Document:

<PAGE>   1
                                                                  EXHIBIT  10.19

                    FIRST AMENDMENT TO EXPLORATION AGREEMENT

         This First Amendment to Exploration Agreement ("Amendment") is made
and entered into this the third day of November 1999, between THE HOUSTON
EXPLORATION COMPANY, a Delaware corporation, of 1100 Louisiana Street, Suite
2000, Houston, Texas 77002 ("THEC") and KEYSPAN EXPLORATION AND PRODUCTION,
L.L.C., a Delaware limited liability company, of One Metro Tech Centre, 18th
Floor, Brooklyn, New York 11201 ("KE&P").

                              W I T N E S S E T H:

         A.       THEC and KE&P have entered into that certain Exploration
Agreement dated the 15th day of March 1999 between The Houston Exploration
Company and KeySpan Exploration and Production, L.L.C. ("Exploration
Agreement"); and

         B.       THEC and KE&P desire to amend the Exploration Agreement as
set forth in this Amendment.

         NOW, THEREFORE, for valuable consideration, THEC and KE&P agree as
follows:

                                       I.

          Section 1.15 of the Exploration Agreement is amended so that the
existing language becomes Section 1.15(a) and the following is inserted as
Section 1.15(b):

         1.15(b) KE&P's Quarterly Commitment. The sum of (a) 25 million dollars
per calendar quarter during the Primary Term plus (b) that portion of prior
quarters' Quarterly Commitments that have not been expended or committed for
expenditure under this Agreement which sum shall be used to pay all costs
attributable to to KE&P under this Agreement, including G and A Costs, during
the relevant quarter.

<PAGE>   2
                                      II.

         Section 1.28 of the Agreement is deleted and the following new Section
1.28 is substituted therefor:

         1.28 Program Year. Each calendar year (or portion of a calendar year
if the Primary Term ends at the end of any calendar quarter during such year
other than December 31 of such year) during the Primary Term of this Agreement.
A cost under this Agreement for purposes of Payout shall be attributable to the
Program Year in which the first Exploratory Well is spudded on the Lease to
which such cost relates. If an Exploratory Well is not spudded on a Lease
during the Primary Term of this Agreement, the costs relating to such Lease
shall be used in the calculation of Payout for the Program Year in which they
were incurred. Net Proceeds shall be attributable to the Program Year in which
the first Exploratory Well is spudded on the Lease to which such proceeds
relate.

                                      III.

         Section 2.1 of the Agreement is deleted and the following new Section
2.1 is substituted therefor:

         2.1      Primary Term.  This Agreement shall be for a primary term
(the "Primary Term") commencing on January 1, 1999 ("Commencement Date") and
ending on the earliest to occur of the following:

                  (a)      December 31, 2001;

                  (b) the end of any calendar quarter if either party notifies
the other party in writing on or before thirty (30) days before the end of such
quarter of its election to terminate the Primary Term at the end of such
quarter; or
                  (c)      the mutual agreement of the parties.

                                       2

<PAGE>   3

                                      IV.

         Section 5.1 of the Agreement is deleted and the following new Section
5.1 is substituted therefor:

         5.1 Allocation of IDCs. Subject to Section 5.4, during each year of
the Primary Term, KE&P shall pay one hundred percent (100%) of all Intangible
Costs attributable to THEC's Original Working Interests in the Leases until
KE&P has paid Intangible Costs for such year totaling 20.725 million dollars
and, thereafter during such year KE&P shall pay fifty one and seventy five one
hundredths percent (51.75%) of all Intangible Costs attributable to THEC's
Original Working Interests in the Leases and THEC shall pay forty eight and
twenty five one hundredths percent (48.25%) of all Intangible Costs
attributable to THEC's Original Working Interest in the Leases. If during any
of such years, one hundred percent (100%) of the Intangible Costs attributable
to THEC's Original Working Interests in the Leases are less than 20.725 million
dollars, the shortage shall be added to the following year and KE&P shall pay
during such following year one hundred percent (100%) of all Intangible Costs
attributable to THEC's Original Working Interests in the Leases until KE&P has
paid Intangible Costs for such year totaling 20.725 million dollars plus the
shortage from the preceding year(s); provided that, during the first calendar
quarter of the 2000 Program Year, KE&P's obligation to pay one hundred percent
(100%) of such Intangible Costs shall be limited to 5.18 million dollars and,
further provided, if the Primary Term ends on March 31, 2000 KE&P's obligation
to pay one hundred percent (100%) of Intangible Costs shall terminate. Subject
to the preceding sentence, during the Secondary Term, KE&P shall pay all
Intangible Costs attributable to THEC's Original Working Interest in the Leases
until such shortage from the Primary Term, if any, is

                                       3

<PAGE>   4

expended and thereafter shall pay fifty one and seventy five one hundredths
percent (51.75%) of all Intangible Costs attributable to THEC's Original
Working Interest in the Leases and THEC shall pay forty eight and twenty five
one hundredths percent (48.25%) of all Intangible Costs attributable to THEC's
Original Working Interest in the Leases; provided that, KE&P shall have no
obligation to pay Intangible Costs to the extent such costs relate to a Lease
reassigned to THEC under Section 6.5 and such costs accrue after such
reassignment.

                                       V.

         Section 5.3 of the Agreement is deleted and the following new Section
5.3 is substituted therefor:

         5.3 Allocation of Remaining Costs. Subject to Section 5.4 and 5.8,
during the Primary Term and the Secondary Term, KE&P shall pay forty five
percent (45%) of all Drilling Costs, Development Costs, Seismic Costs,
Leasehold Costs, Abandonment Costs and Operating Costs attributable to THEC's
Original Working Interest in the Leases and THEC shall pay fifty five percent
(55%) of all Drilling Costs, Development Costs, Seismic Costs, Leasehold Costs,
Abandonment Costs and Operating Costs attributable to THEC's Original Working
Interest in the Leases; provided that, KE&P shall have no obligation to pay
any of such costs to the extent such costs relate to a Lease reassigned to THEC
under Section 6.5 and such costs accrue after such reassignment.

                                      VI.

         Section 5.4 of the Agreement is amended so that the existing language
becomes Section 5.4A and the following is inserted as 5.4B:

                                       4

<PAGE>   5

         5.4B Primary Term Commitment. Notwithstanding the foregoing Section
5.4A, for the period commencing January 1, 2000, this Section 5.4B shall apply
prospectively in lieu of Section 5.4A. KE&P's obligation to pay the costs
specified in Sections 5.1 to 5.3 incurred during any quarter of the Primary
Term is limited to KE&P's Quarterly Commitment subject to the following:

         (a) If THEC determines that the allocation to KE&P of its share of the
Drilling Costs and Intangible Costs of the first Exploratory Well on a Lease
will result in KE&P's Quarterly Commitment being exceeded, THEC shall notify
KE&P in writing of such fact prior to commencing such Well. Within fifteen (15)
days (or such lesser period specified in the notice if the proposed spud date
of such Well is less than thirty (30) days from the date of such notice) after
receiving such notice, KE&P shall notify THEC in writing whether or not it
approves such Well. If KE&P approves such Well, KE&P's share of the Drilling
Costs and Intangible Costs of such Well shall be deemed "Excess
Costs" and, to the extent the Excess Costs result in KE&P's Quarterly
Commitment being exceeded, such commitment shall be increased accordingly for
such quarter. If KE&P does not approve such Well or fails to notify THEC of its
decision, KE&P shall forfeit its interests in such Well and the Lease on which
it is located.

         (b) Except as provided in Section 5.4(a), if KE&P is not obligated to
pay a portion of its share of the costs specified in Sections 5.1 to 5.3 during
any quarter of the Primary Term, because its share exceeds in whole or in part
KE&P's Quarterly Commitment, and THEC pays such costs, KE&P shall reimburse
THEC for such costs out of KE&P's Quarterly Commitment for the following
quarter on or before thirty days after the end of the

                                       5

<PAGE>   6

quarter in which THEC paid such costs or, if the Primary Term has ended, THEC
shall receive KE&P's share of Net Proceeds from all Wells drilled under this
Agreement until such time as THEC has received a sum of money (exclusive of all
Burdens, Marketing Costs and Taxes) out of such share equal to KE&P's share of
costs which were paid by THEC, provided, however, that the amount to be paid by
KE&P as contemplated above shall not exceed twenty percent (20%) of KE&P's
Quarterly Commitment without its written consent.

         (c) KE&P's Quarterly Commitment shall first be applied to G and A
Costs, Seismic Costs, Leasehold Costs and Operating Costs and the remainder to
the Intangible Costs, Drilling Costs, Development Costs and Abandonment Costs.

         (d) All Drilling Costs, Intangible Costs and Development Costs for
purposes of applying the limitations of KE&P's Quarterly Commitment shall, at
the election of THEC, be deemed to have been incurred entirely on the date THEC
submits to KE&P the information set forth in Section 7.3 relating to the
applicable operation or the date of the AFE relating to the expenditure of such
costs, rather than on the dates such costs are actually incurred.

         (e) Such portion of KE&P's Yearly Commitment for the year 1999 not
expended or committed for expenditure by December 31, 1999 shall be available
for use during the Primary Term only for Development Costs and Intangible Costs
related to Development Operations on Leases on which the first Exploratory Well
was spudded during the 1999 Program Year.

         (f) Such portion of KE&P's Quarterly Commitment, for any calendar
quarter, not

                                       6

<PAGE>   7

expended or committed for expenditure by the last day of such quarter shall be
available for use in subsequent quarters during the Primary Term only for
Development Costs and Intangible Costs related to Development Operations on
Leases on which the first Exploratory Well was spudded during the quarter to
which the unused portion of the quarterly Commitment relates, or any previous
quarter, including the 1999 Program Year.

                                      VII.

         Section 10.4 of the Exploration Agreement is amended so that the
existing language becomes Section 10.4(a) and the following is inserted as
Section 10.4(b):

         10.4(b) Budgets. Notwithstanding the foregoing Section 10.4(a), for
the period commencing January 1, 2000, this Section 10.4(b) shall apply
prospectively in lieu of Section 10.4(a). THEC shall submit quarterly to the
Management Committee THEC's Program Budget and a quarterly budget setting forth
the anticipated financial
requirements of KE&P under this Agreement. Such budgets for the first quarter
of the year 2000 shall be submitted on or before January 1, 2000 and the
budgets for the following quarters during the terms on or before the first day
of such quarters.

         Except as herein amended, the parties do hereby ratify and confirm the
Exploration Agreement.

         Executed on the day set forth above, but to be effective as of
January 1, 2000.

                                       THE HOUSTON EXPLORATION COMPANY

                                       By:  /s/ James Westmoreland
                                           ----------------------------------
                                           James Westmoreland, Vice President

                                       KEYSPAN EXPLORATION AND
                                         PRODUCTION, L.L.C.

                                       By: /s/ Zain Mirza
                                           -----------------------------------
                                           Zain Mirza, Vice President

                                       7<PAGE>   1
                                                                  EXHIBIT 10.23

                         THIRD AMENDMENT TO AMENDED AND
                           RESTATED CREDIT AGREEMENT

         This THIRD AMENDMENT AND SUPPLEMENT TO AMENDED AND RESTATED CREDIT
AGREEMENT (this "Third Amendment") executed effective as of December 9, 1999
(the "Effective Date"), is by and among THE HOUSTON EXPLORATION COMPANY, a
Delaware corporation ("Company"); CHASE BANK OF TEXAS, NATIONAL ASSOCIATION (in
its individual capacity, "Chase"), as agent (in such capacity, "Agent") for
each of the lenders that is a signatory hereto or which becomes a signatory
hereto and to the hereinafter described Credit Agreement as provided in Section
12.06 of the Credit Agreement (individually, together with its successors and
assigns, "Lender" and collectively, "Lenders").

                                R E C I T A L S

         A. The Company, the Agent and the Lenders (other than the hereinafter
defined "Additional Lenders") are parties to that certain Amended and Restated
Credit Agreement dated as of March 30, 1999 (said Amended and Restated Credit
Agreement, as amended and supplemented by First Amendment to Amended and
Restated Credit Agreement dated as of May 4, 1999, and as further amended by
Second Amendment to Amended and Restated Credit Agreement dated as of October
6, 1999, "Credit Agreement"), pursuant to which the Lenders agreed to make
loans and issue Letters of Credit to and for the account of the Company.

         B.       The Company, the Lenders and the Agent mutually desire to
amend certain aspects of the Credit Agreement relating to, among other things,
the Borrowing Base and Threshold Amount.

         C.       In view of the foregoing, the Company, the Agent and the
Lenders hereby agree to amend the Credit Agreement in the particulars
hereinafter provided.

         NOW, THEREFORE, in consideration of the premises and other good and
valuable consideration and the mutual benefits, covenants and agreements herein
expressed, the parties hereto now agree as follows:

         Section 1. Certain Terms. All capitalized terms used in this Third
Amendment and not otherwise defined herein shall have the meanings ascribed to
such terms in the Credit Agreement.

         Section 2.  Amendments and Supplements to Credit Agreement.  The
Credit Agreement is hereby amended and supplemented as follows:

                  2.1  Definitions.

                  (a) The following terms defined in Section 1.02 of the Credit
         Agreement are hereby amended as follows:

<PAGE>   2
                           (i)  The term "Agreement" is hereby amended in its
                  entirety to read as follows:

                           "Agreement" shall mean this Credit Agreement, as
                  amended by the First Amendment, as further amended by the
                  Second Amendment, as further amended by the Third Amendment,
                  and as the same may be further amended or supplemented from
                  time to time.

                           (ii) The term "Applicable Margin" is hereby amended
                  in its entirety to read as follows:

         "Applicable Margin" shall mean at the time of calculation, with
respect to any Loan, calculated as a function of the type of such Loan, the
following rate per annum as applicable:

<TABLE>
<CAPTION>
--------------------------------------------------------------------------------------------
   THRESHOLD AMOUNT                FIXED RATE LOAN APPLICABLE      BASE RATE LOAN APPLICABLE
     UTILIZATION                       MARGIN PERCENTAGE              MARGIN PERCENTAGE
--------------------------------------------------------------------------------------------
<S>                                <C>                             <C>
Less than 33%                               0.875%                           0%
Greater than or equal to 33%                1.125%                           0%
but less than 66%
Greater than or equal to 66%                1.375%                           0%
but less than 100%
Greater than or equal to                    1.625%                           0%
100%
--------------------------------------------------------------------------------------------
</TABLE>

                           (iii) The Term "Threshold Amount" is hereby amended
                  in its entirety to read as follows:

                                    "Threshold Amount" shall mean (i) during
                           the period from and including the Effective Date of
                           the Third Amendment to and including the date of the
                           redetermination by the Agent and the Lenders of the
                           Threshold Amount scheduled to occur March 1, 2000,
                           an amount equal to $175,000,000, (ii) during the
                           period from and including March 2, 2000 to and
                           including September 1, 2000, an amount equal to the
                           amount of the March 1, 2000 redetermined Threshold
                           Amount, and (iii) thereafter, the amount equal to
                           the Borrowing Base in effect from time to time. The
                           redetermination of the Threshold Amount on March 1,
                           2000, shall be made using the same criteria used by
                           the Agent and the Lenders prior to the Closing Date
                           to determine the Threshold Amount.

                  (b) Section 1.02 of the Credit Agreement is hereby
         supplemented, where alphabetically appropriate, with the addition of
         the following definition:

                                      -2-

<PAGE>   3
                           "Third Amendment" shall mean that certain Third
                  Amendment to Amended and Restated Credit Agreement dated
                  effective as of December 9, 1999, between the Company, the
                  Agent and the Lenders.

                  2.2  Fees.  Section 2.04 of the Credit Agreement is hereby
          amended as follows:

         (a)      The table found in Section 2.04(a)(i) is hereby amended in
its entirety to read as follows:

------------------------------------------------------------------------------
          THRESHOLD AMOUNT
            UTILIZATION                                 COMMITMENT FEE
------------------------------------------------------------------------------
Less than 33%                                               0.25%
Greater than or equal to 33% but less than 66%              0.30%
Greater than or equal to 66% but less than 100%             0.30%
Greater than or equal to 100%                               0.375%

         (b)      The table found in Section 2.04(b) is hereby amended in its
entirety to read as follows:

------------------------------------------------------------------------------
                 THRESHOLD AMOUNT
                    UTILIZATION                         ISSUANCE FEE
------------------------------------------------------------------------------
Less than 33%                                              0.875%
Greater than or equal to 33% but less                      1.125%
than 66%
Greater than or equal to 66% but less                      1.375%
than 100%
Greater than or equal to 100%                              1.625%
------------------------------------------------------------------------------

                  2.3 Prepayments. Section 2.08(b) of the Credit Agreement is
         hereby amended and modified to provide that, if on March 29, 2000, the
         sum of the outstanding aggregate principal amount of the Loans and the
         LC Exposure exceeds the lesser of the then effective Borrowing Base or
         the aggregate amount of the Commitments, then the Company shall
         immediately pay or prepay the amount of such excess amount for
         application first, towards the reduction of all amounts previously
         drawn under Letters of Credit, but not yet funded as a Revolving
         Credit Loan pursuant to Section 4.07(b) or reimbursed, second, if
         necessary, towards reduction of the outstanding principal balance of
         the Notes by prepaying Base Rate Loans, if any, then outstanding, and
         third, if necessary, at the election of the Company, either toward a
         reduction of the outstanding principal balance of the Notes by
         prepaying Fixed Rate Loans, if any, then outstanding or by paying such
         amount to the Agent as cash collateral for outstanding Letters of
         Credit, which amount shall be held by the Agent as cash collateral to

                                      -3-

<PAGE>   4
         secure the Company's obligation to reimburse the Agent and the Lenders
         for drawing under the Letters of Credit.

                  2.4  MarketSpan Credit Facility.  Section 8.07 of the Credit
         Agreement is hereby amended in its entirety to read as follows:

                           "Section 8.07 MarketSpan Credit Facility. The
                  Company shall maintain an unused and available commitment
                  under the MarketSpan Credit Facility equal to or greater than
                  the amount by which the Borrowing Base exceeds the Threshold
                  Amount until (i) such time as the Borrowing Base is equal to
                  the Threshold Amount, (ii) such time as any and all
                  prepayments required under Section 2.08(b) have been made in
                  full, and (iii) such time as no Default exists hereunder."

         Section 3.  Borrowing Base; Threshold Amount.  Notwithstanding anything
         to the contrary contained in the Credit Agreement including, without
         limitation, the provisions of Section 2.09:

                  (a) The amount of the Borrowing Base shall be (i)
         $240,000,000 for the period from and including the Effective Date of
         this Third Amendment to but not including March 29, 2000, and (ii) an
         amount equal to the Threshold Amount in effect on March 29, 2000, for
         the period from and including March 29, 2000 to and including
         September 1, 2000, at which time and from time to time thereafter the
         Borrowing Base shall be redetermined in accordance with Section 2.09
         of the Credit Agreement.

                  (b) Any unscheduled redetermination of the Borrowing Base or
         the Threshold Amount which occurs on or before March 29, 2000, must be
         approved by all of the Lenders.

         Section 4. Conditions. In addition to any and all other applicable
conditions precedent contained in Article VI of the Credit Agreement, this
Third Amendment shall become binding upon receipt by the Agent of the following
documents, each of which shall be satisfactory to the Agent in form and
substance:

                  (a)  Counterparts of this Third Amendment duly executed by
         the Company.

                  (b)  Photocopies of all duly completed and executed
         documentation evidencing the extension of the final maturity of the
         MarketSpan Credit Facility from January 1, 2000 to March 31, 2000.

                  (c)  Such other documents as the Agent or its counsel may
         reasonably request.

         Section 5. Extent of Amendments. The parties hereto hereby acknowledge
and agree that, except as specifically supplemented and amended, changed or
modified hereby, the Credit Agreement shall remain in full force and effect in
accordance with its terms.

                                      -4-

<PAGE>   5
         Section 6. Reaffirmation. The Company hereby reaffirms that as of the
date of this Third Amendment, the representations and warranties made by the
Company in Article VII of the Credit Agreement are true and correct on the date
hereof as though made on and as of the date of this Third Amendment.

         Section 7.  Governing Law.  This Third Amendment shall be governed by,
and construed in accordance with, the laws of the State of Texas.

         Section 8. Counterparts. This Third Amendment may be executed in two
or more counter parts, and it shall not be necessary that the signatures of all
parties hereto be contained on any one counterpart hereof; each counterpart
shall be deemed an original, but all of which together shall constitute one and
the same instrument.

         Section 9. Final Agreement. THE CREDIT AGREEMENT, AS AMENDED HEREBY,
THIS THIRD AMENDMENT, THE NOTES AND THE SECURITY INSTRUMENTS REPRESENT THE
FINAL AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF
PRIOR, CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES. THERE ARE
NO UNWRITTEN OR ORAL AGREEMENTS BETWEEN THE PARTIES.

                      [SIGNATURE PAGES BEGIN ON NEXT PAGE]

                                      -5-

<PAGE>   6
         IN WITNESS WHEREOF, the parties hereto have caused this Third
Amendment to be duly executed effective as of the date first above written.

                                       COMPANY:

                                       THE HOUSTON EXPLORATION COMPANY

                                       By:   /s/ Thomas W. Powers
                                          --------------------------------
                                       Name:     Thomas W. Powers
                                       Title:    Senior Vice President
                                                 Business Development
                                                 Finance and Treasurer

                                       Address:   1100 Louisiana
                                                  Suite 2000
                                                  Houston, Texas  77002

                                       Telecopier No.:  713/830-6885

                                       Telephone No.:  713/830-6853

                        [Third Amendment to Amended and
                           Restated Credit Agreement
                               Signature Page 1]

<PAGE>   7
                                          LENDERS AND AGENTS:
                                          ------------------

                                          CHASE BANK OF TEXAS, NATIONAL
                                          ASSOCIATION, individually as a
                                            Lender and as Administrative Agent

                                          By: /s/ Russell Johnson
                                             -------------------------------
                                          Name:   Russell Johnson
                                          Title:  Vice President

                                          Applicable Lending Office for Base
                                            Rate Loans:

                                          Address:  712 Main Street
                                                    Houston, Texas  77002

                                          Applicable Lending Office for Fixed
                                            Rate Loans:

                                          Address:    712 Main Street
                                                      Houston, Texas  77002
                                          Telecopier: 713/216-8870
                                          Telephone:  713/216-5617

                                          Address for Notices:

                                          Loan and Agency Services
                                          The Chase Manhattan Bank
                                          1 Chase Manhattan Plaza, 8th Floor
                                          New York, New York  10081

                                          Telecopier No.:  212/552-7490
                                          Telephone No.:   212/552-7943

                                          Attention: Muniram Appanna

                        [Third Amendment to Amended and
                           Restated Credit Agreement
                               Signature Page 2]

<PAGE>   8
                           HE BANK OF NOVA SCOTIA,
                           individually as a Lender and as Syndication
                           Agent

                           By:    /s/F.C.H. Ashby
                              ----------------------------------
                           Name:  F.C.H. Ashby
                           Title: Senior Manager Loan Operations

                           Applicable Lending Office for Base Rate Loans:

                           Address:  600 Peachtree Street N.E.
                                     Suite 2700
                                     Atlanta GA 30308

                           Applicable Lending Office for Fixed Rate Loans:

                           Address:  600 Peachtree Street N.E.
                                     Suite 2700
                                     Atlanta GA 30308

                           Address for Notices:

                                     1100 Louisiana, Suite 3000
                                     Houston, Texas 77002

                                     Telecopier No.:  713/752-2425
                                     Telephone No.:  713/759-3441

                                     Attention: Mark Ammerman

                                     with a copy to:

                                     Address:  600 Peachtree Street N.E.
                                                      Suite 2700
                                                      Atlanta GA 30308
                                    Telecopier:       404/888-8998
                                    Telephone:        404/877-1552
                                    Attention:        Phyllis Walker

                        [Third Amendment to Amended and
                           Restated Credit Agreement
                               Signature Page 3]

<PAGE>   9
                                  FIRST UNION NATIONAL BANK,
                                  Individually as a Lender and as
                                  Documentation Agent

                                  By: /s/ Robert R. Wetteroff
                                     ----------------------------------
                                  Name: Robert R. Wetteroff
                                  Title: Senior Vice President

                                  Applicable Lending Office for Base Rate Loans:

                                  Address:   301 South College Street
                                             Charlotte, North Carolina 28288

                                  Applicable Lending Office for Fixed Rate
                                             Loans:

                                  Address:   301 South College Street
                                             Charlotte, North Carolina 28288

                                  Address for Notices:

                                  1001 Fannin Street
                                  Houston, Texas 77002

                                  Telecopier:    713/650-6354
                                  Telephone No.  713/346-2727

                                  Attention:  Jay Chernosky

                                  with a copy to:

                                  1001 Fannin Street
                                  Houston, Texas 77002

                                  Telecopier:    713/650-6354
                                  Telephone No.  713/346-2727

                                  Attention:  Debbie Blank

                        [Third Amendment to Amended and
                           Restated Credit Agreement
                               Signature Page 4]

<PAGE>   10
                                 PNC BANK NATIONAL ASSOCIATION,
                                 Individually as a Lender and as Managing
                                 Agent

                                 By: /s/ Thomas A. Maleski
                                    --------------------------------
                                 Name: Thomas a. Maleski
                                 Title: Vice President

                                 Applicable Lending Office for Base Rate Loans:

                                 Address:  249 Fifth Avenue, 3rd Floor
                                           Mail Stop P1-POPP-03-1
                                           Pittsburgh, Pennsylvania 15222

                                 Applicable Lending Office for Fixed Rate
                                            Loans:

                                 Address:  249 Fifth Avenue, 3rd Floor
                                           Mail Stop P1-POPP-03-1
                                           Pittsburgh, Pennsylvania 15222

                                 Address for Notices:

                                 249 Fifth Avenue, 3rd Floor
                                 Mail Stop P1-POPP-03-1
                                 Pittsburgh, Pennsylvania 15222

                                 Telecopier:   412/762-2571
                                 Telephone No. 412/762-3025

                                 Attention:  Thomas A. Majeski

                                 with a copy to:

                                 620 Liberty Avenue
                                 Mail Stop P2-PTPP-03-1
                                 Pittsburgh, Pennsylvania 15222

                                 Telecopier:   412/762-5271
                                 Telephone No. 412/762-3025

                                 Attention:  Stephanie Angelini

                        [Third Amendment to Amended and
                           Restated Credit Agreement
                               Signature Page 5]

<PAGE>   11
                                 COMERICA BANK - TEXAS

                                 By: /s/ Martin W. Wilson
                                    ---------------------------------
                                 Name: Martin W. Wilson
                                 Title: Vice President

                                 Applicable Lending Office for Base Rate Loans:

                                 Address:  1601 Elm Street, 2nd Floor
                                           Dallas, Texas 75201

                                 Applicable Lending Office for Fixed Rate
                                            Loans:

                                 Address:  1601 Elm Street, 2nd Floor
                                           Dallas, Texas 75201

                                 Address for Notices:

                                 1601 Elm Street, 2nd Floor
                                 Dallas, Texas 75201

                                 Telecopier:     214/969-6561
                                 Telephone No.   214/969-6563

                                 Attention:  Martin W. Wilson

                                 with a copy to:

                                 Livonia Operations Center
                                 39200 Six Mile Road, 4th Floor
                                 Livonia, Michigan 48152

                                 Telecopier:     734/632-7050
                                 Telephone No.   734/632-3063

                                 Attention:  Nancy Lee

                        [Third Amendment to Amended and
                           Restated Credit Agreement
                               Signature Page 6]

<PAGE>   12
                                       THE BANK OF NEW YORK

                                       By: /s/ Peter Keller
                                          --------------------------
                                       Name: Peter Keller
                                       Title: Vice President

                                       Applicable Lending Office for Base Rate
                                         Loans:

                                       Address:  One Wall Street
                                                 Energy Division, 19th Floor
                                                 New York, New York 10286

                                       Telecopier No.:212/635-7924
                                       Telephone No.: 212/635-7550

                                       Attention:  Kathy D'Elena

                                       Applicable Lending Office for Fixed
                                         Rate Loans:

                                       Address:  One Wall Street
                                                 Energy Division, 19th Floor
                                                 New York, New York 10286

                                       Telecopier No.:212/635-7924
                                       Telephone No.: 212/635-7550

                                       Attention:  Kathy D'Elena

                                       Address for Notices:
                                       The Bank of New York
                                       One Wall Street
                                       Energy Division, 19th Floor
                                       New York, NY  10286

                                       Telecopier No.: 212/635-7924
                                       Telephone No.:  212/635-7550

                                       Attention: Kathy D'Elena

                        [Third Amendment to Amended and
                           Restated Credit Agreement
                               Signature Page 7]

<PAGE>   13
                                            with a copy to:

                                                     Address:
                                            The Bank of New York
                                              One Wall Street
                                            Energy Division, 19th Floor
                                            New York, NY  10286

                                            Telecopier No.: 212/635-7924
                                            Telephone No.:  212/635-7861

                                            Attention: Peter Keller

                        [Third Amendment to Amended and
                           Restated Credit Agreement
                               Signature Page 8]

<PAGE>   14
                                        NATEXIS BANQUE

                                        By: /s/ N. Eric Ditges
                                           -----------------------------
                                        Name: N. Eric Ditges
                                        Title: Vice President

                                        By: /s/ Louis P. Laville, III
                                           -----------------------------
                                        Name: Louis P. Laville, III
                                        Title: Vice President and Group Manager

                                        Applicable Lending Office for Base
                                          Rate Loans:

                                        Address:  645 5th Avenue, 20th Floor
                                                  New York, New York
                                        Telecopier No.:212/872-5045

                                        Applicable Lending Office for Fixed
                                          Rate Loans:

                                        Address:  645 5th Avenue, 20th Floor
                                                  New York, New York
                                        Telecopier No.:212/872-5045

                                        Address for Notices:

                                        Natexis Banque, Southwest
                                            Representative Office
                                        333 Clay Street, Suite 4340
                                        Houston, Texas  77002
                                        Telecopier No.: 713/759-9908
                                        Telephone No.: 713/759-9401

                                        Attention:  Tanya McAllister

                                        with a copy to:

                                        Address:

                                        Natexis Banque, New York Branch
                                        645 5th Avenue, 20th Floor
                                        New York, New York
                                        Telecopier No.: 212/872-5045

                                        Attention: Joan Rankine

                        [Third Amendment to Amended and
                           Restated Credit Agreement
                               Signature Page 9]

<PAGE>   15

                                            Natexis Banque, Southwest
                                                Representative Office
                                            333 Clay Street, Suite 4340
                                            Houston, Texas  77002

                                            Telecopier No.: 713/759-9908
                                            Telephone No.: 713/759-9401

                                            Attention: Eric Ditges

                        [Third Amendment to Amended and
                           Restated Credit Agreement
                               Signature Page 10]

<PAGE>   16
                                       BANK ONE, TEXAS, N.A.

                                       By: /s/ Christine M. Macan
                                       -----------------------------------------
                                       Name: Christine M. Macan
                                       Title: Vice President

                                       Applicable Lending Office for Base
                                         Rate Loans:

                                       Address:   910 Travis, TX2-4330
                                                  Houston, Texas 77002

                                       Applicable Lending Office for Fixed
                                         Rate Loans:

                                       Address:   910 Travis, TX2-4330
                                                  Houston, Texas 77002

                                       Address for Notices:

                                       Bank One Center
                                       910 Travis, TX2-4330
                                       Houston, Texas 77002

                                       Telecopier No.: 713/751-3544
                                       Telephone No.: 713/751-3484

                                       Attention: Christine Macan

                                       with a copy to:

                                       Address:   Bank One Center
                                                  910 Travis, TX2-4375
                                                  Houston, Texas 77002

                                       Telecopier No.: 713/751-3982
                                       Telephone No.:  713/751-6174

                                       Attention:  Jeanie Harman

                                      and

                        [Third Amendment to Amended and
                           Restated Credit Agreement
                               Signature Page 11]

<PAGE>   17
                                      Address:   500 Throckmorton
                                                 West Complex PG6
                                                 Fort Worth, Texas 76102

                                      Telecopier No.: 817/884-4651
                                      Telephone No.:  817/884-4399

                                      Attention:  Carol Peacock

                        [Third Amendment to Amended and
                           Restated Credit Agreement
                               Signature Page 12]

<PAGE>   18
                                       HIBERNIA NATIONAL BANK

                                       By: /s/ David R. Reid
                                       -----------------------------------------
                                       Name: David R. Reid
                                       Title: Senior Vice President

                                       Applicable Lending Office for Base
                                         Rate Loans:

                                       Address:   313 Carondelet Street
                                                  New Orleans, Louisiana 70130

                                       Applicable Lending Office for Fixed
                                         Rate Loans:

                                       Address:   313 Carondelet Street
                                                  New Orleans, Louisiana 70130

                                       Address for Notices:

                                       213 W. Vermilion
                                       Lafayette, Louisiana 70501

                                       Telecopier No.: 318/268-4566
                                       Telephone No.:  318/268-4582

                                       Attention: David Reid

                                       with a copy to:

                                       Address:   313 Carondelet Street
                                                  New Orleans, Louisiana 70130

                                       Telecopier No.: 504/533-5434
                                       Telephone No.:  504/533-5717

                                       Attention: Spencer Gagnet

                        [Third Amendment to Amended and
                           Restated Credit Agreement
                               Signature Page 13]

                                      and

<PAGE>   19
                                        Address:  313 Carondelet Street
                                                  New Orleans, Louisiana 70130

                                        Telecopier No.: 504/533-5434
                                        Telephone No.:  504/533-5352

                                        Attention: Virginia Bell Cowart

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