Document:

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                                                                   Exhibit 10.19

                               FOURTH AMENDMENT TO
                           REVOLVING CREDIT AGREEMENT

         THIS FOURTH AMENDMENT TO REVOLVING CREDIT AGREEMENT (the "Amendment")
is made and entered into as of the 3rd day of May, 2002 (the "Effective Date"),
by and among XTO ENERGY INC. (successor by name change to Cross Timbers Oil
Company), a Delaware corporation ("Company"), the Banks that are signatories
hereto (collectively, the "Banks"), JP MORGAN CHASE BANK (successor by merger to
Morgan Guaranty Trust Company of New York), as Administrative Agent for Banks,
BANK OF AMERICA, N.A., as Syndication Agent for Banks, JP MORGAN CHASE BANK
(successor by merger to The Chase Manhattan Bank), as Documentation Agent for
Banks, and FLEET NATIONAL BANK, as Co-Documentation Agent for Banks.

                              W I T N E S S E T H:
                              - - - - - - - - - -

         WHEREAS, Company, JPMorgan Chase Bank (successor by merger to Morgan
Guaranty Trust Company of New York), as Administrative Agent for Banks, Bank of
America N.A., as Syndication Agent for Banks, JPMorgan Chase Bank (successor by
merger to The Chase Manhattan Bank), as Documentation Agent for Banks, Fleet
National Bank, as Co-Documentation Agent for Banks, and Banks have entered into
that certain Revolving Credit Agreement dated as of May 12, 2000 (as amended by
that certain First Amendment to Revolving Credit Agreement dated as of June 20,
2000 among Company and Banks, as amended by that certain Second Amendment to
Revolving Credit Agreement dated as of February 16, 2001 among Company and
Banks, as amended by that certain Third Amendment to Revolving Credit Agreement
dated as of May 1, 2001 among Company and Banks, as amended hereby and as
amended from time to time hereafter, the "Loan Agreement").

         WHEREAS, the parties hereto desire to amend the Loan Agreement as set
forth herein.

         NOW, THEREFORE, in consideration of the premises herein contained and
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the parties, intending to be legally bound, agree as
follows:

                                    ARTICLE I
                           Definitions and References

         1.01     Unless otherwise specifically defined herein, each term used
herein which is defined in the Loan Agreement as in effect immediately prior to
the Effective Date shall have the meaning assigned to such term in the Loan
Agreement as so in effect. Each reference to "hereof," "hereunder," "herein" and
"hereby" and each other similar reference and each reference to "this Loan
Agreement" and each

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other similar reference contained in the Loan Agreement shall from and after the
Effective Date refer to the Loan Agreement as amended hereby.

                                   ARTICLE II
                                   Amendments

         2.01.    Amendment to Article I; Amendment to Certain Defined Terms.
Effective as of the Effective Date, (i) the defined term "Obligation" is amended
by inserting the phrase "or the Senior Debt," following the phrase "or the
Subordinated Indebtedness" as such phrase appears in such definition and (ii)
sub-part (xiii)(b) of the defined term "Permitted Liens" is amended by deleting
the amount "$15,000,000" as it appears in such sub-part and substituting the
amount "$40,000,000" therefor.

         2.02.    Amendment to Section 2.01. Effective as of the Effective Date,
sub-part (d) of Section 2.01 of the Loan Agreement is amended by deleting the
period at the end of such sub-part (d) and adding thereto the following:

         "and (vi) to prepay or redeem Subordinated Indebtedness in accordance
         with the last sentence of Section 9.19."

         2.03.    Amendment to Section 9.01. Effective as of the Effective Date,
sub-part (xii) of Section 9.01 of the Loan Agreement is amended and restated in
its entirety as follows:

         "Indebtedness of the Company and the Subsidiaries (in the aggregate)
         incurred subsequent to May 1, 2002, and not otherwise permitted
         hereunder, not exceeding $25,000,000 at any one time outstanding
         exclusive of any Indebtedness between Company and the Subsidiaries,"

         2.04.    Amendment to Section 9.19. Effective as of the Effective Date,
Section 9.19 of the Loan Agreement is amended by deleting the last sentence in
Section 9.19 and substituting the following sentence therefor:

         "Notwithstanding the foregoing, provided that no Event of Default
         exists or will occur as a result of the actions taken by Company
         permitted hereby and no Borrowing Base Deficiency exists, without the
         prior consent of Banks, after January 1, 2002, Company may prepay or
         redeem (with or without a premium and in whole or in part) the
         Subordinated Indebtedness under the April 1997 Indenture and/or the
         October 1997 Indenture."

                                   ARTICLE III
                               Condition Precedent

         3.01.    Counterparts; Conditions to Effectiveness. This instrument
shall become effective (and the Loan Agreement shall be amended with the
amendments referred to herein) as of the Effective Date when Administrative
Agent shall have received a duly executed counterpart hereof signed by Company
and Majority

                                       2

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Banks (or, in the case of any Bank included within Majority Banks as to which an
executed counterpart shall not have been received, Administrative Agent shall
have received telegraphic, telex or other written confirmation from such party
of execution of a counterpart hereof by such Bank).

         3.02.    Amendment Fee. Upon Administrative Agent's receipt of duly
executed counterparts hereof signed by Company and Majority Banks, Company shall
pay to Administrative Agent a fee in the amount $2,500 for each Bank that has
executed a counterpart of this Amendment and delivered such counterpart of this
Amendment to Administrative Bank on or before May 3, 2002. Administrative Agent
shall distribute such fee to such Banks who have executed, and delivered to
Administrative Bank on or before the prescribed date, its counterpart of this
Amendment. The fee payable under this Section 3.02 shall be paid by Company to
Administrative Agent within three (3) Business Days after Company's receipt of
Administrative Agent's written request or invoice for same.

                                   ARTICLE IV
                  Ratifications, Representations and Warranties

         4.01.    Ratifications. The terms and provisions set forth herein shall
modify and supersede all inconsistent terms and provisions set forth in the Loan
Agreement immediately before giving effect hereto and the other Loan Papers,
and, except as expressly modified, amended, and superseded herein, the terms and
provisions of the Loan Agreement and the other Loan Papers are ratified and
confirmed and shall continue in full force and effect. Company and Banks agree
that the Loan Agreement, as amended hereby, and the other Loan Papers shall
continue to be legal, valid, binding and enforceable in accordance with their
respective terms.

         4.02.    Representations, Warranties and Agreements. Company hereby
represents and warrants to Banks that (a) the execution, delivery and
performance of the Loan Agreement as amended hereby has been authorized by all
requisite corporate action on the part of Company and will not violate the
Articles/Certificate of Incorporation or Bylaws of Company; (b) the
representations and warranties contained in the Loan Agreement, as amended
hereby, and any other Loan Papers are true and correct on and as of the date
hereof and on and as of the date of execution hereof as though made on and as of
each such date; (c) no Default or Event of Default under the Loan Agreement, as
amended hereby, has occurred and is continuing; and (d) Company is in full
compliance with all covenants and agreements contained in the Loan Agreement and
the other Loan Papers, as amended hereby.

                                    ARTICLE V
                           Ratifications by Guarantors

         5.01.    Ratification by Guarantors. CT Trading and the Gas Marketing
Subsidiaries (collectively, the "Guarantors") hereby acknowledge and agree to
the

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terms hereof and hereby ratify and reaffirm all of their respective
obligations under their unconditional guaranties of the Loan and Obligation (the
"Guaranties"). Guarantors also hereby agree that nothing in this Amendment shall
adversely affect any right or remedy of Banks under the Guaranties and that the
execution and delivery of this Amendment shall in no way change or modify their
respective obligations as guarantor under the Guaranties. Although the
Guarantors have been informed by Company of the matters set forth in this
Amendment and the Guarantors have acknowledged and agreed to the same, the
Guarantors understand that Banks have no duty to notify Guarantors or to seek
Guarantors' acknowledgment or agreement, and nothing contained herein shall
create such a duty as to any transaction hereafter.

                                   ARTICLE VI
                            Miscellaneous Provisions

         6.01.    Reference to Loan Agreement. The other Loan Papers, and any
and all other agreements, documents or instruments now or hereafter executed and
delivered pursuant to the terms hereof or pursuant to the terms of the Loan
Agreement, as amended hereby, are hereby amended so that any reference in the
Loan Agreement and such other Loan Papers to the Loan Agreement shall mean a
reference to the Loan Agreement as amended hereby.

         6.02.    Expenses of Agents. As provided in the Loan Agreement, Company
agrees to pay on demand all reasonable costs and expenses incurred by Agents in
connection with the preparation, negotiation and execution of this Amendment,
including, without limitation, the costs and fees of Agent's legal counsel, and
all reasonable costs and expenses incurred by Banks in connection with the
enforcement or preservation of any rights under the Loan Agreement, as amended
hereby, or any other Loan Papers, including, without, limitation, the reasonable
costs and fees of Agents' legal counsel. Company shall not be responsible for
the cost or expense of legal counsel of any other Bank in connection with the
preparation, execution and delivery of this Amendment.

         6.03.    Counterparts. This instrument may be executed in one or more
counterparts, each of which when so executed shall be deemed to be an original,
but all of which when taken together shall constitute one and the same
instrument.

         6.04.    Headings. The headings, captions, and arrangements used herein
are for convenience only and shall not affect the interpretation of this
instrument.

         6.05.    Applicable Law. THE LOAN AGREEMENT AS AMENDED HEREBY AND ALL
OTHER LOAN PAPERS EXECUTED PURSUANT HERETO SHALL BE DEEMED TO HAVE BEEN MADE AND
TO BE PERFORMABLE IN AND SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH
THE LAWS OF THE STATE OF TEXAS UNLESS THE LAWS GOVERNING NATIONAL BANKS SHALL
HAVE APPLICATION.

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         6.06.    Final Agreement. THE LOAN AGREEMENT AS AMENDED HEREBY AND THE
OTHER LOAN PAPERS, EACH AS AMENDED HEREBY, REPRESENT THE ENTIRE EXPRESSION OF
THE PARTIES WITH RESPECT TO THE SUBJECT MATTER HEREOF ON THE EFFECTIVE DATE THIS
AMENDMENT IS EXECUTED. THE LOAN AGREEMENT AS AMENDED HEREBY AND THE OTHER LOAN
PAPERS, AS AMENDED HEREBY, MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES. THERE ARE NO
UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES. NO MODIFICATION, RESCISSION,
WAIVER, RELEASE OR AMENDMENT OF ANY PROVISION OF THE LOAN AGREEMENT OR THE OTHER
LOANS PAPERS SHALL BE MADE, EXCEPT BY A WRITTEN AGREEMENT SIGNED BY COMPANY AND
EITHER BANKS OR MAJORITY BANKS, AS PROVIDED IN THE LOAN AGREEMENT.

         IN WITNESS WHEREOF, this Amendment has been executed in multiple
originals and is effective as of the date first above-written.

                          [SIGNATURE PAGES TO FOLLOW]

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                          COMPANY:

                          XTO ENERGY COMPANY, INC.,
                          a Delaware corporation

                          By:                   JOHN O'REAR
                                --------------------------------------------
                                John O'Rear, Vice President and Treasurer

                          GUARANTORS:

                          CROSS TIMBERS TRADING COMPANY,
                          a Texas corporation

                          By:                   JOHN O'REAR
                                --------------------------------------------
                                John O'Rear, Vice President and Treasurer

                          RINGWOOD GATHERING COMPANY,
                          a Delaware corporation

                          By:                 LOUIS G. BALDWIN
                                --------------------------------------------
                                Louis G. Baldwin, Vice President and Treasurer

                          CROSS TIMBERS ENERGY SERVICES, INC.,
                          A Texas corporation

                          By:                 LOUIS G. BALDWIN
                                --------------------------------------------
                                Louis G. Baldwin, Vice President and Treasurer

                          TIMBERLAND GATHERING & PROCESSING COMPANY,
                          INC., a Texas corporation

                          By:                 LOUIS G. BALDWIN
                                --------------------------------------------
                                Louis G. Baldwin, Vice President and Treasurer

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                          BANKS:

                          JP MORGAN CHASE BANK

                          By:              ROBERT C. MORTENSOTTO
                                --------------------------------------------
                                Robert C. Mortensotto, Managing Director

                          BANK OF AMERICA, N.A.

                          By:                  RICHARD STEIN
                                --------------------------------------------
                                Richard Stein
                                Principal

                          FLEET NATIONAL BANK

                          By:               JEFFREY H. RATHKAMP
                                --------------------------------------------
                                Jeffrey H. Rathkamp
                                Vice President

                          ABN-AMRO BANK N.V., HOUSTON AGENCY

                          By:   ABN-AMRO NORTH AMERICA, INC.

                          By:                  JAMIE A. CONN
                                --------------------------------------------
                                Jamie A. Conn
                                Group Vice President

                          By:                   JOHN D. REED
                                --------------------------------------------
                                John D. Reed
                                Vice President

                          BANK ONE, NA

                          By:                   MARK CRANMER
                                --------------------------------------------
                                W. M. (Mark) Cranmer, Vice President

                                        7

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                          BNP PARIBAS

                          By:                    DAVID DODD
                                --------------------------------------------
                                David Dodd
                                Director

                          By:                   BETSY JOCHER
                                --------------------------------------------
                                Betsy Jocher
                                Vice President

                          WACHOVIA BANK, NATIONAL ASSOCIATION
                          (f/k/a First Union National Bank)

                          By:               ROBERT R. WETTEROFF
                                --------------------------------------------
                                Robert R. Wetteroff
                                Senior Vice President

                          BANK OF MONTREAL

                          By:                 JAMES V. DUCOTE
                                --------------------------------------------
                                James V. Ducote
                                Director

                          THE BANK OF NEW YORK

                          By:                RAYMOND J. PALMER
                                --------------------------------------------
                                Raymond J. Palmer
                                Vice President

                          THE BANK OF NOVA SCOTIA

                          By:                     N. BELL
                                --------------------------------------------
                                N. Bell, Senior Manager

                                        8

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                          BANK OF SCOTLAND

                          By:                  JOSEPH FRATUS
                                --------------------------------------------
                                Joseph Fratus
                                Vice President

                          COMERICA BANK-TEXAS

                          By:                 MICHELE L. JONES
                                --------------------------------------------
                                Michele L. Jones
                                Vice President

                          CREDIT LYONNAIS NEW YORK BRANCH

                          By:                BERNARD WEYMULLER
                                --------------------------------------------
                                Bernard Weymuller
                                Senior Vice President

                          FORTIS CAPITAL CORP.
                          (f/k/a MeesPierson Capital Corp.)

                          By:                 DEIRDRE SANBORN
                                --------------------------------------------
                                Deirdre Sanborn
                                Vice President

                          By:                DARRELL W. HOLLEY
                                --------------------------------------------
                                Darrell W. Holley
                                Managing Director

                          NATEXIS BANQUES POPULAIRES
                          (f/k/a NATEXIS Banque)

                          By:               DONOVAN C. BROUSSARD
                                --------------------------------------------
                                Donovan C. Broussard
                                Vice President

                          By:                RENAUD J. D'HERBES
                                --------------------------------------------
                                Renaud J. d'Herbes
                                Senior Vice President and Regional Manager

                                        9

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                          U. S. BANK NATIONAL ASSOCIATION

                          By:                 MARK E. THOMPSON
                                --------------------------------------------
                                Mark E. Thompson, Vice President

                          WELLS FARGO BANK (TEXAS), N.A.

                          By:                CHARLES D. KIRKHAM
                                --------------------------------------------
                                Charles D. Kirkham, Vice President

                          MIZUHO CORPORATE BANK, LTD.
                          (f/k/a Fuji Bank, Ltd.)

                          By:                 THOMAS W. BOYLAN
                                --------------------------------------------
                                Thomas W. Boylan
                                VP & Sr. Team Leader

                          THE FROST NATIONAL BANK

                          By:                  STEWART ALCORN
                                --------------------------------------------
                                Stewart Alcorn
                                Market President

                          SUMITOMO MITSUI BANKING CORPORATION

                          By:                 WILLIAM M. GINN
                                --------------------------------------------
                                William M. Ginn
                                General Manager

                                       10<PAGE>

                                                                   EXHIBIT 10.13

                                 FIRST AMENDMENT
                                     TO THE
                         RETRACTABLE TECHNOLOGIES, INC.
                             1999 STOCK OPTION PLAN

     This First Amendment to the RETRACTABLE TECHNOLOGIES, INC. 1999 STOCK
OPTION PLAN (the "Plan") is authorized by Thomas J. Shaw and Douglas W. Cowan,
the Chairman and Member of the Compensation and Benefits Committee (the
"Committee") of Retractable Technologies, Inc. ("Retractable"), respectively.

                                    RECITALS

     WHEREAS, Section 4 of the Plan provides that the "...Plan shall be
administered by the Committee or, in the absence of Committee, by the Board."
Section 4 further provides that "(t)he interpretation and construction of any
provision of (the) Plan by the Committee shall be final, unless otherwise
determined by the Board"; and

     WHEREAS, Section 18 of the Plan provides that "(t)he Board of Directors may
discontinue the Plan and the Committee may amend the Plan from time to time...";
and

     WHEREAS, the stockholders have authorized increasing the maximum number of
shares of stock that may be optioned or sold under this Plan from 2 million to 4
million shares effective September 20, 2002; and

     WHEREAS, federal tax laws require that incentive stock options ("ISOs") be
issued to persons not deemed to be ten percent shareholders at an exercise price
that is no less than 100% of fair market value and to be issued to persons
deemed to be ten percent shareholders at no less than 110% of fair market value;
and

     WHEREAS, the Plan currently authorizes the issuance of options to persons
not deemed to be ten percent shareholders and persons deemed to be ten percent
shareholders, respectively, at exercise prices equal to 100% and 110% of fair
market value, respectively; and

     WHEREAS, the Committee determined effective as of September 30, 2002, that
the best interests of Retractable would be served by the amendment of the Plan
to authorize the issuance of ISOs to persons not deemed to be ten percent
shareholders at an option price at least equal to 100% of fair market value of
each share and to authorize the issuance of ISOs to persons deemed to be ten
percent shareholders at an option price at least equal to 110% of the fair
market value of each share; and

     WHEREAS, Section 711 of the American Stock Exchange Company Guide provides
an exception to shareholder approval "...as a prerequisite to approval of
applications to list additional shares reserved for options granted to officers,
directors, or key employees..." where "...such options are to be granted:
....(ii) under a plan or

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arrangement for officers, directors, or key employees provided such incentive
arrangements do not authorize the issuance of more than 5% of outstanding common
stock in any one year and provided that all arrangements adopted without
shareholder approval in any five-year period do not authorize, in the aggregate,
the issuance of more than 10% of such common stock. (For the purpose of
calculating the percentage of stock issued in the aggregate, stock to be issued
pursuant to options which have expired and/or been cancelled shall not be
included.)"; and

     WHEREAS, an amendment to authorize the issuance of ISOs at or above fair
market value does not require shareholder approval; now, therefore:

                                   AMENDMENTS

     1.   Section (3) of the Plan is hereby amended and restated in its
entirety, effective as of September 20, 2002, to read as follows:

          (3) STOCK TO BE OPTIONED; DESIGNATION OF INCENTIVE STOCK OPTIONS.
          Subject to the provisions of Section (11) of this Plan, the maximum
          number of shares of Stock that may be optioned or sold under this Plan
          is Four Million (4,000,000) shares, all of which may be designated as
          ISOs. The shares shall be either treasury or authorized but unissued
          shares of Stock of the Company. Options or portions of options granted
          under this Plan to key employees may, in the discretion of the
          Committee, be designated as ISOs or NQSOs. Options granted to
          non-employees must be NQSOs. In addition to any other term or
          provision of this Plan applicable to an ISO, any option designated as
          an ISO shall also be subject to the condition that the aggregate fair
          market value (determined at the time the options are granted) of the
          Company's Common Stock with respect to which incentive stock options
          are exercisable for the first time by any individual employee during
          any calendar year (under this Plan and all other similar plans of the
          Company and its subsidiaries hereafter adopted) shall not exceed One
          Hundred Thousand Dollars ($100,000.00).

     2.   Section (6) of the Plan is hereby amended and restated in its
entirety, effective as of September 30, 2002, to read as follows:

          (6) OPTION PRICE FOR ISOs AND NQSOs. For any Participant who is not
          deemed to be a Ten Percent (10%) Shareholder under the rules
          applicable to ISOs under 422 of the Code (a "10% Shareholder"), the
          Option Price for each share to be acquired pursuant to an ISO shall be
          at least One Hundred Percent (100%) of the fair market value of the
          share as determined by the Board of Common Stock on the date the ISO
          is granted. For any Participant who is deemed to be a 10% Shareholder
          under the rules applicable to ISOs under Section 422 of the Code, the
          Option Price for each share to be acquired pursuant to an ISO shall be
          at least One Hundred Ten Percent (110%) of the fair market value of
          the share. The

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          Option Price for any NQSO shall be as determined by the Board of
          Common Stock on the date the NQSO is granted. In addition, the Board
          shall include in any NQSO granted pursuant to this Plan a condition
          that, upon exercise of the NQSO and prior to the issuance of any stock
          certificate to the Participant, the Participant shall remit to the
          Company the amount, if any, of any federal, state, or local employment
          taxes required to be withheld upon exercise of the NQSO. The
          Participant may (i) make a direct payment to the Company to satisfy
          this obligation, (ii) increase withholding on his cash compensation on
          the date the NQSO is exercised, and/or (iii) use the procedure
          described in the following provisions of this Section (6). One (1)
          month prior to exercise of a NQSO, the Participant may deliver a
          notice of withholding election to the Company. The notice shall state
          that the Company is to (i) calculate the amount of withholding tax due
          as if all shares for which a NQSO is to be exercised were delivered,
          (ii) reduce that number of shares made available for delivery so that
          the fair market value of the shares withheld on the exercise date
          approximates the Company's withholding tax obligation, and (iii) pay
          the cash to the Internal Revenue Service and other applicable taxing
          authorities on the Participant's behalf instead. No withholding
          obligation shall be imposed by this Section (6) unless also imposed by
          applicable law.

  /s/ Thomas J. Shaw                          /s/ Douglas W. Cowan
--------------------------------------      ------------------------------------
Thomas J. Shaw, Chairman                    Douglas W. Cowan, Member
Compensation and Benefits Committee         Compensation and Benefits Committee

Executed this March 31, 2003, to reflect amendments to the 1999 Stock Option
Plan made in September, 2002.

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