a) Indemnification by the Trustee. The Trustee agrees to indemnify and
hold harmless each Holder and each person, if any, who controls any Holder
within the meaning of either Section 15 of the Securities Act or Section 20 of
the Exchange Act, from and against any and all losses, claims, damages and
liabilities (including, without limitation, any reasonable legal or other
expenses reasonably incurred in connection with defending or investigating any
such action or claim) ("EXPENSES") caused by any untrue statement or alleged
untrue statement of a material fact contained in any Registration Statement or
any amendment thereof, any preliminary prospectus or the Prospectus (as amended
or supplemented if the Trustee shall have furnished any amendments or
supplements thereto), caused by any omission or alleged omission to state
therein a material fact required to be stated therein or necessary to make the
statements therein not misleading, but only with respect to written information
relating to the Trustee furnished by or on behalf of the Trustee specifically
for inclusion in the documents referred to in the foregoing indemnity. In
connection with any underwritten offering pursuant to Section 8, the Trustee
will also agree to indemnify the underwriters, if any, their officers and
directors and each person who controls such underwriters (within the meaning of
the Securities Act and the Exchange Act) on terms and conditions similar to
those set forth herein with respect to the indemnification of the Holders, if
requested in connection with any Registration Statement, such indemnification to
be set forth in any underwriting agreement to be entered into by the Trustee
with such underwriter(s).

      (b) Indemnification by the Company. The Company shall indemnify and hold
harmless the Trustee and any agents thereof, individually and as trustee, as the
case may be, from and against any Expenses (excluding, however, any taxes, fees
and other charges payable by the Trustee on, based on or measured by any fees,
commissions or compensation received by the Trustee for its services under this
Agreement) to which such Trustee or any agent thereof, may become subject, under
or with respect to the Securities Act, the Exchange Act, any other federal or
state securities law or otherwise, insofar as such Expenses are caused by an
untrue statement or alleged untrue statement of a material fact contained in, or
an omission or alleged omission of a material fact from, (i) any Registration
Statement, the Prospectus, or any amendment or supplement thereto, (ii) any
other filing, report or other action taken with respect to the Securities Act,
the Exchange Act or any other Federal or state securities law, the listing of
the Trust Units on the New York Stock Exchange or another national securities
exchange or the quotation of the Trust Units on NASDAQ; provided, however, that
the Company shall not be liable to and shall not indemnify the Trustee or any
agents thereof, individually or as trustee, as the case may be, in any such case
under the preceding clause (i) of this Section 6(b) to the extent that any such
Expense arises out of, is based upon or is connected with information relating
to the Trustee prepared or furnished by the Trustee expressly for use in any
Registration Statement, the Prospectus or any amendment or supplement thereof;
and provided, further, that the Company shall not be liable to the Trustee or
any agents thereof, individually or as trustee, as the case may be, in any such
case under the preceding clause (ii) of this Section 6(b) to the extent that any
such Expense arises out of, is based upon or is connected with information
relating to the Trustee

                                       12
<PAGE>

prepared or furnished by the Trustee and the Trustee is found liable. Subject to
Section 6(d) of this Agreement, the Company shall reimburse the Trustee and any
agents thereof for any legal or other expenses reasonably incurred by the
Trustee in connection with the investigation or defense of any Expenses with
respect to which the Trustee or any agent thereof is entitled to indemnity by
the Company under this Agreement.

      (c) Conduct of Indemnification Proceedings. In case any proceeding
(including any governmental investigation) shall be instituted involving any
person in respect of which indemnity may be sought pursuant to Section 6(a) or
6(b) hereof, such person (the "INDEMNIFIED PARTY") shall promptly notify the
person against whom such indemnity may be sought (the "INDEMNIFYING PARTY") in
writing and the indemnifying party, upon request of the indemnified party, shall
retain counsel reasonably satisfactory to the indemnified party to represent the
indemnified party and any others the indemnifying party may designate in such
proceeding and shall pay the reasonable fees and disbursements of such counsel
related to such proceeding. In any such proceeding, any indemnified party shall
have the right to retain its own counsel, but the fees and expenses of such
counsel shall be at the expense of such indemnified party unless (i) the
indemnifying party and the indemnified party shall have mutually agreed to the
retention of such counsel or (ii) the named parties to any such proceeding
(including any impleaded parties) include both the indemnifying party and the
indemnified party and representation of both parties by the same counsel would
be inappropriate due to actual or potential differing interests between them,
other than solely by virtue of the rights and obligations of the indemnifying
party and the indemnified party under this Section 6. It is understood that the
indemnifying party shall not, in respect of the legal expenses of any
indemnified party in connection with any proceeding or related proceedings in
the same jurisdiction, be liable for the fees and expenses of more than one
separate firm (in addition to any local counsel) for all such indemnified
parties and that all such fees and expenses shall be reimbursed as they are
incurred. Such firm shall be designated in writing by, in the case of parties
indemnified pursuant to Section 6(a), the Holders of a majority of the
Registrable Securities covered by the Registration Statement held by Holders
that are indemnified parties pursuant to Section 6(a) and, in the case of
parties indemnified pursuant to Section 6(b), the Trustee. The indemnifying
party shall not be liable for any settlement of any proceeding effected without
its written consent, but if settled with such consent or if there be a final,
non-appealable judgment for the plaintiff, the indemnifying party agrees to
indemnify the indemnified party from and against any loss or liability by reason
of such settlement or judgment. No indemnifying party shall, without the prior
written consent of the indemnified party, effect any settlement of any pending
or threatened proceeding in respect of which any indemnified party is or could
have been a party and indemnity could have been sought hereunder by such
indemnified party, unless such settlement includes an unconditional release of
such indemnified party from all liability on claims that are the subject matter
of such proceeding.

      (d) Contribution. To the extent that the indemnification provided for in
Section 6(a) or 6(b) is unavailable to an indemnified party or insufficient in
respect of any losses, claims, damages or liabilities referred to therein, then
each indemnifying party under such paragraph, in lieu of indemnifying such
indemnified party thereunder, shall contribute to the amount paid or payable by
such indemnified party as a result of such losses, claims, damages or
liabilities (i) in such proportion as is appropriate to reflect the relative
benefits received by the indemnifying party or parties on the one hand and the
indemnified party or parties on the other hand or (ii) if the allocation
provided by clause (i) above is not permitted by applicable law, in such
proportion

                                       13
<PAGE>

as is appropriate to reflect not only the relative benefits referred to in
clause (i) above but also the relative fault of the indemnifying party or
parties on the one hand and of the indemnified party or parties on the other
hand in connection with the statements or omissions that resulted in such
losses, claims, damages or liabilities, as well as any other relevant equitable
considerations. The relative fault of the Holders on the one hand and the
Trustee on the other hand shall be determined by reference to, among other
things, whether the untrue or alleged untrue statement of a material fact or the
omission or alleged omission to state a material fact relates to information
supplied by the Holders or by the Trustee, and the parties' relative intent,
knowledge, access to information and opportunity to correct or prevent such
statement or omission. The Holders' respective obligations to contribute
pursuant to this Section 6 are several in proportion to the respective number of
Registrable Securities they have sold pursuant to a Registration Statement, and
not joint.

      The parties hereto agree that it would not be just and equitable if
contribution pursuant to this Section 6(d) were determined by pro rata
allocation or by any other method of allocation that does not take into account
the equitable considerations referred to in the immediately preceding paragraph.
The amount paid or payable by an indemnified party as a result of the losses,
claims, damages or liabilities referred to in the immediately preceding
paragraph shall be deemed to include, subject to the limitations set forth
above, any legal or other expenses reasonably incurred by such indemnified party
in connection with investigating or defending any such action or claim. No
person guilty of fraudulent misrepresentation (within the meaning of Section 11
(f) of the Securities Act) shall be entitled to contribution from any person who
was not guilty of such fraudulent misrepresentation.

      (e) The remedies provided for in this Section 6 are not exclusive and
shall not limit any rights or remedies which may otherwise be available to an
indemnified party at law or in equity, hereunder or otherwise.

      (f) The indemnity and contribution provisions contained in this Section 6
shall remain operative and in full force and effect regardless of (i) any
termination of this Agreement, (ii) any investigation made by or on behalf of
any Holder, any person controlling any Holder or any affiliate of any Holder or
by or on behalf of the Trustee, its officers or directors or any person
controlling the Trustee and (iii) the sale of any Registrable Securities by any
Holder.

      SECTION 7. Information Requirements. The Trustee covenants that, if at any
time before the end of the Effective Period the Trust is not subject to the
reporting requirements of the Exchange Act, it will cooperate with any Holder
and take such further reasonable action as any Holder may reasonably request in
writing (including, without limitation, making such reasonable representations
as any such Holder may reasonably request), all to the extent required from time
to time to enable such Holder to sell Registrable Securities without
registration under the Securities Act within the limitation of the exemptions
provided by Rule 144 and Rule 144A under the Securities Act and customarily
taken in connection with sales pursuant to such exemptions. Upon the written
request of any Holder, the Trustee shall deliver to such Holder a written
statement as to whether the Trust has complied with such filing requirements.
Notwithstanding the foregoing, nothing in this Section 7 shall be deemed to
require the Trustee to register any of the Trust's securities under any section
of the Exchange Act.

                                       14
<PAGE>

      SECTION 8. Underwritten Registrations. The Holders of Registrable
Securities covered by any Registration Statement who desire to do so may sell
such Registrable Securities to an underwriter in an underwritten offering for
reoffering to the public. If any of the Registrable Securities covered by any
Registration Statement are to be sold in an underwritten offering, the
investment banker or investment bankers and manager or managers that will
administer the offering will be selected by the Holders of a majority of such
Registrable Securities included in such offering, subject to the consent of the
Trustee (which shall not be unreasonably withheld or delayed), and such Holders
shall be responsible for all underwriting commissions and discounts and any
transfer taxes in connection therewith. No person may participate in any
underwritten registration hereunder unless such person (i) agrees to sell such
person's Registrable Securities on the basis reasonably provided in any
underwriting arrangements approved by the persons entitled hereunder to approve
such arrangements and (ii) completes and executes all questionnaires, powers of
attorney, indemnities, underwriting agreements and other documents reasonably
required under the terms of such underwriting arrangements.

      SECTION 9. Miscellaneous.

      (a) Amendments and Waivers. The provisions of this Agreement, including
the provisions of this sentence, may not be amended, modified or supplemented,
and waivers or consents to departures from the provisions hereof may not be
given, without the written consent of the Trustee and Holders of a majority of
Registrable Securities. Notwithstanding the foregoing, a waiver or consent to
depart from the provisions hereof with respect to a matter that relates
exclusively to the rights of Holders whose securities are being sold pursuant to
a Registration Statement and that does not directly or indirectly affect the
rights of other Holders may be given by Holders of at least a majority of the
Registrable Securities being sold by such Holders pursuant to such Registration
Statement; provided that the provisions of this sentence may not be amended,
modified or supplemented except in accordance with the provisions of the
immediately preceding sentence. Notwithstanding the foregoing, this Agreement
may be amended by written agreement signed by the Trustee, without the consent
of the Holders of Registrable Securities, to cure any ambiguity or to correct or
supplement any provision contained herein that may be defective or inconsistent
with any other provision contained herein, or to make such other provisions in
regard to matters or questions arising under this Agreement that shall not
adversely affect the interests of the Holders of Registrable Securities. Each
Holder of Registrable Securities outstanding at the time of any such amendment,
modification, supplement, waiver or consent or thereafter shall be bound by any
such amendment, modification, supplement, waiver or consent effected pursuant to
this Section 9(a), whether or not any notice, writing or marking indicating such
amendment, modification, supplement, waiver or consent appears on the
Registrable Securities or is delivered to such Holder.

      (b) Notices. All notices and other communications provided for or
permitted hereunder shall be made in writing by hand delivery, by facsimile, by
courier guaranteeing overnight delivery or by first-class mail, return receipt
requested, and shall be deemed given (i) when made, if made by hand delivery,
(ii) upon confirmation, if made by facsimile, (iii) one (1) Business Day after
being deposited with such courier, if made by overnight courier or (iv) on the
date indicated on the notice of receipt, if made by first-class mail, to the
parties as follows:

                                       15
<PAGE>

                 (i)  if to a Holder, at the most current address given by such
            Holder to the Trustee;

                 (ii)  if to the Trustee, to:

                       Bank of America, N.A.
                       Trust Division
                       Royalty Trust Group
                       901 Main Street, 17th Floor
                       Dallas, Texas 75202
                       Attention: Ron E. Hooper
                       Fax: (214) 209-2431

                       with a copy to:

                       Thompson & Knight L.L.P.
                       1700 Pacific Avenue
                       Suite 3300
                       Dallas, Texas 75201
                       Attention:  Amy R. Curtis
                       Fax: (214) 999-1564

                 (iii) if to the Company, to:

                       Burlington Resources Inc.
                       717 Texas Avenue
                       Suite 2100
                       Houston, Texas 77002
                       Attention: Treasurer
                       Fax: (713) 624-3745

                       with a copy to:

                       Andrews Kurth LLP
                       600 Travis Street
                       Suite 4200
                       Houston, Texas  77002
                       Attention: G. Michael O'Leary
                       Fax: (713) 220-4285

or to such other address as such person may have furnished to the other persons
identified in this Section 9(b) in writing in accordance herewith.

      (c) Approval of Holders. Whenever the consent or approval of Holders of a
specified percentage of Registrable Securities is required hereunder,
Registrable Securities held by the Trust or its affiliates (as such term is
defined in Rule 405 under the Securities Act) (other than the Company or
subsequent Holders if such Holders are deemed to be such affiliates solely by

                                       16
<PAGE>

reason of their holdings of such Registrable Securities) shall not be counted in
determining whether such consent or approval was given by the Holders of such
required percentage.

      (d) Successors and Transferees. Any person or group of persons who
purchases any Registrable Securities from the Company shall be deemed, for
purposes of this Agreement, to be a transferee of the Company, but if and only
if such person or group (i) agrees to be designated as a transferee, (ii) is
specifically designated as a transferee in writing by the Company to the Trustee
and (iii) in the case of a group such group shall collectively constitute a
Transferee for purposes of this Agreement (including without limitation, for
purposes of exercising any Demand Registration right transferred by the Company
to such group (a "TRANSFEREE"). This Agreement shall inure to the benefit of and
be binding upon such Transferees and shall inure to the benefit of and be
binding upon each such Transferees, provided that nothing herein shall be deemed
to permit any assignment, transfer or other disposition of Registrable
Securities in violation of the terms thereof. If the Company designates any
person as a Transferee in accordance with this Section 9(d), then the
Registrable Securities acquired by such Transferee shall be held subject to all
of the terms of this Agreement, and by taking and holding such Registrable
Securities, such person shall be conclusively deemed to have agreed to be bound
by and to perform all of the terms and provisions of this Agreement and such
person shall be entitled to receive the benefits hereof.

      (e) Counterparts. This Agreement may be executed in any number of
counterparts and by the parties hereto in separate counterparts, each of which
when so executed shall be deemed to be original and all of which taken together
shall constitute one and the same agreement.

      (f) Headings. The headings in this Agreement are for convenience of
reference only and shall not limit or otherwise affect the meaning hereof.

      (g) Governing Law. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF TEXAS.

      (h) Severability. If any term provision, covenant or restriction of this
Agreement is held to be invalid, illegal, void or unenforceable, the remainder
of the terms, provisions, covenants and restrictions set forth herein shall
remain in full force and effect and shall in no way be affected, impaired or
invalidated thereby, and the parties hereto shall use their reasonable best
efforts to find and employ an alternative means to achieve the same or
substantially the same result as that contemplated by such term, provision,
covenant or restriction, it being intended that all of the rights and privileges
of the parties shall be enforceable to the fullest extent permitted by law.

      (i) Entire Agreement. This Agreement is intended by the parties as a final
expression of their agreement and is intended to be a complete and exclusive
statement of the agreement and understanding of the parties hereto in respect of
the subject matter contained herein and the registration rights granted by the
Trustee with respect to the Registrable Securities. There are no restrictions,
promises, warranties or undertakings, other than those set forth or referred to
herein, with respect to the registration rights granted by the Trustee with
respect to the Registrable Securities. This Agreement supersedes all prior
agreements and undertakings among the parties

                                       17
<PAGE>

with respect to such registration rights. No party hereto shall have any rights,
duties or obligations other than those specifically set forth in this Agreement.

      (j) Termination. This Agreement and the obligations of the parties
hereunder shall terminate upon the end of the Effective Period, except for any
liabilities or obligations under Section 4, 5 or 6 hereof, each of which shall
remain in effect in accordance with its terms.

      (k) Specific Enforcement; Venue. The parties hereto acknowledge and agree
that each would be irreparably damaged if any of the provisions of this
Agreement are not performed by the other in accordance with their specific terms
or are otherwise breached. It is accordingly agreed that each party shall be
entitled to seek an injunction or injunctions to prevent breaches of this
Agreement by the other and to enforce this Agreement and the terms and
provisions hereof specifically against the other, in addition to any other
remedy to which such aggrieved party may be entitled at law or in equity. Any
action or proceeding seeking to enforce any provision of, or based on any rights
arising out of, this Agreement may be brought against any of the parties in the
Federal AND TEXAS STATE COURTS SITTING IN DALLAS, DALLAS COUNTY, TEXAS OR
HOUSTON, HARRIS COUNTY, TEXAS and each of the parties consents to the
jurisdiction of such courts (and of the appropriate appellate courts) in any
such action or proceeding and waives any objection to venue laid therein.
Process in any action or proceeding referred to in the preceding sentence may be
served on any party anywhere in the world.

                                       18
<PAGE>

                  IN WITNESS WHEREOF, the parties have executed this Agreement
            as of the date first written above.

                                       BURLINGTON RESOURCES INC.

                                       By: /s/ Steven J. Shapiro
                                           -------------------------------------
                                           Name: Steven J. Shapiro
                                           Title: Executive Vice President
                                           and Chief Financial Officer

                                       BANK OF AMERICA, N.A., TRUSTEE FOR
                                       PERMIAN BASIN ROYALTY TRUST

                                       By: /s/ Ron E. Hooper
                                           -------------------------------------
                                           Name: Ron E. Hooper
                                           Title: Senior Vice President

                                       19

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00069-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00069-of-00352.parquet"}]]