Document:

<PAGE>   1

                                                                   EXHIBIT 10.11

                                 August 14, 2000

Contango Oil & Gas Company
ATTN:  Mr. Ken Peak
3700 Buffalo Speedway, Suite 960
Houston, TX  77098

         RE:  AGREEMENT DATED EFFECTIVE SEPTEMBER 1, 1999, BY AND BETWEEN
              CONTANGO OIL & GAS COMPANY AND JUNEAU EXPLORATION, L.L.C.
              (THE "AGREEMENT," WITH ALL CAPITALIZED TERMS USED BUT NOT DEFINED
              HEREIN BEING AS DEFINED IN SUCH AGREEMENT)

Gentlemen:

The purpose of this letter is to formally amend and modify certain terms and
conditions of the subject Agreement as hereinafter set forth.

As of the Effective Date of the Agreement, the Agreement shall be amended as
follows:

1.       All existing references to "Juneau Exploration, L.L.C." shall be
         amended to "Juneau Exploration Company, LLC."

2.       SECTION 1.5 OVERHEAD AND OTHER COSTS. "Allocable Seismic Costs" shall
         be redefined as "that portion of the seismic costs incurred by JEX in
         the acquisition and interpretation of seismic data allocated to such
         Prospect in a manner determined by JEX, which shall include, but not be
         limited to, the cost and expense of the seismic data (including
         reproduction charges for seismic tape deliveries), synthetic
         seismograms, digital logs used for synthetic seismograms and third
         party charges for seismic modeling and reprocessing."

Effective as of August 1, 2000 ("Revised Effective Date"), the Agreement shall
be amended as follows:

1.       SECTION 2.2 OVERRIDING ROYALTY INTEREST shall be deleted in its
         entirety and replaced with, "Upon commencement of operations for the
         drilling of the initial well drilled pursuant to this Agreement on each
         Prospect in which Contango has elected or is obligated to participate,
         JEX shall be entitled to an assignment or reservation of an overriding
         royalty interest equal to 3-1/3% of Contango's working interest in each
         Prospect, which overriding royalty interest shall be inclusive of and
         shall bear the sum of any and all other overriding royalty interests
         burdening Contango's interest in such Prospect that were conveyed, or
         required to be conveyed, to other persons or entities who were employed
         by JEX, or engaged as consultants to JEX, to assist in JEX's
         generation, screening, sourcing and/or acquisition of such Prospect
         (the "JEX ORRI"). An example calculation of the JEX ORRI is set forth
         on Schedule 2.2 attached hereto."

<PAGE>   2

Amendment to Contango Agreement
August 14, 2000
Page Two

2.       SECTION 2.3 BACK-IN AFTER PROGRAM PAYOUT shall be deleted in its
         entirety and replaced with, "Section 2.3 BACK-IN AFTER PROSPECT PAYOUT.
         The term "Prospect Payout" as used herein shall mean, with regard to
         each Prospect, 9:00 a.m. on the first day of the calendar month
         following the calendar month during which Contango's share of all
         revenues from the sale of oil, gas and other minerals produced from a
         Prospect, net of Contango's share of (i) all royalties, overriding
         royalties (including the JEX ORRI) and other similar lease burdens,
         (ii) severance taxes, production taxes, excise taxes and other similar
         taxes levied on or measured by such production and (iii) lease
         operating expenses attributable to such Prospect first equals or
         exceeds Contango's share of all CAPEX expended for the origination and
         acquisition of such Prospect and the conduct of exploration,
         development and production operations thereon. At Prospect Payout, JEX
         shall be entitled to an assignment or automatic reversion of an
         undivided twenty-five percent (25%) of Contango's working interest in
         the Prospect (the "JEX Back-in"). Contango shall maintain books and
         records tracking the status of Prospect Payout with respect to each
         Prospect and shall issue quarterly statements to JEX regarding the
         status of Prospect Payout for each Prospect. Simultaneous with JEX's
         assignment to Contango of Contango's interest in each Prospect, both
         parties shall execute a mutually acceptable form of memorandum of
         agreement and record same in the appropriate records of any parish or
         county within which the Prospect is located (or in the nearest adjacent
         parish or county in the case of oil and gas leases in the Outer
         Continental Shelf) to give public notice of the JEX Back-in."

3.       SECTION 2.5 OPTIONS and SECTION 2.6 ADJUSTMENT OF OPTION SHARES AND
         EXERCISE PRICE shall both be deleted in their entirety.

4.       SECTION 4.1 TERM shall be deleted in its entirety and replaced with,
         "This Agreement shall commence on the date hereof (the "Effective
         Date") and shall remain in effect until terminated by (a) Contango upon
         thirty (30) day's prior written notice to JEX or (b) JEX upon one
         hundred eighty (180) day's prior written notice to Contango, unless
         Contango is in default under this Agreement in which case the notice
         period shall be thirty (30) days; provided, however, that this
         Agreement shall remain in effect with respect to any transaction(s)
         entered into prior to the effective date of the termination until both
         Parties have fulfilled their obligations with respect to such
         transaction(s)."

5.       Add SECTION 4.12 FINAL PROGRAM PAYOUT PROPERTIES. Contango and JEX
         agree that only those Prospects set forth on Schedule 4.12 attached
         hereto ("Final Program Payout Properties") shall be included in Program
         Payout under the terms of this Agreement, and no additional Prospects
         shall ever be added thereto."

The parties hereby agree that (i) the above stated modifications and revisions
("Revisions") will apply to any and all future wells drilled under the
Agreement, as amended, and (ii) such Revisions will likewise govern any and all
future wells drilled pursuant to that certain Exploration and Operations
Agreement dated March 21, 2000, by and between Mestena, Inc. and Juneau
Exploration Company, LLC ("Mestena Agreement"), beginning with the Guilita No.
3. Well; provided, however, notwithstanding the foregoing, it is understood and
agreed that Lease "1" #67, Guilita #1, Guilita #2 and Cepres #1 wells, being the
obligatory wells under Phase I of the Mestena Agreement, shall in no way be
affected or governed by such Revisions.

<PAGE>   3

Amendment to Contango Agreement
August 14, 2000
Page Three

Except as expressly modified by this letter, all other terms and conditions of
the Agreement shall remain unchanged and in full force and effect.

If you accept and agree to the terms of this letter, please sign in the space
provided below and return one (1) original to the undersigned at your earliest
opportunity.

Very truly yours,

/s/  LINDA G. FERSZT

Linda G. Ferszt
Vice President - Land

Cc:  Mr. John B. Juneau

AGREED TO AND ACCEPTED
this 18 th day of August, 2000.

CONTANGO OIL & GAS COMPANY

BY:  /s/ KENNETH R. PEAK
    -------------------------------
         Kenneth R. Peak
         President

<PAGE>   4

                                  SCHEDULE 4.12

                         FINAL PROGRAM PAYOUT PROPERTIES

                           Buena Vista Hills, LLC, CA

                       Eugune Island Block 28, Offshore LA

                       Brazos Area Block 436, Offshore TX

              Dominion Acquisition, Colorado & Wharton Counties, TX

           Point Six, Point Five & Weanie Prospects, Goliad County, TX

                         Needville, Fort Bend County, TX

          Mestena Ranch, Phase I only (Lse "1" #67, Guilita #1 & #2 and
                  Cepres #1 Wells), Jim Hogg & Brooks Cos., TX<PAGE>

                                                                Exhibit 10(o)(v)

           FIRST AMENDMENT TO AMENDED AND RESTATED LICENSE AGREEMENT
                                   (Canada)

This First Amendment to Amended and Restated License Agreement is dated as of
June 1, 2000, between RadioShack Corporation (formerly Tandy Corporation)
("RadioShack") and InterTAN Canada Ltd. ("ITC").

WHEREAS, RadioShack and ITC entered into that certain Amended and Restated
License Agreement on January 25, 1999 (the "Agreement");

WHEREAS, RadioShack has been requested by ITC to approve a specific form of
sublicense of RadioShack-owned intellectual property from ITC to a third party
corporation.

NOW, THEREFORE, for good and valuable consideration, the receipt and sufficiency
of which are hereby acknowledged, it is agreed as follows:

1.  A new provision, designated as paragraph 3A., shall be added to the
Agreement immediately following paragraph 3 thereof, and shall be as follows:

"Attached hereto and made a part of this Agreement is a new Addendum A which
                                                            ----------
sets forth the terms and conditions relating specifically to the authorized
sublicense from ITC to Chapters Online Inc. regarding certain intellectual
property rights owned by RadioShack through one or more affiliated entities."

2.  Every reference in the Agreement to Tandy Corporation (or Tandy) shall be
deemed to be a reference to RadioShack Corporation (or RadioShack).

3.  All other terms and conditions of the Agreement shall remain unchanged and
in full force and effect.

IN WITNESS WHEREOF, the parties hereto have executed this First Amendment to be
effective as of the day and year first above written.

                                 RADIOSHACK CORPORATION

                                 By: /s/ Mark C. Hill
                                     ----------------
                                 Title:  Senior Vice President, Corporate
                                 Secretary and General Counsel

                                 INTERTAN CANADA LTD.

                                 By:  /s/ James G. Gingerich
                                      ----------------------
                                 Title:  Vice President

<PAGE>

                                                                Exhibit 10(o)(v)
                                   Addendum A

            InterTAN Canada Ltd. Sublicense to Chapters Online Inc.

General Statement
-----------------

ITC has, as of the date hereof, entered into with Chapters Online Inc.
("Chapters") that certain Electronic Commerce Strategic Alliance Agreement (the
"ITC/Chapters Agreement").

The ITC/Chapters Agreement contemplates the grant of certain sublicense rights
from ITC to Chapters relating to the use of certain intellectual property rights
owned by RadioShack (through one or more of its affiliated entities) (the
"RadioShack Marks") and licensed from RadioShack to ITC under the Amended and
Restated License Agreement dated January 25, 1999 (as hereby amended) between
such parties (the "Agreement").  RadioShack is willing to authorize the
contemplated sublicense from ITC to Chapters on the terms and conditions as
specified below, which shall each be in addition to any of the terms and
conditions of the Agreement.  Any capitalized term used herein which is not
otherwise defined shall have the meaning as set forth in the Agreement.

Sublicense Terms and Conditions
-------------------------------

1.  ITC is hereby authorized to grant to Chapters a sublicense to use the
    RadioShack Marks as contemplated under the ITC/Chapters Agreement, the form
    and content of which has been approved by RadioShack. ITC agrees to use its
    best efforts to police Chapter's use of the RadioShack Marks consistent with
    its current obligations under the Agreement.

2.  ITC shall have no rights of further sublicense to any party other than
    Chapters. ITC shall have no right to assign its interest under the
    ITC/Chapters Agreement, nor shall ITC permit Chapters to assign its rights
    under the ITC/Chapters Agreement, unless and until the prior written consent
    of RadioShack is obtained. RadioShack may withhold such consent, in either
    event, with or without cause in its sole discretion.

3.  As contemplated under the ITC/Chapters Agreement, any time ITC and Chapters
    determine in the future to jointly make decisions regarding, among other
    things, the use of product tagging or labeling, graphical depictions,
    taglines, promotional materials, etc., which involve in any manner the use
    of a RadioShack Mark, ITC shall seek the prior written approval of
    RadioShack, unless it is clear to ITC under all of the relevant
    circumstances, that such proposed usage of any RadioShack Mark is in full
    accordance with RadioShack's then current Graphics Standards Manual and the
    Agreement. In the event ITC is required to obtain RadioShack's prior written
    approval, RadioShack will respond to ITC in a prompt manner, which in any
    event will not exceed three (3) business days after RadioShack's receipt of
    ITC's written request for such approval.

4.  RadioShack shall have the right to audit such books and records of ITC from
    time to time upon reasonable request and prior notice, relating to (i) the
    performance of ITC under the ITC/Chapters Agreement with respect to ITC's
    obligations thereunder to prevent the
<PAGE>

                                                                Exhibit 10(o)(v)

    shipment by ITC of any consumer electronics products (whether private label
    or nationally branded) from Canada into the United States, including in the
    District of Columbia, Puerto Rico and the U.S. Virgin Islands; (ii) the
    gross sales recorded by ITC as a result of the transactions contemplated
    under the ITC/Chapters Agreement; and (iii) the proper usage of the
    RadioShack Marks in ITC's advertising and packaging.

5.  RadioShack may revoke ITC's right to sublicense the RadioShack Marks to
    Chapters at any time, with immediate effect and without any liability
    therefor in any manner whatsoever, upon the occurrence of the following:

    (i)  RadioShack's discovery that consumer electronic product has been or is
         being shipped by ITC into the territories identified in 4(i) above in
         violation of the terms of the ITC/Chapters Agreement;

    (ii) RadioShack's discovery of any under-reporting by ITC of its gross sales
         generated under the ITC/Chapters Agreement; or

   (iii) ITC permits the persistence of an uncured breach, either by ITC or by
         Chapters, under the ITC/Chapters Agreement which directly or indirectly
         relates to or has an effect on any RadioShack Mark as determined in
         RadioShack's sole discretion, acting reasonably.

6.  Any breach by ITC of the terms and conditions of this Addendum A may, in
                                                          ----------
    RadioShack's sole discretion, be deemed to constitute a breach of the
    Agreement.

7.  ITC agrees to further indemnify and hold harmless RadioShack and those other
    entities or persons identified in Section 26 of the Agreement, to the
    fullest extent provided in the indemnity provisions of Section 26 of the
    Agreement, for any breach by Chapters of any provisions of the ITC/Chapters
    Agreement.

8.  To clarify the understanding and intentions of RadioShack and ITC, it is
    agreed that the gross sales generated by ITC under the ITC/Chapters
    Agreement shall be subject to the royalty payment contemplated in Section 5
    of the Agreement.

This Addendum A is dated as of June 1, 2000.
     ----------

RADIOSHACK CORPORATION                  INTERTAN CANADA LTD.

By: /s/ Mark C. Hill                    By: /s/ James G. Gingerich
    ----------------                        ----------------------
Title: Senior Vice President,           Title: Vice President
       Corporate Secretary and
       General Counsel

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