QuickLinks -- Click here to rapidly navigate through this document

Exhibit 10.28

TENTH AMENDMENT TO LOAN AGREEMENT AND
AMENDMENT TO INTERCREDITOR AGREEMENT

        THIS TENTH AMENDMENT TO LOAN AGREEMENT AND AMENDMENT TO INTERCREDITOR
AGREEMENT (herein called this "Amendment") is made as of the 3rd day of January,
2003, by and among Western Gas Resources, Inc. ("Borrower"), Bank of America,
N.A. ("Agent"), and the Lenders under the Loan Agreement referred to below.

W I T N E S S E T H:

        WHEREAS, Borrower, Agent, and Lenders have entered into that certain
Loan Agreement dated as of April 29, 1999 (as amended, restated, or supplemented
to the date hereof, the "Original Agreement"), for the purposes and
consideration therein expressed, pursuant to which Lenders made and became
obligated to make loans to Borrower as therein provided;

        WHEREAS, Borrower, Agent, and Lenders desire to amend the Original
Agreement for the purposes described herein;

        WHEREAS, Borrower previously issued to The Prudential Insurance Company
of America ("PICA") and Pruco Life Insurance Company ("PRUCO") those certain
Senior Notes dated October 27, 1992, September 22, 1993, December 27, 1993,
October 27, 1994, and July 28, 1995, pursuant to a Master Shelf Agreement dated
as of December 19, 1991 by and between Borrower and PICA (as heretofore amended,
supplemented or modified, the "Original Prudential Agreement");

        WHEREAS, Borrower is entering into a Third Amended and Restated Master
Shelf Agreement dated as of December 19, 1991 (effective as of January 13, 2003)
(the "Restated Prudential Agreement"), with PICA, PRUCO and Prudential
Investment Management, Inc. ("Prudential"), amending and restating the Original
Prudential Agreement, pursuant to which, among other things, the period during
which senior notes may be issued thereunder is being extended and the facility
size is being increased by $65,000,000 (allowing Borrower to issue an additional
$65,000,000 in Debt Securities);

        WHEREAS, Agent, Lenders, and Prudential (as successor in interest to
PICA) entered into that certain Intercreditor Agreement dated as of April 26,
2001 (the "Original Intercreditor Agreement"), to evidence their agreement with
respect to certain payments that may be received by the Lenders and PICA under
or in connection with the various guaranties executed by Related Persons in
favor of the Lenders and Prudential;

        WHEREAS, Prudential is succeeding to all of PICA's rights and
obligations under the Original Intercreditor Agreement;

        WHEREAS, Borrower desires that Majority Lenders consent to the Restated
Master Shelf Agreement and the terms set forth therein; and

        WHEREAS, Agent, Lenders and Prudential desire to amend the Original
Intercreditor Agreement on the terms set forth herein.

        NOW, THEREFORE, in consideration of the premises and the mutual
covenants and agreements contained herein and in the Original Agreement, in
consideration of the loans which may hereafter be made by Lenders to Borrower,
and for other good and valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, the parties hereto do hereby agree as follows:

ARTICLE I.
Definitions and References

        § 1.1.    Defined Terms.    Unless the context otherwise requires or
unless otherwise expressly defined herein, the terms defined in the Original
Agreement shall have the same meanings whenever used in this Amendment. As used
herein, the following terms shall have the following meanings:

        "Amendment" means this Tenth Amendment to Loan Agreement and Amendment
to Intercreditor Agreement.

        "Intercreditor Agreement" means the Original Intercreditor Agreement as
amended by this Amendment.

        "Loan Agreement" means the Original Agreement as amended by this
Amendment.

ARTICLE II.
Amendment

        § 2.1.    Definitions.    

        (a)  The definition of "Debt Securities" in Section 1.1 of the Original
Agreement is hereby amended in its entirety to read as follows:

        "Debt Securities" means collectively those senior notes dated
October 27, 1992, September 22, 1993, December 27, 1993, October 27, 1994,
July 28, 1995, and all other senior notes issued by Borrower pursuant to that
certain Third Amended and Restated Master Shelf Agreement effective as of
January 13, 2003, between Borrower and The Prudential Insurance Company of
America, Prudential Investment Management, Inc., Pruco Life Insurance Company
and certain Prudential Affiliates, their successors and assigns, as amended,
supplement, modified and restated from time to time (herein called the "Shelf
Agreement")."

        (b)  The following definitions are hereby added to Section 1.1 of the
Original Agreement, in alphabetical order, to read as follows:

        "Assignment and Acceptance" means an assignment and acceptance in
substantially the same form as Exhibit G."

        "Tranche A Lenders" means Lenders designated as Tranche A Lenders on the
Lenders Schedule."

        "Tranche A Majority Lenders" means, at the time in question, two or more
Tranche A Lenders collectively having at least a 662/3% Tranche A Percentage
Share."

        "Tranche A Percentage Share" means, with respect to any Tranche A Lender
(a) when used in Sections 2.1 or 2.9, in any Notice of Borrowing or when no
Tranche A Loans are outstanding hereunder, the percentage set forth opposite
such Tranche A Lender's name on Schedule 3 attached hereto, and (b) when used
otherwise, the percentage equal to the percentage obtained by dividing (i) the
sum of the unpaid principal balance of such Tranche A Lender's Tranche A Loans
at the time in question, by (ii) the aggregate unpaid principal balance of all
Tranche A Loans at such time."

        "Tranche B Lenders" means Lenders designated as Tranche B Lenders on the
Lenders Schedule."

        "Tranche B Majority Lenders" means, at the time in question, two or more
Tranche B Lenders collectively having at least a 662/3% Tranche B Percentage
Share."

        "Tranche B Percentage Share" means, with respect to any Tranche B Lender
(a) when used in Sections 2.1 or 2.9, in any Notice of Borrowing or when no
Tranche B Loans are outstanding hereunder, the percentage set forth opposite
such Tranche B Lender's name on Schedule 3 attached hereto, and (b) when used
otherwise, the percentage equal to the percentage obtained by dividing (i) the
sum of the unpaid principal balance of such Tranche B Lender's Tranche B Loans
at the time in question plus the Matured LC Obligations which such Tranche B
Lender has funded pursuant to Section 3.2(b) plus that portion of the amount
which Tranche B Lenders might be called upon to advance under all LCs then
outstanding that such Tranche B Lender would be obligated to fund under
Section 3.2(b), by (ii) the aggregate unpaid principal balance of all Tranche B
Loans at such time plus the aggregate amount of LC Obligations outstanding at
such time."

        § 2.2.    Committed Loans.    Section 2.1 of the Original Agreement is
hereby amended in its entirety to read as follows:

        "Section 2.1    Committed Loans.    

        (a)    Tranche A Loans.    Subject to the terms and conditions hereof,
Tranche A Lenders severally agree to make loans to Borrower (herein called such
Tranche A Lender's "Tranche A Loans") from time to time on any Business Day
during the Tranche A Commitment Period so long as (i) all Tranche A Lenders are
requested to make Tranche A Committed Loans of the same Type in accordance with
their respective Tranche A Percentage Shares and as part of the same Borrowing,
(ii) the aggregate amount of all Tranche A Loans outstanding does not exceed the
Tranche A Commitment at any time and (iii) the aggregate amount of all Loans
(including Committed Loans and Competitive Bid Loans) and all LC Obligations
does not exceed the Commitment. The aggregate amount of all Tranche A Loans in
any Borrowing must be greater than or equal to $250,000 and must be a higher
integral multiple of $100,000 or must equal the unadvanced portion of the
Tranche A Commitment. The obligation of Borrower to repay to each Tranche A
Lender the aggregate amount of all Tranche A Loans made by such Tranche A
Lender, together with interest accruing in connection therewith, shall be
evidenced by a single promissory note made by Borrower payable to the order of
such Tranche A Lender (herein called such Tranche A Lender's "Tranche A Note")
in the form of Exhibit A with appropriate insertions. The amount of principal
owing on any Tranche A Lender's Tranche A Note at any given time shall be the
aggregate amount of all Tranche A Loans theretofore by such Tranche A Lender
made minus all payments of principal theretofore received by such Tranche A
Lender on its Tranche A Note. Principal paid or prepaid on the Tranche A Notes
may, subject to the terms and conditions hereof, be reborrowed during the
Tranche A Commitment Period. Interest on each Tranche A Note shall accrue and be
payable as provided herein and therein.

        (b)    Tranche B Loans.    Subject to the terms and conditions hereof,
Tranche B Lenders severally agree to make loans to Borrower (herein called such
Tranche B Lender's "Tranche B Loans") from time to time on any Business Day
during the Tranche B Commitment Period so long as (i) all Tranche B Lenders are
requested to make Tranche B Loans of the same Type in accordance with their
respective Tranche B Percentage Shares and as part of the same Borrowing,
(ii) the sum of (a) the aggregate amount of all Tranche B Loans outstanding plus
(b) the LC Obligations outstanding does not exceed the Tranche B Commitment at
any time and (iii) the aggregate amount of all Loans (including Committed Loans
and Competitive Bid Loans) and all LC Obligations does not exceed the
Commitment. The aggregate amount of all Tranche B Loans in any Borrowing must be
greater than or equal to $250,000 and must be a higher integral multiple of
$100,000 or must equal the unadvanced portion of the Tranche B Commitment. In
addition to the foregoing, upon the making of each payment by the Issuing Bank
pursuant to any LC, Borrower shall be deemed to have requested each Tranche B
Lender to, and such Tranche B Lender shall, make a Tranche B Loan in the amount
of such Tranche B Lender's Tranche B Percentage Share of Borrower's consequent
reimbursement obligation and apply the proceeds thereof to the payment of such
reimbursement obligation. When any Matured LC Obligations is repaid with
proceeds of a Borrowing, such Matured LC Obligations so repaid shall be
extinguished and such Borrowing shall be governed by the terms of this Agreement
applicable to all other Borrowings. Any such Borrowings are Borrowings of
Committed Base Rate Loans unless otherwise designated by Borrower in compliance
with the notice requirements set forth in Section 2.2. The obligation of
Borrower to repay to each Tranche B Lender the aggregate amount of all Tranche B
Loans made by such Tranche B Lender, together with interest accruing in
connection therewith, shall be evidenced by a single promissory note made by
Borrower payable to the order of such Tranche B Lender (herein called such
Tranche B Lender's "Tranche B Note") in the form of Exhibit B with appropriate
insertions. The amount of principal owing on any Tranche B Lender's Tranche B
Note at any given time shall be the aggregate amount of all Tranche B Loans
theretofore by such Tranche B Lender made minus all payments of principal
theretofore received by such Tranche B Lender on its Tranche B Note. Principal
paid or prepaid on the Tranche B Notes may, subject to the terms and conditions
hereof, be reborrowed during the Tranche B Commitment Period. Interest on each
Tranche B Note shall accrue and be payable as provided herein and therein."

        § 2.3.    Mandatory Prepayments.    Sections 2.7(a) and 2.7(b) of the
Original Agreement are hereby amended in their entirety to read as follows:

        "(a)    Tranche A Loans.    If the aggregate unpaid principal balance of
the Tranche A Loans ever exceeds the Tranche A Commitment, Borrower shall,
immediately after Agent on behalf of Tranche A Majority Lenders gives written
notice of such fact to Borrower, make a prepayment to Agent for distribution to
Tranche A Lenders in the amount of such excess on the Tranche A Loans in
accordance with Tranche A Lenders' Tranche A Percentage Shares.

        (b)    Tranche B Loans.    If the sum of (i) the aggregate unpaid
principal balance of the Tranche B Loans and (ii) the LC Obligations outstanding
ever exceeds the Tranche B Commitment, Borrower shall, immediately after Agent
on behalf of Tranche B Majority Lenders give written notice of such fact to
Borrower, make a prepayment to Agent for distribution to Tranche B Lenders in
the amount of such excess on the Tranche B Loans in accordance with Tranche B
Lenders' Tranche B Percentage Shares and/or, if applicable, deliver LC
Collateral as required by Section 3.8."

        § 2.4.    Facility Fees.    Section 2.9 of the Original Agreement is
hereby amended in its entirety to read as follows:

        "Section 2.9    Facility Fees.    In consideration of Lenders'
commitment to enter into this Agreement and to advance funds to Borrower
hereunder, (i) Borrower will pay to Agent, for pro rata distribution to each
Tranche A Lender in accordance with its Tranche A Percentage Share, a facility
fee for Tranche A Commitment determined on a daily basis by applying the Tranche
A Facility Fee Rate to the Tranche A Commitment, and (ii) Borrower will pay to
Agent for pro rata distribution to each Tranche B Lender in accordance with its
Tranche B Percentage Share, a facility fee for the Tranche B Commitment
determined on a daily basis by applying the Tranche B Facility Fee Rate to the
Tranche B Commitment. Promptly at the end of each Fiscal Quarter Agent shall
calculate the facility fees then due and shall notify Borrower thereof. Borrower
shall pay such facility fee to Agent within five Business Days after receiving
such notice."

        § 2.5.    LCs.    Article III of the Original Agreement is hereby
amended in its entirety to read as follows:

"ARTICLE III

        Section 3.1.    LCs.    From time to time during the Tranche B
Commitment Period, Borrower may request Issuing Bank to issue, in reliance on
the agreements of Tranche B Lenders set forth in Section 3.2(b), letters of
credit (each herein called an "LC") by means of an application in the form of
Exhibit C, appropriately completed and with a proposed form of LC attached.
Issuing Bank shall have no obligation whatsoever to issue any such requested LC,
but any such LC which Issuing Bank does issue shall be subject to all terms and
provisions hereof relating to LCs, and shall be subject to the following
restrictions: (a) no LC issued hereunder shall have an expiration date later
than the earlier of two years after the date of issuance thereof or the end of
the Tranche B Commitment Period, without the prior written consent of all
Tranche B Lenders; (b) no LC issued hereunder shall be issued in an amount
greater than $10,000,000 without the prior written consent of Tranche B Majority
Lenders; (c) the LC Obligations outstanding shall at no time exceed the LC
Sublimit; (d) the sum of (i) the LC Obligations outstanding and (ii) the
aggregate amount of all Tranche B Loans does not exceed the Tranche B
Commitment; and (e) the aggregate amount of all Loans (including Committed Loans
and Competitive Bid Loans) and all LC Obligations does not exceed the
Commitment.

        Section 3.2.    Reimbursement of LCs.    

        (a)    Reimbursement by Borrower.    Each payment by Issuing Bank
pursuant to any LC (whether in response to a draft, a demand for payment, or
otherwise), shall constitute a loan to and an obligation of Borrower. Borrower
hereby promises to pay to Issuing Bank, or to Issuing Bank's order, at Issuing
Bank's office at 901 Main Street, Dallas, Texas, on demand, any and all amounts
paid by Issuing Bank pursuant to any and all LCs (such amounts being herein
called the "Matured LC Obligations"). Section 2.1(b) describes certain
situations in which such payments may be made with funds advanced by Tranche B
Lenders under the Tranche B Notes, but Borrower's obligations to pay the Matured
LC Obligations as provided in this section are absolute and not contingent upon
the conditions for such Borrowings being met. Borrower hereby promises to pay to
Issuing Bank, or to Issuing Bank's order, at Issuing Bank's office at 901 Main
Street, Dallas, Texas, on demand, interest at the Default Rate on (a) any
outstanding Matured LC Obligations and (b) any fees or other amounts due with
respect to LCs (to the extent the same can legally bear interest). Borrower
hereby promises to pay, when due, all present and future taxes, levies, costs
and charges whatsoever imposed, assessed, levied or collected on, under or in
respect of this Agreement or any LC and any payments of principal, interest or
other amounts made on or in respect of any thereof (excluding, however, any such
taxes, levies, costs and charges imposed on or measured by the overall net
income of Issuing Bank). Borrower promises to indemnify Issuing Bank against,
and to reimburse Issuing Bank on demand for, any of the foregoing taxes, levies,
costs or charges paid by Issuing Bank and any loss, liability, claim or expense,
including interest, penalties and legal fees, that Issuing Bank may incur
because of or in connection with the failure of Borrower to make any such
payment of taxes, levies, costs or charges when due or any payment of Matured LC
Obligations when due. In addition, and without limiting the generality of the
foregoing, if any law, regulation or the interpretation thereof by any court or
administrative or governmental authority shall either impose, modify or deem
applicable any capital, reserve, insurance premium or similar requirement
against letters of credit issued by Issuing Bank and the result thereof shall be
to increase the cost to Issuing Bank of issuing or maintaining any letter of
credit; then, on demand by Issuing Bank, Borrower further promises to pay to
Issuing Bank, from time to time, additional amounts which shall be sufficient to
compensate Issuing Bank for the portion of such increased costs allocable to the
LCs. A written advice(s) setting forth in reasonable detail such costs incurred
by Issuing Bank, submitted by Issuing Bank to Borrower from time to time, shall
be conclusive, absent manifest error, as to the amount thereof.

        (b)    Reimbursement by Tranche B Lenders.    Issuing Bank irrevocably
agrees to grant and hereby grants to each Tranche B Lender, and, to induce
Issuing Bank to issue LCs hereunder, each Tranche B Lender irrevocably agrees to
accept and purchase and hereby accepts and purchases from Issuing Bank, on the
terms and conditions hereinafter stated, for such Tranche B Lender's own account
and risk an undivided interest equal to such Tranche B Lender's Tranche B
Percentage Share of Issuing Bank's obligations and rights under each LC issued
hereunder and the amount of each draft paid by Issuing Bank thereunder. In the
event that Borrower should fail to pay Issuing Bank on demand the amount of any
draft or other request for payment drawn under or purporting to be drawn under a
LC as provided in subsection (a) above, each Tranche B Lender shall, before
2:00 p.m. (Dallas Time) on the Business Day Issuing Bank shall have given notice
to Tranche B Lenders of Borrower's failure to so pay Issuing Bank, if such
notice is given by 10:00 am., Dallas Time (or on the Business Day immediately
succeeding the day such notice is given after 10:00 am. Dallas Time), pay to
Issuing Bank at Issuing Bank's offices in Dallas, Texas, in legal tender of the
United States of America, in same day funds, such Tranche B Lender's Tranche B
Percentage Share of the amount of such draft or other request for payment from
Borrower plus interest on such amount from the date Issuing Bank shall have paid
such draft or request for payment to the date of such payment by such Tranche B
Lender at the Default Rate. Each Tranche B Lender's obligation to make payment
to Issuing Bank pursuant to the terms of this Section 3.2(b) is irrevocable and
unconditional. If any such amount required to be paid by any Tranche B Lender
pursuant to this Section 3.2(b) is not in fact made available by such Tranche B
Lender to Issuing Bank within three Business Days after the date such payment is
due, Issuing Bank shall be entitled to recover from such Tranche B Lender, on
demand, such amount with interest thereon calculated from such due date at the
Default Rate. A written advice(s) setting forth in reasonable detail the amounts
owing under this Section 3.2, submitted by Issuing Bank to Borrower from time to
time, shall be conclusive, absent manifest error, as to the amounts thereof.
Whenever, at any time after Issuing Bank has made payment under any LC, and has
received from any Tranche B Lender its Tranche B Percentage Share of such
payment in accordance with this Section 3.2(b), Issuing Bank receives any
payment related to such LC (whether directly from Borrower or otherwise,
including proceeds of collateral applied thereto by Issuing Bank), or any
payment of interest on account thereof, Issuing Bank will distribute to such
Tranche B Lender its Tranche B Percentage Share thereof; provided, however, that
in the event that any such payment received by Issuing Bank shall be required to
be returned by Issuing Bank, such Tranche B Lender shall return to Issuing Bank
the portion thereof previously distributed by Issuing Bank to it.

        Section 3.3.    Transferees of LCs.    Borrower agrees that if any LC
provides that it is transferable, Issuing Bank is under no duty to determine the
proper identity of anyone appearing as transferee of such LC, nor shall Issuing
Bank be charged with responsibility of any nature or character for the validity
or correctness of any transfer or successive transfers. Payment by Issuing Bank
to any purported transferee or transferees as determined by Issuing Bank is
hereby authorized and approved, and Borrower further agrees to hold Issuing Bank
and each Tranche B Lender harmless and indemnified against any liability or
claim in connection with or arising out of the foregoing or the circumstances
described in Section 3.6.

        Section 3.4.    Extension of Maturity of LCs.    Borrower agrees that in
the event of any extension of the maturity or time for presentation of drafts or
demands for payment or any other modification of the terms of any LC at the
request of Borrower or by order of any court or tribunal, with or without
notification to others, or in the event of any increase in the amount of any LC
at the request of Borrower or by order of any court or tribunal, this Agreement
shall be binding upon Borrower with respect to the LC so increased or otherwise
modified, with respect to drafts and demands for payment thereunder, and with
respect to any action taken in accordance with such extension, increase or other
modification by Issuing Bank or by any bank which is a confirming bank or an
advising bank with respect to any LC.

        Section 3.5.    Restriction on Liability.    Neither Issuing Bank nor
any bank which is a confirming bank or an advising bank with respect to an LC
(in this section called a "correspondent") shall be responsible for (a) the use
which may be made of any LC or for any acts or omissions of the users of any LC;
(b) the existence or nonexistence of a default under any instrument secured or
supported by any LC or any other event which gives rise to a right to call upon
any LC; (c) the validity, sufficiency or genuineness of any document delivered
in connection with any LC, even if such documents should in fact prove to be in
any or all respects invalid, fraudulent or forged; (d) except as specifically
required by an LC, failure of any instrument to bear any reference or adequate
reference to any LC, or failure of documents to accompany any draft at
negotiation or failure of any person to note the amount of any draft on the
reverse of any LC or surrender or take up any LC; or (e) errors, omissions,
interruptions or delays in transmission or delivery of any messages by mail,
cable, telegraph, wireless or otherwise. Issuing Bank shall not be responsible
for any act, error, neglect or default, omission, insolvency or failure in the
business of any of the correspondents or any refusal by Issuing Bank or any of
the correspondents to pay or honor drafts drawn under any LC because of any
applicable law, decree or edict, legal or illegal, of any governmental agency
now or hereafter enforced or for any matter beyond the control of Issuing Bank.
The happening of any one or more of the contingencies referred to in the
preceding clauses of this paragraph shall not affect, impair or prevent the
vesting of any of the rights or powers of Issuing Bank and Tranche B Lenders
under this Agreement, or the obligation of Borrower to make reimbursement. In
furtherance and extension and not in limitation of the specific provisions
hereinabove set forth Borrower agrees that any action taken or omitted to be
taken by Issuing Bank or any Tranche B Lender or by any correspondent under or
in connection with any LC shall be binding on Borrower and shall not put Issuing
Bank or any Tranche B Lender or any correspondent under any resulting liability
to Borrower unless grossly negligent or in breach of good faith.

        Section 3.6.    No Duty to Inquire.    Borrower agrees that Issuing Bank
is authorized and instructed to accept and pay drafts and demands for payment
under the LCs without requiring, and without responsibility for, either at the
time of acceptance or payment or thereafter, the determination as to the
existence of any event giving rise thereto or the proper identity or authority
of anyone appearing on behalf of the beneficiary of any LC.

        Section 3.7.    LC Fees.    In consideration of any issuance by Issuing
Bank of LCs hereunder and of Tranche B Lender's incurrence of a reimbursement
obligation with respect to such LCs, Borrower agrees to pay (a) to Agent for pro
rata distribution to each Tranche B Lender in accordance with its Tranche B
Percentage Share, a letter of credit fee at a rate equal to the Tranche B
Eurodollar Spread then in effect, and (b) to such Issuing Bank for its own
account, a letter of credit fronting fee at a rate equal to one-eighth of one
percent per annum in each case times the actual daily maximum amount available
to be drawn under each Letter of Credit. Such fee for each Letter of Credit
shall be due and payable on the last Business Day of each Fiscal Quarter,
commencing with the first such date to occur after the issuance of such letter
of Credit, and on the expiration date for such Letter of Credit. Any change in
the letter of credit fee rate as a result of a change in the Debt to
Capitalization Ratio or Senior Debt to Capitalization Ratio shall become
effective on the fifth Business Day following the date on which a notice is
given to Agent pursuant to Section 2.17 or Lenders otherwise become aware of
such a change in the Debt to Capitalization Ratio or the Senior Debt to
Capitalization Ratio.

        Section 3.8.    LC Collateral.    

        (a)    Cash Collateralize.    Upon the request of Agent, (i) if LC
Issuer has honored any full or partial drawing request under any Letter of
Credit and such drawing has resulted in an extension of credit resulting from
such drawing which has not been reimbursed on the date when made or refinanced
as a Borrowing, or (ii) if, as of the seventh day prior to the Tranche B
Maturity Date, any Letter of Credit remains outstanding and partially or wholly
undrawn, the Borrower shall immediately pay to LC Issuer an amount equal to the
LC Obligations then outstanding with respect to such Letter of Credit. LC Issuer
will hold such amount as security for the remaining LC Obligations (all such
amounts held as security for LC Obligations being herein collectively called "LC
Collateral") and the other Obligations, and such collateral may be applied from
time to time to any Matured LC Obligations or other Obligations which are due
and payable. Neither this subsection nor the following subsection shall,
however, limit or impair any rights which LC Issuer may have under any other
document or agreement relating to any LC, LC Collateral or LC Obligation,
including any LC Application, or any rights which any Lender Party may have to
otherwise apply any payments by Borrower and any LC Collateral hereunder.

        (b)    Acceleration of LC Obligations.    If the Obligations or any part
thereof become immediately due and payable pursuant to Section 8.1 then, unless
Tranche B Majority Lenders otherwise specifically elect to the contrary (which
election may thereafter be retracted by Tranche B Majority Lenders at any time),
all LC Obligations shall become immediately due and payable without regard to
whether or not actual drawings or payments on the LC's have occurred, and
Borrower shall be obligated to pay to LC Issuer immediately an amount equal to
the aggregate LC Obligations which are then outstanding.

        (c)    Investment of LC Collateral.    Pending application thereof, all
LC Collateral shall be invested by LC Issuer in such investments as LC Issuer
may choose in its sole discretion. All interest on (and other proceeds of) such
investments shall be reinvested or applied to Matured LC Obligations or other
Obligations which are due and payable. When all Obligations have been satisfied
in full, including all LC Obligations, all LC's have expired or been terminated,
and all of Borrower's reimbursement obligations in connection therewith have
been satisfied in full, LC Issuer shall release any remaining LC Collateral.
Borrower hereby assigns and grants to LC Issuer a continuing security interest
in all LC Collateral paid by it to LC Issuer, all investments purchased with
such LC Collateral, and all proceeds thereof to secure its Matured LC
Obligations and its Obligations under this Agreement, each Note, and the other
Loan Documents, and Borrower agrees that such LC Collateral, investments and
proceeds shall be subject to all of the terms and conditions of the Security
Documents. Borrower further agrees that LC Issuer shall have all of the rights
and remedies of a secured party under the Uniform Commercial Code as adopted in
the State of Texas with respect to such security interest and that an Event of
Default under this Agreement shall constitute a default for purposes of such
security interest.

        (d)    Payment of LC Collateral.    When Borrower is required to provide
LC Collateral for any reason and fails to do so on the day when required, LC
Issuer may without notice to Borrower or any other Related Person provide such
LC Collateral (whether by application of proceeds of other Collateral, by
transfers from other accounts maintained with LC Issuer, or otherwise) using any
available funds of Borrower or any other Person also liable to make such
payments. Any such amounts which are required to be provided as LC Collateral
and which are not provided on the date required shall, for purposes of each
Security Document, be considered past due Obligations owing hereunder, and LC
Issuer is hereby authorized to exercise its respective rights under each
Security Document to obtain such amounts."

        § 2.6.    Reliance by Agent.    The third sentence of Section 9.2 of the
Original Agreement is hereby amended in its entirety to read as follows:

"As to any matters not expressly provided for by this Agreement, Agent shall not
be required to exercise any discretion or take any action, but shall be required
to act or to refrain from acting (and shall be fully protected in so acting or
refraining from acting) upon the instructions of the Tranche A Majority Lenders,
Tranche B Majority Lenders or Majority Lenders, as provided in this Agreement,
and such instructions shall be binding on all of Tranche A Lenders, Tranche B
Lenders or Lenders, respectively; provided, however, that Agent shall not be
required to take any action that exposes Agent to personal liability or that is
contrary to any Loan Document or applicable law or unless it shall first be
indemnified to its satisfaction by Lenders against any and all liability and
expense which may be incurred by it by reason of taking any such action."

        § 2.7.    Waivers and Amendments.    Section 10.1(b) of the Original
Agreement is hereby amended in its entirety to read as follows:

        "(b) No waiver or supplement to this Agreement or the other Loan
Documents shall be valid or effective against any party hereto unless the same
is in writing and signed by (i) if such party is Borrower, by Borrower, (ii) if
such party is Agent, by Agent, (iii) if such party is Issuing Bank, by Issuing
Bank, (iv) in any provision requiring the consent of Tranche A Majority Lenders,
if such party is a Tranche A Lender, by such Tranche A Lender or by Agent on
behalf of Tranche A Lenders with the written consent of Tranche A Majority
Lenders, (v) in any provision requiring the consent of Tranche B Majority
Lenders, if such party is a Tranche B Lender, by such Tranche B Lender or by
Agent on behalf of Tranche B Lenders with the written consent of Tranche B
Majority Lenders, and (vi) in any provision requiring the consent of Majority
Lenders, if such party is a Lender, by Majority Lenders or by Agent on behalf of
Lenders with the written consent of Majority Lenders (which consent has already
been given as to the termination of the Loan Documents as provided in
Section 10.8). Notwithstanding the foregoing or anything to the contrary herein,
no such amendment or waiver shall, unless signed by all Lenders or by Agent on
behalf of all Lenders with the prior consent of each individual Lender,
(1) waive any of the conditions specified in Article IV (provided that Agent may
in its discretion withdraw any request it has made under Section 4.2(f)),
(2) increase the Percentage Share, the Tranche A Percentage Share, the Tranche B
Percentage Share or Commitment of such Lender or subject such Lender to any
additional obligations, (3) reduce any fees hereunder, or the principal of, or
interest on, such Lender's Note, (4) postpone any date fixed for any payment of
any fees hereunder, or principal of, or interest on, such Lender's Note,
(5) amend the definition herein of "Majority Lenders" or otherwise change the
aggregate amount of Percentage Shares which is required for Agent, Lenders or
any of them to take any particular action under the Loan Documents, (6) release
Borrower from its obligation to pay such Lender's Note or any Guarantor from its
guaranty of such payment, or (7) release any Collateral except in accordance
with the express terms of any Loan Document. Notwithstanding the foregoing or
anything to the contrary herein, Agent shall not, (a) without the prior consent
of each individual Tranche A Lender, execute and deliver on behalf of such
Tranche A Lender any waiver or amendment which would amend the definition herein
of "Tranche A Majority Lenders" and (b) without the prior consent of each
individual Tranche B Lender, execute and deliver on behalf of such Tranche B
Lender any waiver or amendment which would amend the definition herein of
"Tranche B Majority Lenders."

        § 2.8.    Limitation on Sales of Property.    The following
clause (C) is hereby added to subsection (iii) of Section 6.2(d) of the Original
Agreement:

        "(C)   the Toca gas processing and liquid fractionation facility located
in Saint Bernard Parish Louisiana; and"

        § 2.9.    Assignments and Participations.    Section 10.5 of the
Original Agreement is hereby amended in its entirety to read as follows:

        "(a) The provisions of this Agreement shall be binding upon and inure to
the benefit of the parties hereto and their respective successors and assigns
permitted hereby, except that the Borrower may not assign or otherwise transfer
any of its rights or obligations hereunder without the prior written consent of
each Lender (and any attempted assignment or transfer by the Borrower without
such consent shall be null and void). Nothing in this Agreement, expressed or
implied, shall be construed to confer upon any Person (other than the parties
hereto, their respective successors and assigns permitted hereby and, to the
extent expressly contemplated hereby, any indemnified party) any legal or
equitable right, remedy or claim under or by reason of this Agreement.

        (b)  Any Lender may assign to one or more Eligible Assignees all or a
portion of its rights and obligations under this Agreement (including all or a
portion of its Commitment and the Loans (including for purposes of this
subsection (b), participations in LC Obligations) at the time owing to it);
provided that (i) except in the case of an assignment of the entire remaining
amount of the assigning Lender's Commitment and the Loans at the time owing to
it or in the case of an assignment to a Lender or an Affiliate of a Lender or an
Approved Fund with respect to a Lender, the aggregate amount of the Commitment
(which for this purpose includes Loans outstanding thereunder) subject to each
such assignment, determined as of the date the Assignment and Acceptance with
respect to such assignment is delivered to the Agent, shall not be less than
$5,000,000, unless each of the Agent and, so long as no Event of Default has
occurred and is continuing, the Borrower otherwise consents (each such consent
not to be unreasonably withheld or delayed), (ii) each partial assignment shall
be made as an assignment of a proportionate part of all the assigning Lender's
rights and obligations under this Agreement with respect to the Loans or the
Commitment assigned, except that this clause (ii) shall not prohibit any Lender
from assigning all or a portion of its rights and obligations among separate
Tranches on a non-pro rata basis, and (iii) the parties to each assignment shall
execute and deliver to the Agent an Assignment and Acceptance, together with a
processing and recordation fee of $3,500. Subject to acceptance and recording
thereof by the Agent pursuant to subsection (c) of this Section, from and after
the effective date specified in each Assignment and Acceptance, the Eligible
Assignee thereunder shall be a party hereto and, to the extent of the interest
assigned by such Assignment and Acceptance, have the rights and obligations of a
Lender under this Agreement, and the assigning Lender thereunder shall, to the
extent of the interest assigned by such Assignment and Acceptance, be released
from its obligations under this Agreement (and, in the case of an Assignment and
Acceptance covering all of the assigning Lender's rights and obligations under
this Agreement, such Lender shall cease to be a party hereto but shall continue
to be entitled to the benefits of Section 9.11). The Borrower (at its expense)
shall execute and deliver new or replacement Notes to the assigning Lender and
the assignee Lender. Any assignment or transfer by a Lender of rights or
obligations under this Agreement that does not comply with this subsection shall
be treated for purposes of this Agreement as a sale by such Lender of a
participation in such rights and obligations in accordance with
subsection (d) of this Section.

        (c)  The Agent, acting solely for this purpose as an agent of the
Borrower, shall maintain at the Agent's office (which must be in the United
States of America) a copy of each Assignment and Acceptance delivered to it and
a register for the recordation of the names and addresses of the Lenders, and
the Commitments of, and principal amount of the Loans and LC Obligations owing
to, each Lender pursuant to the terms hereof from time to time (the "Register").
The entries in the Register shall be conclusive, and the Borrower, the Agent and
the Lenders may treat each Person whose name is recorded in the Register
pursuant to the terms hereof as a Lender hereunder for all purposes of this
Agreement, notwithstanding notice to the contrary. The Register shall be
available for inspection by the Borrower and any Lender, at any reasonable time
and from time to time upon reasonable prior notice.

        (d)  Any Lender may, without the consent of, or notice to, the Borrower
or theAgent, sell participations to one or more banks or other entities (a
"Participant") in all or a portion of such Lender's rights and/or obligations
under this Agreement (including all or a portion of its Commitment and/or the
Loans (including such Lender's participations in LC Obligations) owing to it);
provided that (i) such Lender's obligations under this Agreement shall remain
unchanged, (ii) such Lender shall remain solely responsible to the other parties
hereto for the performance of such obligations and (iii) the Borrower, the Agent
and the other Lenders shall continue to deal solely and directly with such
Lender in connection with such Lender's rights and obligations under this
Agreement. Any agreement or instrument pursuant to which a Lender sells such a
participation shall provide that such Lender shall retain the sole right to
enforce this Agreement and to approve any amendment, modification or waiver of
any provision of this Agreement; provided that such agreement or instrument may
provide that such Lender will not, without the consent of the Participant, agree
to any amendment, waiver or other modification that would (i) postpone any date
upon which any payment of money is scheduled to be paid to such Participant,
(ii) reduce the principal, interest, fees or other amounts payable to such
Participant,or (iii) release any Guarantor from its guaranty. Subject to
subsection (e) of this Section, the Borrower agrees that each Participant shall
be entitled to the benefits of Sections 2.10, 2.15, and 2.16 to the same extent
as if it were a Lender and had acquired its interest by assignment pursuant to
subsection (b) of this Section. To the extent permitted by law, each Participant
also shall be entitled to the benefits of Section 7.2 as though it were a
Lender.

        (e)  A Participant shall not be entitled to receive any greater payment
under Section 2.10 or 2.15 than the applicable Lender would have been entitled
to receive with respect to the participation sold to such Participant, unless
the sale of the participation to such Participant is made with the Borrower's
prior written consent. A Participant that would be a Foreign Lender if it were a
Lender shall not be entitled to the benefits of Section 2.15 unless the Borrower
is notified of the participation sold to such Participant and such Participant
agrees, for the benefit of the Borrower, to comply with Section 10.14 as though
it were a Lender.

        (f)    Any Lender may at any time pledge or assign a security interest
in all or any portion of its rights under this Agreement (including under its
Notes, if any) to secure obligations of such Lender, including any pledge or
assignment to secure obligations to a Federal Reserve Bank; provided that no
such pledge or assignment shall release a Lender from any of its obligations
hereunder or substitute any such pledgee or assignee for such Lender as a party
hereto.

        (g)  If the consent of the Borrower to an assignment or to an Eligible
Assignee is required hereunder (including a consent to an assignment which does
not meet the minimum assignment threshold specified in clause (i) of the proviso
to the first sentence of Section 10.5(b)), the Borrower shall be deemed to have
given its consent five Business Days after the date notice thereof has been
delivered by the assigning Lender (through the Agent) unless such consent is
expressly refused by the Borrower prior to such fifth Business Day.

        (h)  As used herein, the following terms have the following meanings:

        "Fund" means any Person (other than a natural Person) that is (or will
be) engaged in making, purchasing, holding or otherwise investing in commercial
loans and similar extensions of credit in the ordinary course of its business.

        "Approved Fund" means any Fund that is administered or managed by (a) a
Lender, (b) an Affiliate of a Lender or (c) an entity or an Affiliate of an
entity that administers or manages a Lender.

        (i)    Notwithstanding anything to the contrary contained herein, if at
any time Bank of America assigns its entire Percentage Share of the Commitment
and Loans pursuant to subsection (b) above, Bank of America may, (i) upon
30 days' notice to the Borrower and the Lenders, resign as LC Issuer. In the
event of any such resignation as LC Issuer, the Borrower shall be entitled to
appoint from among the Lenders a successor LC Issuer hereunder; provided,
however, that no failure by the Borrower to appoint any such successor shall
affect the resignation of Bank of America as LC Issuer. Bank of America shall
retain all the rights and obligations of the LC Issuer hereunder with respect to
all LC's outstanding as of the effective date of its resignation as LC Issuer
and all LC Obligations with respect thereto."

        § 2.10.    Foreign Lenders.    Section 10.14 is hereby added to the
Original Agreement to read as follows:

        "Section 10.14. Each Lender that is a "foreign corporation, partnership
or trust" within the meaning of the Internal Revenue Code of 1986 (a "Foreign
Lender") shall deliver to the Agent, prior to receipt of any payment subject to
withholding under the Internal Revenue Code of 1986 (or after accepting an
assignment of an interest herein), two duly signed completed copies of either
IRS Form W-8BEN or any successor thereto (relating to such Person and entitling
it to an exemption from, or reduction of, withholding tax on all payments to be
made to such Person by the Borrower pursuant to this Agreement) or IRS
Form W-8ECI or any successor thereto (relating to all payments to be made to
such Person by the Borrower pursuant to this Agreement) or such other evidence
satisfactory to the Borrower and the Agent that such Person is entitled to an
exemption from, or reduction of, U.S. withholding tax. Thereafter and from time
to time, each such Person shall (a) promptly submit to the Agent such additional
duly completed and signed copies of one of such forms (or such successor forms
as shall be adopted from time to time by the relevant United States taxing
authorities) as may then be available under then current United States laws and
regulations to avoid, or such evidence as is satisfactory to the Borrower and
the Agent of any available exemption from or reduction of, United States
withholding taxes in respect of all payments to be made to such Person by the
Borrower pursuant to this Agreement, (b) promptly notify the Agent of any change
in circumstances which would modify or render invalid any claimed exemption or
reduction, and (c) take such steps as shall not be materially disadvantageous to
it, in the reasonable judgment of such Lender, and as may be reasonably
necessary (including the re-designation of its Lending Office) to avoid any
requirement of applicable Laws that the Borrower make any deduction or
withholding for taxes from amounts payable to such Person. If such Person fails
to deliver the above forms or other documentation, then the Agent may withhold
from any interest payment to such Person an amount equivalent to the applicable
withholding tax imposed by Sections 1441 and 1442 of the Internal Revenue Code
of 1986, without reduction. If any governmental authority asserts that the Agent
did not properly withhold any tax or other amount from payments made in respect
of such Person, such Person shall indemnify the Agent therefor, including all
penalties and interest, any taxes imposed by any jurisdiction on the amounts
payable to the Agent under this Section, and costs and expenses (including
Attorney Costs) of the Agent. The obligation of the Lenders under this
Section shall survive the payment of all Obligations and the resignation or
replacement of the Agent."

        § 2.11.    Lenders Schedule and Assignment and Acceptance.    Schedule 3
attached to the Original Agreement is deleted and Schedule 3 hereto is
substituted therefor. Exhibit G attached to the Original Agreement is deleted
and Exhibit G hereto is substituted therefor.

ARTICLE IIA.
Amendment to Intercreditor Agreement

        § 2.1A.    Amendment to Intercreditor Agreement.    Each of Agent,
Prudential, as successor in interest to PICA and each Lender hereby agrees that
the term "Prudential Affiliate" in the Original Intercreditor Agreement is
hereby amended in its entirety to mean the following:

"Prudential Affiliate" shall mean any corporation or other entity controlling,
controlled by, or under common control with, Prudential Investment
Management, Inc. ("Prudential") either directly or through subsidiaries and
(ii) any managed account or investment fund which is managed by Prudential or a
Prudential Affiliate described in clause (i) of this definition.

Agent, Prudential and Lenders hereby further agree that, for purposes of the
definition of "Prudential Affiliate" the terms "control", "controlling" and
"controlled" shall mean the ownership, directly or through subsidiaries, of a
majority of a corporation's or other entity's voting stock or equivalent voting
securities or interests.

ARTICLE IIB.
Consent to Restated Master Shelf Agreement

        § 2.1B.    Consent of Majority Lenders.    Majority Lenders hereby
consent to Borrower's execution of the Restated Prudential Agreement and the
provisions contained therein, including without limitation, the extension of the
period during which senior notes may be issued thereunder and the increase of
the facility size by $65,000,000 (allowing Borrower to issue an additional
$65,000,000 in Debt Securities).

ARTICLE III.
Conditions of Effectiveness

        § 3.1.    Effective Date.    

        (a)  Article II of this Amendment shall become effective as of July 30,
2002 when, and only when:

        (i)    Agent shall have received this Amendment, duly authorized,
executed and delivered by Borrower, Agent, and Lenders in form and substance
satisfactory to Agent;

        (ii)  Agent shall have received a certificate of a duly authorized
officer of Borrower dated the date of this Amendment certifying: (i) that all of
the representations and warranties set forth in Article IV hereof are true and
correct at and as of the time of such effectiveness; and(ii) as to such other
corporate matters as Agent shall deem necessary;

        (iii)  Agent shall have received an opinion of General Counsel to
Borrower with respect to this Amendment, in form and substance acceptable to
Agent;

        (iv)  All fees and disbursements of Thompson & Knight L.L.P. relating to
this Amendment and the Loan Agreement as provided in the Loan Agreement have
been fully paid; and

        (v)  Agent shall have additionally received such other documents as
Agent may reasonably request.

        (b)  Article IIA of this Amendment shall become effective as of the date
first written above when and only when Agent shall have received this Amendment,
duly authorized, executed and delivered by Agent, each Lender and Prudential.

        (c)  The remainder of this Amendment shall become effective as of the
date first written above when and only when:

        (i)    Agent shall have received this Amendment, duly authorized,
executed and delivered by Borrower, Agent, and Majority Lenders in form and
substance satisfactory to Agent; and

        (ii)  All of the conditions listed in subsections (a)(ii) through
(a)(v) of this Section 3.1 have been satisfied.

ARTICLE IV.
Representations and Warranties

        § 4.1.    Representations and Warranties of Borrower.    In order to
induce each Lender to enter into this Amendment, Borrower represents and
warrants on the date hereof and as of the Effective Date to each Lender that:

        (a)  The representations and warranties contained in Article V of the
Original Agreement are true and correct at and as of the time of the
effectiveness hereof (except as such representations and warranties have been
modified by the transactions contemplated herein).

        (b)  Borrower is duly authorized to execute and deliver this Amendment
and Borrower is and will continue to be duly authorized to borrow monies and to
perform its obligations under the Loan Agreement. Borrower has duly taken all
corporate action necessary to authorize the execution and delivery of this
Amendment.

        (c)  The execution and delivery by Borrower of this Amendment, the
performance of its obligations hereunder and the consummation of the
transactions contemplated hereby do not and will not conflict with any provision
of law, statute, rule or regulation or of the certificate of incorporation and
bylaws of Borrower or of any material agreement, judgment, license, order or
permit applicable to or binding upon Borrower or result in the creation of any
lien, charge or encumbrance upon any assets or properties of Borrower. Except
for those which have been obtained, no consent, approval, authorization or order
of any court or governmental authority or third party is required in connection
with the execution and delivery by Borrower of this Amendment.

        (d)  When duly executed and delivered, this Amendment, the Loan
Agreement, and each other Loan Document, as affected hereby, will be a legal and
binding obligation of each Related Person that is a party hereto and thereto
enforceable against such Related Person in accordance with its terms, except as
limited by bankruptcy, insolvency or similar laws of general application
relating to the enforcement of creditors' rights and by equitable principles of
general application.

        (e)  The audited Consolidated financial statements of Borrower dated as
of December 31, 2001, and the unaudited Consolidated financial statements of
Borrower dated as of September 30, 2002, fairly present the Consolidated
financial position at such date of Borrower and the Consolidated statement of
operations and the changes in Consolidated financial position for the periods
ending on such date for Borrower. Copies of such financial statements have
heretofore been delivered to Agent. Since December 31, 2001, no material adverse
change has occurred in the financial condition or business or in the
Consolidated financial condition or business of Borrower.

ARTICLE V.
Miscellaneous

        § 5.1.    Ratification of Agreements.    The Original Agreement as
hereby amended is hereby ratified and confirmed in all respects. Any reference
to the Loan Agreement in any Loan Document shall be deemed to be a reference to
the Original Agreement as hereby amended. The Loan Documents, as they may be
amended or affected by this Amendment, are hereby ratified and confirmed in all
respects. The execution, delivery and effectiveness of this Amendment shall not,
except as expressly provided herein, operate as a waiver of any right, power or
remedy of Lenders under the Loan Agreement, the Notes, or any other Loan
Document nor constitute a waiver of any provision of the Loan Agreement, the
Notes, or any other Loan Document.

        § 5.2.    Survival of Agreements.    All representations, warranties,
covenants and agreements of Borrower herein shall survive the execution and
delivery of this Amendment and the performance hereof, including without
limitation the making or granting of the Loans, and shall further survive until
all of the Obligations are paid in full. All statements and agreements contained
in any certificate or instrument delivered by Borrower hereunder or under the
Loan Agreement to any Lender shall be deemed to constitute representations and
warranties by, and/or agreements and covenants of, Borrower under this Amendment
and under the Loan Agreement.

        § 5.3.    Loan Documents.    This Amendment is a Loan Document, and all
provisions in the Loan Agreement pertaining to Loan Documents apply hereto.

        § 5.4.    Governing Law.    This Amendment shall be governed by and
construed in accordance the laws of the State of Texas and any applicable laws
of the United States of America in all respects, including construction,
validity and performance.

        § 5.5.    Counterparts.    This Amendment may be separately executed in
counterparts and by the different parties hereto in separate counterparts, each
of which when so executed shall be deemed to constitute one and the same
Amendment. This Amendment may be duly executed by facsimile or other electronic
transmission.

        THIS AMENDMENT AND THE OTHER LOAN DOCUMENTS 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 ORAL AGREEMENTS OF THE PARTIES.

[THE REMAINDER OF THIS PAGE IS INTENTIONALLY LEFT BLANK.]

        IN WITNESS WHEREOF, this Amendment is executed as of the date first
above written.

 
 
WESTERN GAS RESOURCES, INC.
 
 
By:
 

--------------------------------------------------------------------------------

Name:
Title:
 
 
BANK OF AMERICA, N.A., as Agent and Lender
 
 
By:
 

--------------------------------------------------------------------------------

Name:
Title:
 
 
ABN AMRO BANK N.V., a Lender
 
 
By:
 

--------------------------------------------------------------------------------

Name:
Title:
 
 
By:
 

--------------------------------------------------------------------------------

Name:
Title:
 
 
BANK ONE, NA (MAIN OFFICE—CHICAGO), a Lender
 
 
By:
 

--------------------------------------------------------------------------------

Name:
Title:
 
 
COMERICA BANK—TEXAS, a Lender
 
 
By:
 

--------------------------------------------------------------------------------

Name:
Title:
 
 
CREDIT LYONNAIS NEW YORK BRANCH, a Lender
 
 
By:
 

--------------------------------------------------------------------------------

Name:
Title:

 
 
FLEET NATIONAL BANK, a Lender
 
 
By:
 

--------------------------------------------------------------------------------

Name:
Title:
 
 
SOCIÉTÉ GÉNÉRALE SOUTHWEST AGENCY, a Lender
 
 
By:
 

--------------------------------------------------------------------------------

Name:
Title:
 
 
UNION BANK OF CALIFORNIA, N.A., a Lender
 
 
By:
 

--------------------------------------------------------------------------------

Name:
Title:
 
 
U.S. BANK NATIONAL ASSOCIATION, a Lender
 
 
By:
 

--------------------------------------------------------------------------------

Name:
Title:
 
 
WELLS FARGO BANK, N.A., a Lender
 
 
By:
 

--------------------------------------------------------------------------------

Name:
Title:

        The undersigned is executing this Tenth Amendment to Loan Agreement and
Amendment to Intercreditor Agreement for the sole purpose of agreeing to
Section 2.1A, Amendment to Intercreditor Agreement, and for no other purpose.

 
 
PRUDENTIAL INVESTMENT MANAGEMENT, INC., for itself and on behalf of the holders
of the Notes
 
 
By:
 

--------------------------------------------------------------------------------

Name:
Title:

CONSENT AND AGREEMENT

        Each of the undersigned hereby (i) consents to the provisions of this
Amendment and the transactions contemplated herein, and (ii) ratifies and
confirms its respective Guaranty dated as of April 29, 1999 made by it in favor
of Agent for the benefit of each Lender, and agrees that its obligations and
covenants thereunder are unimpaired hereby and shall remain in full force and
effect. This Consent and Agreement is effective as of July 30, 2002.

Date:                        , 2003

 
 
MIGC, INC.
 
 
WESTERN GAS RESOURCES TEXAS, INC.
 
 
MOUNTAIN GAS RESOURCES, INC.
 
 
LANCE OIL & GAS COMPANY, INC.
 
 
WESTERN GAS WYOMING, L.L.C.
 
 
By:
 

--------------------------------------------------------------------------------

Name:
Title:

CONSENT AND AGREEMENT

        The undersigned hereby (i) consents to the provisions of this Amendment
and the transactions contemplated herein, and (ii) ratifies and confirms its
Guaranty dated as of October 14, 1999 made by it in favor of Agent for the
benefit of each Lender, and agrees that its obligations and covenants thereunder
are unimpaired hereby and shall remain in full force and effect. This Consent
and Agreement is effective as of July 30, 2002.

Date:                        , 2003

 
 
MGTC, INC.
 
 
By:
 

--------------------------------------------------------------------------------

Name:
Title:

EXHIBIT G

FORM OF ASSIGNMENT AND ACCEPTANCE

        Reference is made to that certain Loan Agreement, dated as of April 29,
1999 (as amended, restated, extended, supplemented or otherwise modified in
writing from time to time, the "Agreement;" the terms defined therein being used
herein as therein defined), among Western Gas Resources, Inc., a Delaware
corporation (the ''Borrower"), the Lenders from time to time party thereto, and
Bank of America, N.A., as Agent and Issuing Bank.

        The assignor identified on the signature page hereto (the "Assignor")
and the assignee identified on the signature page hereto (the "Assignee") agree
as follows:

        1.    (a) Subject to paragraph 11, effective as of the date specified on
Schedule 1 hereto (the "Effective Date"), the Assignor hereby irrevocably sells
and assigns to the Assignee without recourse to the Assignor, and the Assignee
hereby irrevocably purchases and assumes from the Assignor without recourse to
the Assignor, the interest described on Schedule 1 hereto (the "Assigned
Interest") in and to the Assignor's rights and obligations under the Agreement.

        (b)  From and after the Effective Date, (i) the Assignee shall be a
party under the Agreement and will have all the rights and obligations of a
Lender for all purposes under the Loan Documents to the extent of the Assigned
Interest and be bound by the provisions thereof, and (ii) the Assignor shall
relinquish its rights and be released from its obligations under the Agreement
to the extent of the Assigned Interest. The Assignor and/or the Assignee, as
agreed by the Assignor and the Assignee, shall deliver, in immediately available
funds, any applicable assignment fee required under Section 10.5 of the
Agreement.

        2.    On the Effective Date, the Assignee shall pay to the Assignor, in
immediately available funds, an amount equal to the purchase price of the
Assigned Interest as agreed upon by the Assignor and the Assignee.

        3.    From and after the Effective Date, the Agent shall make all
payments under the Agreement and the Notes, if any, in respect of the Assigned
Interest (including all payments of principal, interest and fees with respect
thereto) to the Assignee. The Assignor and the Assignee shall make all
appropriate adjustments in payments under the Agreement and such Notes, if any,
for periods prior to the Effective Date directly between themselves.

        4.    The Assignor represents and warrants to the Assignee that:

        (a)  The Assignor is the legal and beneficial owner of the Assigned
Interest, and the Assigned Interest is free and clear of any adverse claim;

        (b)  the Assigned Interest listed on Schedule 1 accurately and
completely sets forth the outstanding amount of all Loans and LC Obligations
relating to the Assigned Interest as of the Effective Date;

        (c)  it has the power and authority and the legal right to make, deliver
and perform, and has taken all necessary action, to authorize the execution,
delivery and performance of this Assignment and Acceptance, and any and all
other documents delivered by it in connection herewith and to fulfill its
obligations under, and to consummate the transactions contemplated by, this
Assignment and Acceptance and the Loan Documents, and no consent or
authorization of, filing with, or other act by or in respect of any governmental
authority, is required in connection in connection herewith or therewith; and

        (d)  this Assignment and Acceptance constitutes the legal, valid and
binding obligation of the Assignor.

        The Assignor makes no representation or warranty and assumes no
responsibility with respect to the financial condition of the Borrower or any of
its Affiliates or the performance by the Borrower or any of its Affiliates of
their respective obligations under the Loan Documents, and assumes no
responsibility with respect to any statements, warranties or representations
made under or in connection with any Loan Document or the execution, legality,
validity, enforceability, genuineness, sufficiency or value of any Loan Document
other than as expressly set forth above.

        5.    The Assignee represents and warrants to the Assignor and the Agent
that:

        (a)  it is an Eligible Assignee;

        (b)  it has the full power and authority and the legal right to make,
deliver and perform, and has taken all necessary action, to authorize the
execution, delivery and performance of this Assignment and Acceptance, and any
and all other documents delivered by it in connection herewith and to fulfill
its obligations under, and to consummate the transactions contemplated by, this
Assignment and Acceptance and the Loan Documents, and no consent or
authorization of, filing with, or other act by or in respect of any governmental
authority, is required in connection in connection herewith or therewith;

        (c)  this Assignment and Acceptance constitutes the legal, valid and
binding obligation of the Assignee;

        (d)  under applicable laws no tax will be required to be withheld by the
Agent or the Borrower with respect to any payments to be made to the Assignee
hereunder or under any Loan Document, and unless otherwise indicated in the
space opposite the Assignee's signature below, no tax forms described in
Section 2.14(d) of the Agreement are required to be delivered by the Assignee;
and

        (e)  the Assignee has received a copy of the Agreement, together with
copies of the most recent financial statements of the Borrower delivered
pursuant thereto, and such other documents and information as it has deemed
appropriate to make its own credit analysis and decision to enter into this
Assignment and Acceptance. The Assignee has independently and without reliance
upon the Assignor or the Agent and based on such information as the Assignee has
deemed appropriate, made its own credit analysis and decision to enter into this
Assignment and Acceptance. The Assignee will, independently and without reliance
upon the Agent or any Lender, and based upon such documents and information as
it shall deem appropriate at the time, continue to make its own credit decisions
in taking or not taking action under the Agreement.

        6.    The Assignee appoints and authorizes the Agent to take such action
as agent on its behalf and to exercise such powers and discretion under the
Agreement, the other Loan Documents or any other instrument or document
furnished pursuant hereto or thereto as are delegated to the Agent by the terms
thereof, together with such powers as are incidental thereto.

        7.    If either the Assignee or the Assignor desires a Note to evidence
its Loans, it shall request the Agent to procure a Note from the Borrower.

        8.    The Assignor and the Assignee agree to execute and deliver such
other instruments, and take such other action, as either party may reasonably
request in connection with the transactions contemplated by this Assignment and
Acceptance.

        9.    This Assignment and Acceptance shall be binding upon and inure to
the benefit of the parties and their respective successors and assigns;
provided, however, that the Assignee shall not assign its rights or obligations
hereunder without the prior written consent of the Assignor and any purported
assignment, absent such consent, shall be void.

        10.  This Assignment and Acceptance may be executed by facsimile
signatures with the same force and effect as if manually signed and may be
executed in one or more counterparts, each of which shall be deemed an original,
but all of which together shall constitute one and the same instrument. This
Assignment and Acceptance shall be governed by and construed in accordance with
the laws of the state specified in the Section of the Agreement entitled
"Governing Law."

        11.  The effectiveness of the assignment described herein is subject to:

        (a)  if such consent is required by the Agreement, receipt by the
Assignor and the Assignee of the consent of the Agent, the Issuing Bank and/or
the Borrower to the assignment described herein. By delivering a duly executed
and delivered copy of this Assignment and Acceptance to the Agent, the Assignor
and the Assignee hereby request any such required consent and request that the
Agent register the Assignee as a Lender under the Agreement effective as of the
Effective Date; and

        (b)  receipt by the Agent of (or other arrangements acceptable to the
Agent with respect to) any applicable assignment fee referred to in Section 10.5
of the Agreement and any tax forms required by Section 2.14(d) of the Agreement.

        By signing below, the Agent agrees to register the Assignee as a Lender
under the Agreement, effective as of the Effective Date with respect to the
Assigned Interest, and will adjust the registered Percentage Share of the
Assignor under the Agreement to reflect the assignment of the Assigned Interest.

        12.  Attached hereto as Schedule 2 is all contact, address, account and
other administrative information relating to the Assignee.

        IN WITNESS WHEREOF, the parties hereto have caused this Assignment and
Acceptance to be executed as of the date first above written by their respective
duly authorized officers.

 
 
Assignor:
 
 
[Name of Assignor]
 
 
By:
 

--------------------------------------------------------------------------------

    Name:  

--------------------------------------------------------------------------------

    Title:  

--------------------------------------------------------------------------------

Tax forms required by Section 2.14(d) of the Agreement included
 
Assignee:
[Name of Assignee]
 
 
By:
 

--------------------------------------------------------------------------------

    Name:  

--------------------------------------------------------------------------------

    Title:  

--------------------------------------------------------------------------------

(Signatures continue)        

In accordance with and subject to Section 10.05 of the Loan Agreement, the
undersigned consent to the foregoing assignment as of the Effective Date:

WESTERN GAS RESOURCES, INC.
 
 
By:
 

--------------------------------------------------------------------------------

 
  Name:  

--------------------------------------------------------------------------------

    Title:  

--------------------------------------------------------------------------------

   
BANK OF AMERICA, N.A., as Agent and LC Issuer
 
 
By:
 

--------------------------------------------------------------------------------

 
  Name:  

--------------------------------------------------------------------------------

    Title:  

--------------------------------------------------------------------------------

   

SCHEDULE 1
TO
ASSIGNMENT AND ACCEPTANCE

THE ASSIGNED INTEREST

Effective Date:

Assigned Commitment

--------------------------------------------------------------------------------

  Type and amount of outstanding Obligations assigned

--------------------------------------------------------------------------------

  Assigned Tranche A Percentage Share/Tranche B Percentage Share

--------------------------------------------------------------------------------

$                      [type]$                     %

SCHEDULE 2
TO
ASSIGNMENT AND ACCEPTANCE

ADMINISTRATIVE DETAILS

        (Assignee to list names of credit contacts, addresses, phone and
facsimile numbers, electronic mail addresses and account and payment
information)

QuickLinks

Exhibit 10.28