Document:

<Page>

                                                         Exhibits 4.12 And 10.21

                     AMENDMENT TO RESTATED CREDIT AGREEMENT

     THIS AMENDMENT TO RESTATED CREDIT AGREEMENT (hereinafter referred to as the
"Amendment") executed as of the 26th day of April, 2002, by and between EXCO
RESOURCES, INC., a Texas corporation ("EXCO") and EXCO OPERATING, LP, a Delaware
limited partnership ("Operating") (EXCO and Operating are hereinafter
collectively referred to as "Borrowers" and individually as a "Borrower") and
BANK ONE, NA, a national banking association ("Bank One"), and each of the
financial institutions which is a party thereto (as evidenced by the signature
pages to the Agreement) or which may from time to time become a party hereto
pursuant to the provisions of Section 28 thereof or any successor or assignee
thereof (hereinafter collectively referred to as "Lenders", and individually,
"Lender") and Bank One, as Administrative Agent (the "Agent") and BNP Paribas,
as Syndication Agent, and The Bank of Nova Scotia, as Documentation Agent and
Banc One Capital Markets, Inc., as Lead Arranger and Bookrunner ("Arranger").

                                   WITNESSETH:

     WHEREAS, as of April 26, 2001, EXCO, as Borrower, the Lenders and the Agent
entered into a Credit Agreement pursuant to which the Lenders made available
to the Borrowers certain credit facilities in the form therein described; and

     WHEREAS, as of December 18, 2001, Borrowers, Lenders and Agent entered into
a Restated Credit Agreement (the "Credit Agreement"); and

     WHEREAS, the Borrowers have requested that the Lenders agree to make
certain additional amendments to the Credit Agreement and the Lenders, together
with certain additional financial institutions who shall become a party to the
Credit Agreement at the Amendment Effective Date (as hereinafter defined), have
agreed to do so on the terms and conditions hereinafter set forth.

     NOW, THEREFORE, the parties agree to amend the Credit Agreement as follows:

     1.   Unless otherwise defined herein all defined terms used herein shall
have the same meaning as ascribed to such terms in the Credit Agreement.

     2.   The Lenders have agreed among themselves to reallocate their
respective Commitments and to allow Fleet National Bank and Toronto Dominion
(Texas), Inc. to acquire an interest in the Commitments and the Loans. After
such reallocation of the Commitments, the Lenders shall own the Revolving
Commitment Percentages set forth on the signature pages hereto at the Amendment
Effective Date. Each Lender shall surrender its existing Note and be issued a
new Note in a face amount equal to each Lender's Revolving Commitment Percentage
times $124,000,000. Each said Note to be in the form of Exhibit "B" to the
Credit Agreement with appropriate insertions.

<Page>

     3.   As of the Amendment Effective Date, the Borrowing Base shall be
$65,000,000 until redetermined pursuant to the provisions of Section 7(b) of the
Credit Agreement.

     4.   Except to the extent its provisions are specifically amended, modified
or superseded by this Amendment, the representations, warranties and affirmative
and negative covenants of the Borrowers contained in the Credit Agreement are
incorporated herein by reference for all purposes as if copied herein in full.
The Borrowers hereby restate and reaffirm each and every term and provision of
the Credit Agreement, as amended, including, without limitation, all
representations, warranties and affirmative and negative covenants. Except to
the extent its provisions are specifically amended, modified or superseded by
this Amendment, the Credit Agreement, as amended, and all terms and provisions
thereof shall remain in full force and effect, and the same in all respects are
confirmed and approved by the Borrowers and the Lenders.

     5.   This Amendment shall be effective as of the date first above written,
but only upon the satisfaction of the conditions precedent set forth in
Paragraph 6 hereof.

     6.   The obligations of Lenders under this Amendment shall be subject to
the following conditions precedent:

          (a)  EXECUTION AND DELIVERY. The Borrowers shall have executed and
     delivered this Amendment, and other required documents, all in form and
     substance satisfactory to the Agent;

          (b)  REPRESENTATIONS AND WARRANTIES. The representations and
     warranties of the Borrowers under this Amendment are true and correct in
     all material respects as of such date, as if then made (except to the
     extent that such representations and warranties related solely to an
     earlier date);

          (c)  NO EVENT OF DEFAULT. No Event of Default shall have occurred and
     be continuing nor shall any event have occurred or failed to occur which,
     with the passage of time or service of notice, or both, would constitute an
     Event of Default;

          (d)  OTHER DOCUMENTS. The Agent shall have received such other
     instruments and documents incidental and appropriate to the transaction
     provided for herein as the Agent or its counsel may reasonably request, and
     all such documents shall be in form and substance satisfactory to the
     Agent;

          (e)  LEGAL MATTERS SATISFACTORY. All legal matters incident to the
     consummation of the transactions contemplated hereby shall be reasonably
     satisfactory to special counsel for the Agent retained at the expense of
     Borrowers.

     7.   Borrowers hereby represent and warrant that all factual information
heretofore and contemporaneously furnished by or on behalf of Borrowers to Agent
for purposes of or in connection with this Amendment does not contain any untrue
statement of a material fact or omit

                                       -2-
<Page>

to state any material fact necessary to keep the statements contained herein or
therein from being misleading. Each of the foregoing representations and
warranties shall constitute a representation and warranty of Borrowers made
under the Credit Agreement, and it shall be an Event of Default if any such
representation and warranty shall prove to have been incorrect or false in any
material respect at the time given. Each of the representations and warranties
made under the Credit Agreement (including those made herein) shall survive and
not be waived by the execution and delivery of this Amendment or any
investigation by Lenders.

     8.   The Borrowers agree to indemnify and hold harmless the Lenders and
their respective officers, employees, agents, attorneys and representatives
(singularly, an "Indemnified Party", and collectively, the "Indemnified
Parties") from and against any loss, cost, liability, damage or expense
(including the reasonable fees and out-of-pocket expenses of counsel to the
Lender, including all local counsel hired by such counsel) ("Claim") incurred by
the Lenders in investigating or preparing for, defending against, or providing
evidence, producing documents or taking any other action in respect of any
commenced or threatened litigation, administrative proceeding or investigation
under any federal securities law, federal or state environmental law, or any
other statute of any jurisdiction, or any regulation, or at common law or
otherwise, which is alleged to arise out of or is based upon any acts, practices
or omissions or alleged acts, practices or omissions of the Borrowers or their
agents or arises in connection with the duties, obligations or performance of
the Indemnified Parties in negotiating, preparing, executing, accepting,
keeping, completing, countersigning, issuing, selling, delivering, releasing,
assigning, handling, certifying, processing or receiving or taking any other
action with respect to the Loan Documents and all documents, items and materials
contemplated thereby even if any of the foregoing arises out of an Indemnified
Party's ordinary negligence. The indemnity set forth herein shall be in addition
to any other obligations or liabilities of the Borrowers to the Lenders
hereunder or at common law or otherwise, and shall survive any termination of
this Amendment, the expiration of the Loan and the payment of all indebtedness
of the Borrowers to the Lenders hereunder and under the Notes, provided that the
Borrowers shall have no obligation under this section to the Lenders with
respect to any of the foregoing arising out of the gross negligence or willful
misconduct of the Lenders. If any Claim is asserted against any Indemnified
Party, the Indemnified Party shall endeavor to notify the Borrowers of such
Claim (but failure to do so shall not affect the indemnification herein made
except to the extent of the actual harm caused by such failure). The Indemnified
Party shall have the right to employ, at the Borrowers' expense, counsel of the
Indemnified Parties' choosing and to control the defense of the Claim. The
Borrowers may at their own expense also participate in the defense of any Claim.
Each Indemnified Party may employ separate counsel in connection with any Claim
to the extent such Indemnified Party believes it reasonably prudent to protect
such Indemnified Party. THE PARTIES INTEND FOR THE PROVISIONS OF THIS SECTION TO
APPLY TO AND PROTECT EACH INDEMNIFIED PARTY FROM THE CONSEQUENCES OF STRICT
LIABILITY IMPOSED OR THREATENED TO BE IMPOSED ON ANY INDEMNIFIED PARTY AS WELL
AS FROM THE CONSEQUENCES OF ITS OWN NEGLIGENCE, WHETHER OR NOT THAT NEGLIGENCE
IS THE SOLE, CONTRIBUTING, OR CONCURRING CAUSE OF ANY CLAIM.

     9.   This Amendment may be executed in any number of counterparts and all
of such counterparts taken together shall be deemed to constitute one and the
same instrument.

                                       -3-
<Page>

     10.  WRITTEN CREDIT AGREEMENT. THE CREDIT AGREEMENT, AS AMENDED BY THIS
AMENDMENT REPRESENTS THE FINAL AGREEMENT BETWEEN AND AMONG THE PARTIES AND MAY
NOT BE CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR SUBSEQUENT ORAL
AGREEMENTS OF THE PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN AND
AMONG THE PARTIES.

     11.  NEW LENDERS. Each of Fleet National Bank and Toronto Dominion (Texas),
Inc. hereby agree to become a Lender under the Credit Agreement, to acquire the
Commitment Percentage in the Commitments and the Loans as set forth on the
signature page hereto and to be bound as a Lender by all of the provisions of
the Credit Agreement. The Borrowers and the Agent hereby consent to an
assignment of a portion of the Commitment to Fleet National Bank and Toronto
Dominion (Texas), Inc.

     IN WITNESS WHEREOF, the parties have caused this Amendment to Restated
Credit Agreement to be duly executed as of the date first above written.

                               BORROWERS:

                               EXCO RESOURCES, INC.

                               By: /s/ J. DOUGLAS RAMSEY
                                   ---------------------
                                   J. Douglas Ramsey, Vice President
                                   and Chief Financial Officer

                               EXCO OPERATING, LP
                               a Delaware limited partnership

                               By: EXCO Investment II, LLC,
                                   its General Partner

                                   By:  /s/ T. W. EUBANK
                                        ----------------
                                        T.W. Eubank, President

                                       -4-
<Page>

                               LENDERS:

REVOLVING COMMITMENT           BANK ONE, NA
PERCENTAGE:                    a national banking association
25.0%                          (Main Office Chicago)
                               as a Lender and as Administrative Agent

                               By: /s/ THOMAS K. MARTIN
                                   --------------------
                                   Thomas K. Martin, Associate Director

                                       -5-
<Page>

REVOLVING COMMITMENT           BNP PARIBAS
PERCENTAGE:                    as a Lender and as Syndication Agent
21.4285714%

                               By:    /s/ BETSY JOCHER
                                      ----------------
                               Name:  Betsy Jocher
                               Title: Vice President

                               By:    /s/ POLLY SCHOTT
                                      ----------------
                               Name:  Polly Schott
                               Title: Vice President

                                       -6-
<Page>

REVOLVING COMMITMENT           THE BANK OF NOVA SCOTIA
PERCENTAGE:                    as a Lender and as Documentation Agent
21.4285714%

                               By:    /s/ N. BELL
                                      -----------
                               Name:  N. Bell
                               Title: Assistant Agent

                                       -7-
<Page>

REVOLVING COMMITMENT           COMERICA BANK-TEXAS
PERCENTAGE:
14.2857143%

                               By:    /s/ PETER L. SEFZIK
                                      -------------------
                               Name:  Peter L. Sefzik
                               Title: Assistant Vice President

                                       -8-
<Page>

REVOLVING COMMITMENT           FLEET NATIONAL BANK
PERCENTAGE:
10.7142857%

                               By:    /s/ JEFFREY RATHKAMP
                                      --------------------
                               Name:  Jeffrey Rathkamp
                               Title: Vice President

                                       -9-
<Page>

REVOLVING COMMITMENT           TORONTO DOMINION (TEXAS), INC.
PERCENTAGE:
7.1428571%

                               By:    /s/ ANN S. SLANIS
                                      -----------------
                               Name:  Ann S. Slanis
                               Title: Vice President

                                      -10-
<Page>

                                   SCHEDULE 1

<Table>
<S>                                                                <C>
Bank One, NA                                                       25.000000000%
The Bank of Nova Scotia                                            21.428571429%
BNP Paribas                                                        21.428571429%
Comerica Bank-Texas                                                14.285714286%
Fleet National Bank                                                10.714285714%
Toronto Dominion (Texas), Inc.                                      7.142857143%
</Table>

                                      -11-<Page>

                                                         Exhibits 4.13 And 10.22

                     AMENDMENT TO RESTATED CREDIT AGREEMENT

     THIS AMENDMENT TO RESTATED CREDIT AGREEMENT (hereinafter referred to as the
"Amendment") executed as of the 26th day of April, 2002, by and between ADDISON
ENERGY INC., an Alberta, Canada corporation ("Borrower") and BANK ONE, NA,
CANADA BRANCH ("Bank One"), and each of the financial institutions which is a
party thereto (as evidenced by the signature pages to the Agreement) or which
may from time to time become a party thereto pursuant to the provisions of
Section 28 thereof or any successor or assignee thereof (hereinafter
collectively referred to as "Lenders", and individually, "Lender") and Bank One,
as Administrative Agent (the "Agent"), BNP Paribas (Canada), as Syndication
Agent, The Bank of Nova Scotia, as Documentation Agent and Banc One Capital
Markets, Inc., as Lead Arranger and Bookrunner ("Arranger").

                                   WITNESSETH:

     WHEREAS, as of April 26, 2001, Borrower, the Lenders and the Agent entered
into a Credit Agreement pursuant to which the Lenders made available to the
Borrowers certain credit facilities in the form therein described; and

     WHEREAS, as of December 18, 2001, Borrower, Lenders and Agent entered into
a Restated Credit Agreement (the "Credit Agreement"); and

     WHEREAS, the Borrower has requested that the Lenders agree to make certain
additional amendments to the Credit Agreement and the Lenders, together with
certain additional financial institutions who shall become a party to the Credit
Agreement at the Amendment Effective Date (as hereinafter defined), have agreed
to do so on the terms and conditions hereinafter set forth.

     NOW, THEREFORE, the parties agree to amend the Credit Agreement as follows:

     1.   Unless otherwise defined herein all defined terms used herein shall
have the same meaning as ascribed to such terms in the Credit Agreement.

     2.   The Lenders have agreed to increase their Commitments to Borrower and
in connection therewith reallocate their respective Commitments and allow Fleet
National Bank and The Toronto-Dominion Bank to acquire an interest in the
Commitments and the Loans. After such increase and reallocation of the
Commitments, the Lenders shall own the Revolving Commitment Percentages set
forth on the signature pages hereto at the Amendment Effective Date. Each Lender
shall surrender its existing Note and be issued a new Note in a face amount
equal to each Lender's Revolving Commitment Percentage times $250,000,000
Canadian. Each said Note to be in the form of Exhibit "B" to the Credit
Agreement with appropriate insertions.

<Page>

     3.   As of the Amendment Effective Date, the Borrowing Base shall be U.S.
$75,000,000 or the Canadian dollar equivalent until redetermined pursuant to the
provisions of Section 7(b) of the Credit Agreement.

     4.   Except to the extent its provisions are specifically amended, modified
or superseded by this Amendment, the representations, warranties and affirmative
and negative covenants of the Borrower contained in the Credit Agreement are
incorporated herein by reference for all purposes as if copied herein in full.
The Borrower hereby restates and reaffirms each and every term and provision of
the Credit Agreement, as amended, including, without limitation, all
representations, warranties and affirmative and negative covenants. Except to
the extent its provisions are specifically amended, modified or superseded by
this Amendment, the Credit Agreement, as amended, and all terms and provisions
thereof shall remain in full force and effect, and the same in all respects are
confirmed and approved by the Borrower and the Lenders.

     5.   This Amendment shall be effective as of the date first above written,
but only upon the satisfaction of the conditions precedent set forth in
Paragraph 6 hereof.

     6.   The obligations of Lenders under this Amendment shall be subject to
the following conditions precedent:

          (a)  EXECUTION AND DELIVERY. The Borrower shall have executed and
     delivered this Amendment, and other required documents, all in form and
     substance satisfactory to the Agent;

          (b)  REPRESENTATIONS AND WARRANTIES. The representations and
     warranties of the Borrower under this Amendment are true and correct in all
     material respects as of such date, as if then made (except to the extent
     that such representations and warranties related solely to an earlier
     date);

          (c)  NO EVENT OF DEFAULT. No Event of Default shall have occurred and
     be continuing nor shall any event have occurred or failed to occur which,
     with the passage of time or service of notice, or both, would constitute an
     Event of Default;

          (d)  OTHER DOCUMENTS. The Agent shall have received such other
     instruments and documents incidental and appropriate to the transaction
     provided for herein as the Agent or its counsel may reasonably request, and
     all such documents shall be in form and substance satisfactory to the
     Agent;

          (e)  LEGAL MATTERS SATISFACTORY. All legal matters incident to the
     consummation of the transactions contemplated hereby shall be reasonably
     satisfactory to special counsel for the Agent retained at the expense of
     Borrower.

     7.   Borrower hereby represents and warrants that all factual information
heretofore and contemporaneously furnished by or on behalf of Borrower to Agent
for purposes of or in connection with this Amendment does not contain any untrue
statement of a material fact or omit

                                       -2-
<Page>

to state any material fact necessary to keep the statements contained herein or
therein from being misleading. Each of the foregoing representations and
warranties shall constitute a representation and warranty of Borrower made under
the Credit Agreement, and it shall be an Event of Default if any such
representation and warranty shall prove to have been incorrect or false in any
material respect at the time given. Each of the representations and warranties
made under the Credit Agreement (including those made herein) shall survive and
not be waived by the execution and delivery of this Amendment or any
investigation by Lenders.

     8.   The Borrower agrees to indemnify and hold harmless the Lenders and
their respective officers, employees, agents, attorneys and representatives
(singularly, an "Indemnified Party", and collectively, the "Indemnified
Parties") from and against any loss, cost, liability, damage or expense
(including the reasonable fees and out-of-pocket expenses of counsel to the
Lender, including all local counsel hired by such counsel) ("Claim") incurred by
the Lenders in investigating or preparing for, defending against, or providing
evidence, producing documents or taking any other action in respect of any
commenced or threatened litigation, administrative proceeding or investigation
under any federal securities law, federal or state environmental law, or any
other statute of any jurisdiction, or any regulation, or at common law or
otherwise, which is alleged to arise out of or is based upon any acts, practices
or omissions or alleged acts, practices or omissions of the Borrower or its
agents or arises in connection with the duties, obligations or performance of
the Indemnified Parties in negotiating, preparing, executing, accepting,
keeping, completing, countersigning, issuing, selling, delivering, releasing,
assigning, handling, certifying, processing or receiving or taking any other
action with respect to the Loan Documents and all documents, items and materials
contemplated thereby even if any of the foregoing arises out of an Indemnified
Party's ordinary negligence. The indemnity set forth herein shall be in addition
to any other obligations or liabilities of the Borrower to the Lenders hereunder
or at common law or otherwise, and shall survive any termination of this
Amendment, the expiration of the Loan and the payment of all indebtedness of the
Borrower to the Lenders hereunder and under the Notes, provided that the
Borrower shall have no obligation under this section to the Lenders with respect
to any of the foregoing arising out of the gross negligence or willful
misconduct of the Lenders. If any Claim is asserted against any Indemnified
Party, the Indemnified Party shall endeavor to notify the Borrower of such Claim
(but failure to do so shall not affect the indemnification herein made except to
the extent of the actual harm caused by such failure). The Indemnified Party
shall have the right to employ, at the Borrower's expense, counsel of the
Indemnified Parties' choosing and to control the defense of the Claim. The
Borrowers may at their own expense also participate in the defense of any Claim.
Each Indemnified Party may employ separate counsel in connection with any Claim
to the extent such Indemnified Party believes it reasonably prudent to protect
such Indemnified Party. THE PARTIES INTEND FOR THE PROVISIONS OF THIS SECTION TO
APPLY TO AND PROTECT EACH INDEMNIFIED PARTY FROM THE CONSEQUENCES OF STRICT
LIABILITY IMPOSED OR THREATENED TO BE IMPOSED ON ANY INDEMNIFIED PARTY AS WELL
AS FROM THE CONSEQUENCES OF ITS OWN NEGLIGENCE, WHETHER OR NOT THAT NEGLIGENCE
IS THE SOLE, CONTRIBUTING, OR CONCURRING CAUSE OF ANY CLAIM.

     9.   This Amendment may be executed in any number of counterparts and all
of such counterparts taken together shall be deemed to constitute one and the
same instrument.

                                       -3-
<Page>

     10.  WRITTEN CREDIT AGREEMENT. THE CREDIT AGREEMENT, AS AMENDED BY THIS
AMENDMENT REPRESENTS THE FINAL AGREEMENT BETWEEN AND AMONG THE PARTIES AND MAY
NOT BE CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR SUBSEQUENT ORAL
AGREEMENTS OF THE PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN AND
AMONG THE PARTIES.

     11.  NEW LENDERS. Each of Fleet National Bank and The Toronto-Dominion Bank
hereby agree to become a Lender under the Credit Agreement, to acquire the
Commitment Percentage in the Commitments and the Loans as set forth on the
signature page hereto and to be bound as a Lender by all of the provisions of
the Credit Agreement. The Borrower and the Agent hereby consent to an assignment
of a portion of the Commitment to Fleet National Bank and The Toronto-Dominion
Bank.

     IN WITNESS WHEREOF, the parties have caused this Amendment to Restated
Credit Agreement to be duly executed as of the date first above written.

                               BORROWER:

                               ADDISON ENERGY INC.

                               By:   /s/ J. DOUGLAS RAMSEY
                                     ---------------------
                                     J. Douglas Ramsey, Vice President
                                     and Chief Financial Officer

                                       -4-
<Page>

                               LENDERS:

REVOLVING COMMITMENT           BANK ONE, NA CANADA BRANCH
PERCENTAGE:                    as a Lender and as Administrative Agent
25.0%

                               By:    /s/ MICHAEL TAM
                                      ---------------
                               Name:  Michael Tam
                               Title: Director

                                       -5-
<Page>

REVOLVING COMMITMENT           BNP PARIBAS (CANADA)
PERCENTAGE:                    as a Lender and as Syndication Agent
21.4285714%

                               By:    /s/ MICHAEL GOSSELLN
                                      --------------------
                               Name:  Michael Gosselln
                               Title: Director, Energy & Project Finance

                               By:    /s/ JEAN-PHILIPPE CADOT
                                      -----------------------
                               Name:  Jean-Philippe Cadot
                               Title: Vice President, Corporate Banking

                                       -6-
<Page>

REVOLVING COMMITMENT           THE BANK OF NOVA SCOTIA
PERCENTAGE:                    as a Lender and as Documentation Agent
21.4285714%

                               By:    /s/ BRIAN WILLIAMSON
                                      --------------------
                               Name:  Brian Williamson
                               Title: Director

                                       -7-
<Page>

REVOLVING COMMITMENT           COMERICA BANK, CANADA BRANCH
PERCENTAGE:
14.2857143%

                               By:    /s/ ROBERT ROSEN
                                      ----------------
                               Name:  Robert Rosen
                               Title: Vice-President

                                       -8-
<Page>

REVOLVING COMMITMENT           FLEET NATIONAL BANK
PERCENTAGE:
10.7142857%

                               By:    /s/ JEFFREY RATHKAMP
                                      --------------------
                               Name:  Jeffrey Rathkamp
                               Title: Vice President

                                       -9-
<Page>

REVOLVING COMMITMENT           THE TORONTO-DOMINION BANK
PERCENTAGE:
7.1428571%

                               By:    /s/ DEBBI L. BRITO
                                      ------------------
                               Name:  Debbi L. Brito
                               Title: Asst. Mngr.
                                      Credit Compliance & Administration

                                      -10-
<Page>

                                   SCHEDULE 1

<Table>
<S>                                                                <C>
Bank One, NA, Canada Branch                                        25.000000000%
The Bank of Nova Scotia                                            21.428571429%
BNP Paribas (Canada)                                               21.428571429%
Comerica Bank, Canada Branch                                       14.285714286%
Fleet National Bank                                                10.714285714%
The Toronto-Dominion Bank                                           7.142857143%
</Table>

                                      -11-

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