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                                                                    EXHIBIT 4.1
                              AMENDED AND RESTATED
                          REGISTRATION RIGHTS AGREEMENT

         THIS AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT (this
"AGREEMENT") is made and entered into as of the 8th day of February, 2000, by
and among Vista Energy Resources, Inc., a Delaware corporation (the "COMPANY"),
Prize Energy Corp., a Delaware corporation ("PRIZE"), and each of the parties
listed as Owners on Exhibit A hereto (collectively, the "OWNERS" and,
individually, an "OWNER"). Certain terms used herein are defined in Section 3 of
this Agreement.

         1. Background. The Company, Prize and PEC Acquisition Corp., a Delaware
corporation ("MERGER SUB"), have entered into a transaction, which was
consummated on the date hereof, in which Merger Sub was merged with and into
Prize, Prize became a wholly-owned subsidiary of the Company and the
stockholders of Prize received shares of capital stock in the Company in
exchange for their shares of capital stock in Prize (the "MERGER"). The Company
and the Vista Holders are parties to a Registration Rights Agreement dated
October 28, 1998 (the "PRIOR VISTA AGREEMENT"). Prize and the Prize Holders are
parties to an Amended and Restated Registration Rights Agreement dated June 29,
1999 (the "PRIOR PRIZE AGREEMENT"). The parties hereto desire to enter into this
Agreement in order to terminate and replace the Prior Vista Agreement and the
Prior Prize Agreement and to set forth the rights of the parties hereto with
respect to the registration of the shares of capital stock of the Company. The
Prior Vista Agreement and the Prior Prize Agreement are hereby terminated and
canceled, effective on the date hereof, and shall have no further force or
effect.

         2. Registration under Securities Act, etc.

         2.1. Registration on Request.

         (a) Registration of Immediate Offering. Concurrently with or from time
to time after the Secondary Offering Date, subject to the limitations of Section
2.1(g) hereof, upon the written request (a "DEMAND REQUEST") of one or more
Owners, requesting that the Company effect the registration under the Securities
Act of all or a portion of such Owners' Registrable Securities (an "IMMEDIATE
OFFERING REGISTRATION") and specifying the number of Registrable Securities
requested to be registered and the intended method of disposition thereof
(including whether or not such requested disposition is to be in an underwritten
offering):

                  (i) Within five business days after the receipt of such
         request, the Company shall give written notice of the Demand Request
         (together with a copy of the Demand Request) to all other Owners of
         Registrable Securities, if any; and

                  (ii) After giving such notice and subject to the limitations
         set forth in Section 2.1(g) below, the Company shall use reasonable
         efforts to file a registration

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         statement with the Commission with respect to the Immediate Offering
         Registration as soon as is practicable but in any event no later than
         60 days after the Company's receipt of the Demand Request in order to
         effect the registration under the Securities Act of:

                           (A) the Registrable Securities which the Company is
                  requested to register in the Demand Request, and

                           (B) all other Registrable Securities which the
                  Company is requested to register by the Owners who give
                  written notice to the Company within 15 business days after
                  written notice of the Demand Request from the Company.

         The Owner's notice shall state the number of Registrable Securities
         requested to be registered and whether the request to register such
         securities constitutes a Demand Request pursuant to Section 2.1 of this
         Agreement or a request for Piggyback Registration (as defined in
         Section 2.2(a) hereof) pursuant to Section 2.2 of this Agreement. If
         such request constitutes a Demand Request, such written notice to the
         Company shall specify the intended method of disposition of the Owner's
         Registrable Securities (including whether or not such requested
         disposition is to be in an underwritten offering).

         (b) Registration of Delayed or Continuous Offering. Concurrently with
or from time to time after the Secondary Offering Date (or at any time, in the
case of a Shelf Registration, as defined below, which does not provide for
underwritten take-downs), subject to the limitations of Section 2.1(g) hereof,
upon the written request (the "SHELF REQUEST") of Pioneer, the Individual Vista
Holders or the Owners of more than 50% of the Registrable Securities held by
Owners other than Pioneer and the Individual Vista Holders, requesting that the
Company effect the registration under the Securities Act of all or a portion of
such Owners' Registrable Securities for resale in a delayed or continuous
offering to the extent permitted by Rule 415 (or any successor rule thereto)
under the Securities Act (a "SHELF REGISTRATION" and, together with an Immediate
Offering Registration, a "DEMAND OFFERING") and specifying the number of
Registrable Securities requested to be registered and the intended methods of
disposition thereof (including whether or not such requested registration is to
include underwritten offerings):

                  (i) Within five business days after the receipt of the Shelf
         Request, the Company shall give written notice of the Shelf Request
         (together with a copy of the Shelf Request) to all other Owners of
         Registrable Securities, if any; and

                  (ii) After giving such notice and subject to the limitations
         set forth in Section 2.1(g) below, the Company shall use reasonable
         efforts to file a registration statement with the Commission with
         respect to the Shelf Registration as soon as is reasonable but in any
         event no later than 60 days after the Company's receipt of the Shelf
         Request in order to effect the registration under the Securities Act
         of:

                           (A) the Registrable Securities which the Company is
                  requested to register in the Shelf Request, and

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                           (B) all other Registrable Securities which the
                  Company is requested to register by Owners who give written
                  notice to the Company within 15 business days after written
                  notice of the Shelf Request from the Company.

         The Owner's notice shall state the number of Registrable Securities
         requested to be registered, will constitute a Shelf Request hereunder,
         and shall specify the intended methods of disposition of the Owner's
         Registrable Securities (including whether or not such requested
         registration should include underwritten offerings).

         (c) Right to Defer Registration. Notwithstanding anything to the
contrary set forth in Sections 2.1(a) and 2.1(b) above, the Company shall not be
obligated to take any action to notify holders or to effect any Immediate
Offering Registration or Shelf Registration pursuant to Section 2.1(a) or 2.1(b)
above if the Company shall have furnished to the Owners requesting registration
a certificate signed by the Chairman or President and the Chief Financial
Officer of the Company stating that, in the good faith judgment of the Board of
Directors (excluding Board members designated by the holders requesting such
registration) of the Company, such request could materially interfere with bona
fide financing, acquisition, or other material business plans of the Company or
would require disclosure of non-public information, the premature disclosure of
which could materially adversely affect the Company. Such certificate shall
contain a general statement of the reasons for such deferral and an estimate of
the anticipated period of deferral, and the Company shall promptly notify the
holders requesting such registration of the expiration or earlier termination of
such deferral. If the Company defers the registration requested under this
Section 2.1, the Company shall promptly (but not later than 90 days following
the occurrence of the event or circumstances permitting the deferral) notify the
holders of Registrable Securities requesting such registration when the events
or circumstances permitting such deferral have ended and at that time shall
proceed with the requested registration and in accordance with this Agreement.
If the Company shall defer the requested registration pursuant to this Section
2.1(c), then any related requested registration may be withdrawn by the holder
of Registrable Securities requesting such registration by giving notice to the
Company at any time within 10 business days after the date the Company notifies
such holder of its willingness to proceed with the requested registration. Upon
such withdrawal, the withdrawn requested registration shall not count as an
exercise of the demand registration rights granted herein. Holders of
Registrable Securities shall not be liable to the Company for any filing or
other expenses incurred as a result of a withdrawal of a requested registration
made pursuant to this Section 2.1(c). The Company shall not defer a requested
registration more than one time in any continuous 12-month period.

         (d) Registration of Other Securities. Whenever the Company shall effect
a registration pursuant to this Section 2.1 in connection with an underwritten
offering by one or more holders of Registrable Securities, no securities other
than Registrable Securities shall be included among the securities covered by
such registration unless (i) the managing underwriter of such offering shall
have advised each holder of Registrable Securities to be covered by such
registration in writing that the inclusion of such other securities would not
adversely affect such offering, or (ii) the Requisite Holders of Registrable
Securities to be covered by such registration shall have consented in writing to
the inclusion of such other securities, or (iii) the offering is the Initial
Secondary Offering (in

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which case the only securities included shall be securities to be sold by the
Company and Registrable Securities in accordance with the applicable priority
provisions set forth in this Agreement).

         (e) Registration Statement Form. Registrations under this Section 2.1
shall be on such appropriate registration form of the Commission (i) as shall be
selected by the Company and as shall be reasonably acceptable to the Requisite
Holders, and (ii) as shall permit the disposition of such Registrable Securities
in accordance with the intended method or methods of disposition specified in
the request for such registration. The Company agrees to include in any such
registration statement all information which holders of Registrable Securities
being registered shall reasonably request.

         (f) Expenses. The Company shall pay all Registration Expenses in
connection with any registration of Registrable Securities requested pursuant to
this Section 2.1 and all Persons on whose behalf securities of the Company are
included in such registration shall pay their own Selling Expenses, with joint
costs allocated on the basis of the respective amounts of the securities then
being registered on their behalf.

         (g) Limitations on Requested Registrations. The Company's obligation to
take or continue any action to effect a requested registration under this
Section 2.1 shall be subject to the following limitations:

                  (i) The number of registrations that the Company is required
         to effect:

                           (A) at the request of Pioneer, shall not exceed one
                  registration under Section 2.1(k) below and two Demand
                  Registrations, one of which may be a Shelf Registration,

                           (B) at the request of the Individual Vista Holders,
                  shall not exceed one Demand Registration, which may be a Shelf
                  Registration, but the Company shall not be required to effect
                  any Shelf Registration which provides for underwritten
                  take-downs until Pioneer shall no longer own any Registrable
                  Securities, and

                           (C) at the request of the holders of Registrable
                  Securities other than Pioneer, shall not exceed two Immediate
                  Offering Registrations and one Shelf Registration; provided,
                  however, that no more than one such registration request shall
                  be effected on Form S-1 and the remainder shall be effected on
                  Form S-3 (such references herein to Securities Act
                  registration forms shall be deemed to also refer to any
                  successor forms thereto);

         provided, that a registration requested pursuant to this Section 2.1
         shall not be deemed to have been effected (x) unless a registration
         statement with respect thereto has been declared effective and remained
         effective for a period of at least 90 days (or, with respect to a Shelf
         Registration, until the earlier of the date on which all securities
         covered thereby have ceased to be Registrable Securities or the date on
         which all of such securities have been disposed

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         of in accordance with the intended methods of disposition by the seller
         or sellers thereof, subject to the provisions of Section 2.1(l) below),
         (y) if, after a registration statement has become effective, such
         registration is interfered with by any stop order, injunction or other
         order or requirement of the Commission or other governmental agency or
         court for any reason, or (z) if the conditions to closing specified in
         the purchase agreement or underwriting agreement entered into in
         connection with such registration are not satisfied, other than as a
         result of the voluntary termination of such offering by the Requisite
         Holders;

                  (ii) Except for the rights of Pioneer to initiate registration
         under this Section 2.1 and the rights of the Individual Vista Holders
         to initiate registration under the circumstances set forth in Section
         2.1(g)(i)(B) above, the Company shall not be required to effect a
         Registration or an underwritten takedown off of a Shelf Registration
         pursuant to this Section 2.1 unless such registration has been
         initiated by the holders of Registrable Securities other than Pioneer
         which represent at least 30% of the Registrable Securities then
         outstanding, and have an estimated aggregate offering price to the
         public of at least $3,000,000;

                  (iii) The Company shall not be required to effect any
         registration pursuant to this Section 2.1 during the applicable waiting
         period (defined below) following the filing of a registration statement
         under the Securities Act with respect to the public offering of any
         class of the Company's equity securities in an Immediate Offering
         Registration or an underwritten take-down off a Shelf Registration,
         whether such offering is for the account of the Company or the account
         of the owners of its equity securities (other than a registration of
         securities with respect to an employee benefit, retirement or similar
         plan or pursuant to the Midland Agreement); for purposes of this clause
         (iii), the "APPLICABLE WAITING PERIOD" shall be a period commencing
         upon the filing of the registration statement for such Immediate
         Offering Registration or underwritten take-down and extending for a
         period of 90 days following the earlier of (A) the date of final
         disposition of all securities offered for sale pursuant to such
         registration statement in accordance with the intended methods of
         disposition by the seller or sellers thereof, or (B) the date of the
         termination or withdrawal of such registration statement; provided,
         that, if the Company shall have entered into an agreement in connection
         with any underwritten public offering of securities that restricts the
         registration or sale of the Company's equity securities (a "LOCK-UP
         AGREEMENT") for a period longer than 90 days, the applicable waiting
         period shall be the lesser of (x) the period specified in the Lock-Up
         Agreement, or (y) 180 days; and

                  (iv) The Company shall not be required to effect any
         registration pursuant to this Section 2.1 during the applicable waiting
         period (defined below) following the filing of a registration statement
         under the Securities Act with respect to the public offering of any
         class of the Company's equity securities in a Shelf Registration; for
         purposes of this clause (iv), the "APPLICABLE WAITING PERIOD" shall be
         a period (A) commencing upon the filing of the registration statement
         for such Shelf Registration and extending for a period of 90 days
         following the date on which such registration statement becomes
         effective, and (B) commencing upon an underwritten take-down from such
         Shelf Registration and extending for a period of 90 days thereafter.

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                  (h) Selection of Underwriters. If a Demand Offering pursuant
         to this Section 2.1 involves an underwritten offering, the underwriter
         or underwriters thereof shall be selected by the Requisite Holders with
         the approval of the Company.

                  (i) Priority in Requested Registrations.

                           (i) In the Initial Secondary Offering, including such
                  an offering pursuant to Section 2.1(k) hereof, Pioneer shall
                  have the right to include Registrable Securities in such
                  offering without being subject to any cutback, without
                  Pioneer's written consent, to the extent of the lesser of (A)
                  shares with a value (based on the final offering price to the
                  public) of $50,000,000, or (B) 50 percent of the total number
                  of shares to be sold in offering, plus 50 percent of any
                  over-allotment for such offering (the "PIONEER PRIORITY
                  AMOUNT") and no Prize Holder or Vista Holder (other than an
                  Individual Vista Holder) shall have any right to include
                  shares in the Initial Secondary Offering, without Pioneer's
                  written consent; provided that, if the Initial Secondary
                  Offering does not include any shares to be sold by the
                  Company, the limitation in clause (B) above shall not be
                  applicable and the Pioneer Priority Amount will only be
                  limited to an amount less than $50,000,000 if the managing
                  underwriter of such Demand Offering shall advise the Company
                  and Pioneer in writing that the amount of Registrable
                  Securities included in the Initial Secondary Offering must be
                  limited to a lesser amount (which shall be specified in the
                  notice) in order to prevent the Initial Secondary Offering
                  from materially and adversely affecting the price or success
                  of any subsequent offerings to be initiated by the Company
                  within the period of 180 days to 360 days following the
                  Initial Secondary Offering, in which case the Pioneer Priority
                  Amount shall be such lesser amount specified by such managing
                  underwriter.

                           (ii) In the first underwritten Demand Offering
                  following the Initial Secondary Offering (including, without
                  limitation, a take-down under a Shelf Registration), if the
                  managing underwriter of such Demand Offering shall advise the
                  Company in writing (with a copy to the Owners of Registrable
                  Securities that made the Demand Request with respect to such
                  Demand Offering) that the inclusion of the number of
                  securities requested to be included in such Demand Offering
                  will materially and adversely affect the price or success of
                  such Demand Offering, the Company will include in such
                  registration, to the extent of the number of securities which
                  the Company is so advised can be sold in such Demand Offering,
                  Registrable Securities requested to be included in such
                  registration allocated as follows (and any amounts above the
                  amounts so allocated shall not be included): Pioneer shall
                  have the right to sell 50 percent of the Registrable
                  Securities to be sold in such Demand Offering and the
                  remaining 50 percent of the Registrable Securities to be sold
                  in such Demand Offering shall be allocated pro rata among the
                  other Owners of Registrable Securities who elected to
                  participate in such Demand Offering pursuant to a Demand
                  Request given in accordance with Section 2.1(a)(ii)(B) hereof
                  ("OTHER DEMAND OWNERS") on the basis of the percentage of the
                  Registrable Securities of the Company held by each such Other
                  Demand Owner to the total Registrable Securities of all such
                  Other Demand Owners); provided, that, if there is any
                  over-allotment for such Demand Offering, the allocation of
                  Registrable Securities among Pioneer and each of the Other
                  Demand Owners that will satisfy such over-allotment shall be

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                  based on each selling Owner's percentage ownership of all of
                  the Registrable Securities then owned by all such selling
                  Owners.

                           (iii) In the second underwritten Demand Offering
                  following the Initial Secondary Offering and each underwritten
                  Demand Offering thereafter (including, without limitation,
                  take-downs under a Shelf Registration), if the managing
                  underwriter of such Demand Offering shall advise the Company
                  in writing (with a copy to the Owners of Registrable
                  Securities that made the Demand Request with respect to such
                  Demand Offering) that the inclusion of the number of
                  securities requested to be included in such Demand Offering
                  will materially and adversely affect the price or success of
                  such Demand Offering, the Company will include in such
                  registration, to the extent of the number of securities which
                  the Company is so advised can be sold in such Demand Offering,
                  Registrable Securities requested to be included in such
                  registration pro rata among the Owners thereof who submitted
                  such Demand Request (including, without limitation, all such
                  Owners who elect to participate in such Demand Offering
                  pursuant to a Demand Request given in accordance with Section
                  2.1(a)(ii)(B) hereof) on the basis of the percentage of the
                  Registrable Securities of the Company held by the Owners of
                  such Registrable Securities (and amounts above the amounts so
                  allocated shall not be included); provided, however, in the
                  event the number of Registrable Securities which the Owners of
                  Registrable Securities requested to be included in a Demand
                  Offering is reduced by more than 2%, those Owners of
                  Registrable Securities shall have the right to one additional
                  demand registration under Section 2.1(g) above.

                  (j) Holdback Period. If required by the underwriter or
         underwriters selected by the Company for an underwritten offering
         pursuant to this Section 2.1 (collectively, the "UNDERWRITER"), all
         Owners (whether or not they propose to distribute their Registrable
         Securities through such underwriting) shall agree not to sell publicly
         any of their Registrable Securities for such period as the Underwriter
         may reasonably request; provided, that such period shall not exceed 90
         continuous days.

                  (k) Initial Secondary Offering. Notwithstanding the other
         provisions of this Agreement, except as set forth in this Section
         2.1(k), the Company shall not effect a registration, other than a Shelf
         Registration which does not provide for underwritten take-downs, under
         this Section 2.1 if an Initial Secondary Offering has not occurred.
         After the date of this Agreement, Pioneer shall have the right to
         require the Company to effect an Initial Secondary Offering or to
         include Pioneer's Registrable Securities in an Initial Secondary
         Offering that the Company initiates, whereupon the Company shall be
         required to use reasonable efforts to effect such registration in
         accordance with this Section 2.1. Any shares included by any Owner
         (other than Pioneer) in an offering initiated by the Company or the
         offering initiated pursuant to this Section 2.1(k) will be deemed
         included pursuant to that Owner's rights under Section 2.2 hereof.

                  (l) Suspension of the Distribution of the Shares.

                           (i) In connection with any Shelf Registration, if the
                  Company determines in good faith that the distribution of any
                  of the Registrable Securities would materially interfere with

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                  bona fide financing, acquisition, or other material business
                  plans of the Company or any of its subsidiaries or would
                  require disclosure of non-public information, the premature
                  disclosure of which could materially adversely affect the
                  Company, and promptly gives the holders of Registrable
                  Securities included in such registration written notice of
                  such determination, the Company shall be entitled to require
                  said holders to suspend their distribution of the Registrable
                  Securities for a reasonable period of time which, for purposes
                  of this Section 2.1(l)(i), shall not exceed 90 days. Such
                  written notice shall contain a general statement of the
                  reasons for such suspension and an estimate of the anticipated
                  period of suspension, and the Company shall promptly notify
                  said holders of the expiration or earlier termination of such
                  suspension. If the Company shall suspend a Shelf Registration
                  pursuant to this Section 2.1(l)(i), then the Company shall
                  extend the effectiveness of the applicable registration
                  statement by the same number of days comprising the suspension
                  period. Alternatively, if the Company shall suspend a Shelf
                  Registration pursuant to this Section 2.1(l)(i) for more than
                  10 business days, then any related requested registration may
                  be withdrawn by the holder of Registrable Securities
                  requesting such registration by giving notice to the Company
                  at any time within 10 business days after the date the Company
                  notifies such holder of its willingness to proceed with the
                  requested registration.

                           (ii) Also in connection with any Shelf Registration,
                  if the Company shall file a registration statement (other than
                  in connection with the registration of securities issuable
                  pursuant to an employee stock option, stock purchase, dividend
                  reinvestment or similar plan or pursuant to a merger, exchange
                  offer or transaction of the type specified in Rule 145(a)
                  under the Securities Act) with respect to the Company's
                  securities, and the Company reasonably determines (in the case
                  of a non-underwritten offering) or the managing underwriter or
                  underwriters advise the Company (in the case of an
                  underwritten offering) that a sale or distribution of the
                  Registrable Securities would adversely affect such offering,
                  then, upon written notice by the Company, the holders of
                  Registrable Securities included in such registration shall, to
                  the extent not inconsistent with applicable law, suspend the
                  distribution of any of the Registrable Securities or any sale
                  of the Registrable Securities pursuant to Rule 144 under the
                  Securities Act during the 10-day period prior to and the
                  90-day period following the effective date of such
                  registration statement, with such 90-day period being subject
                  to early termination by the Company with the approval of the
                  managing underwriter or underwriters. The Company shall not
                  effect a suspension pursuant to this Section 2.1(l)(ii) more
                  than one time in any 12-month period.

                  (m) Shelf Take-Down Procedures. The Owners' rights to require
         a Shelf Registration shall include the right, on or after the Secondary
         Offering Date, to require one underwritten offering off that Shelf
         Registration (a "TAKE-DOWN") plus an additional number of take-downs
         equal to the number of unused Demand Offerings remaining for the Owners
         (as set forth in Section 2.1(g) hereof). One or more Owners having
         Registrable Securities included in an effective Shelf Registration may
         request an underwritten take-down, and the Company shall be obligated
         to give notice and opportunity to participate in the take-down to the
         other Owners having Registrable Securities included in that Shelf
         Registration, in accordance with the same procedures, limitations and
         allocations applicable to a Demand Request for an Immediate Offering
         Registration (with such

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         changes in those procedures, limitations and allocations as are
         necessary to reflect that it is a take-down from a Shelf Registration).
         No Owner may request a take-down for a number of that Owner's
         Registrable Securities that exceeds the number of that Owner's
         Registrable Securities already included in the effective Shelf
         Registration.

                  (n) Registration of Warrants. A registration statement filed
         pursuant to a Demand Registration or a Shelf Registration and which
         registers the resale of any Warrants shall also include the
         registration of the issuance of all shares of common stock of the
         Company issuable upon the exercise of such Warrants by any holder
         thereof who either (i) purchases such Warrants pursuant to such
         registration statement or (ii) purchases such Warrants after such
         Warrants have been previously purchased by another person pursuant to
         such registration statement.

                  2.2. Incidental Registration.

                  (a) Right to Include Registrable Securities. If the Company,
         at any time after the date of this Agreement, proposes to register any
         of its securities under the Securities Act (other than (i) in
         connection with a registration of securities issuable under any
         employee benefit, retirement or similar plan, or (ii) with respect to a
         Rule 145 transaction), whether or not for sale for its own account, and
         if notice of such transaction is not already given pursuant to Section
         2.1 above, it shall each such time give written notice to all holders
         of Registrable Securities, at least 30 days before the filing date of
         the registration statement with the Commission, of its intention to
         register such shares and of the Owners' rights under this Section 2.2.
         Upon the written request of any Owner made within 15 business days
         after the receipt of the Company's notice (which request shall specify
         that the Owner of Registrable Securities desires to include such
         Registrable Securities in an offering pursuant to this Section 2.2 and
         shall specify the number of Registrable Securities requested to be
         included in such offering), the Company shall use reasonable efforts to
         effect the registration under the Securities Act of all Registrable
         Securities which the Company has been so requested to register by the
         holders thereof ("PIGGYBACK REGISTRATION"), to the extent requisite to
         permit the disposition of the Registrable Securities so to be
         registered; provided, that if, at any time after giving written notice
         of its intention to register any securities and prior to the effective
         date of the registration statement filed in connection with such
         registration, the Company shall determine for any reason not to
         register or to delay registration of such securities, the Company may,
         at its election, give written notice of such determination to each
         holder of Registrable Securities and, thereupon, (i) in the case of a
         determination not to register, shall be relieved of its obligation to
         register any Registrable Securities in connection with such
         registration (but not from its obligation to pay the Registration
         Expenses in connection therewith), without prejudice, however, to the
         rights of any holder or holders of Registrable Securities entitled to
         do so to request that such registration be effected as a registration
         under Section 2.1(a) above, and (ii) in the case of a determination to
         delay registering, shall be permitted to delay registering any
         Registrable Securities, for the same period as the delay in registering
         such other securities; and provided further, that no Registrable
         Securities shall be included in an underwritten registration except
         Registrable Securities of the same class as those being registered
         therein. Each holder of Registrable Securities shall be permitted to
         withdraw all or part of such holder's Registrable Securities from a
         Piggyback Registration at any time before the earlier of the effective
         date of the related registration statement and the signing of a
         definitive

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         underwriting, purchase or agency agreement with the underwriters.
         Subject to Section 2.2(c) below, the Company shall use all commercially
         reasonable efforts to cause the managing underwriters of a proposed
         offering to permit the Registrable Securities requested to be included
         in the offering to be included at the same price and on no less
         favorable terms and conditions as any similar securities included
         therein. No registration effected under this Section 2.2 shall be
         deemed to have been effected pursuant to Section 2.1 above or shall
         relieve the Company of its obligation to effect any registration upon
         request under Section 2.1 above.

                  (b) Expenses. The Company shall pay all Registration Expenses
         in connection with any registration of Registrable Securities requested
         pursuant to this Section 2.2, and all Persons on whose behalf
         securities of the Company are included in such registration shall pay
         their own Selling Expenses, with joint costs allocated on the basis of
         the respective amounts of the securities then being registered on their
         behalf.

                  (c) Priority in Incidental Registrations.

                           (i) If a registration pursuant to this Section 2.2
                  was initiated as an offering of securities for sale for the
                  account of the Company (other than the Initial Secondary
                  Offering, which shall be governed by the priority provisions
                  set forth in Section 2.1(i)(i) hereof), to be distributed (on
                  a firm commitment basis) by or through one or more
                  underwriters, and if the managing underwriter of such
                  underwritten offering shall inform the Company and the Owners
                  of Registrable Securities requesting such registration by
                  letter of its belief that the number of securities requested
                  to be included in such registration will materially and
                  adversely affect the price or success of the offering, then
                  the Company shall include in such registration, to the extent
                  of the number of securities which the Company is so advised
                  can be sold in (or during the time of) such offering, first,
                  all securities proposed by the Company to be sold for its own
                  account, second, such Registrable Securities requested to be
                  included in such registration, pro rata on the basis of the
                  number of such securities so proposed to be sold and so
                  requested to be included, and third, all other securities of
                  the Company requested to be included in such registration, pro
                  rata on the basis of the number of such securities so proposed
                  to be sold and so requested to be included (and any amounts
                  above the amounts so allocated shall not be included).

                           (ii) If a registration pursuant to this Section 2.2
                  was initiated as an offering of Registrable Securities for
                  sale for the account of Owners that made a Demand Request
                  (other than the Initial Secondary Offering and the first
                  underwritten Demand Offering following the Initial Secondary
                  Offering, which shall be governed by the priority provisions
                  set forth in Sections 2.1(i)(i) and 2.1(i)(ii) hereof,
                  respectively), to be distributed (on a firm commitment basis)
                  by or through one or more underwriters, and if the managing
                  underwriter of such underwritten offering shall inform the
                  Owners of Registrable Securities that made the Demand Request
                  and the Company by letter of its belief that the number of
                  securities requested to be included in such registration will
                  materially and adversely affect the price or success of the
                  Demand Offering, then the Company shall include in such
                  registration, to the extent of the number of securities which
                  the Company is so advised can be sold in (or during

                                      -10-
<PAGE>   11

                  the time of) such offering, first, all securities proposed by
                  the Owner of Registrable Securities that made the Demand
                  Request to be sold for its own account, in accordance with the
                  provisions of Section 2.1 above (including, without
                  limitation, all such Owners who elect to participate pursuant
                  to a Demand Request given in accordance with Section
                  2.1(a)(ii)(B) hereof), second, all securities proposed by the
                  Company to be sold for its own account, third, such
                  Registrable Securities requested to be included in such
                  registration, pro rata on the basis of the number of such
                  securities so proposed to be sold and so requested to be
                  included, and fourth, all other securities of the Company
                  requested to be included in such registration, pro rata on the
                  basis of the number of such securities so proposed to be sold
                  and so requested to be included (and any amounts above the
                  amounts so allocated shall not be included).

                  2.3. Demand Registration Procedures. If and whenever the
         Company is required to use reasonable efforts to effect the
         registration of any Registrable Securities under the Securities Act as
         provided in Section 2.1 above, the Company shall as expeditiously as
         possible:

                           (i) prepare and (as soon thereafter as possible or in
                  any event no later than 60 days after the first Demand
                  Request) file with the Commission the requisite registration
                  statement to effect such registration and thereafter use
                  reasonable efforts to cause such registration statement to
                  become effective; provided, that (A) a reasonable time before
                  filing a registration statement or prospectus or other
                  offering materials, or any amendments or supplements thereto,
                  the Company will furnish to the Owners of Registrable
                  Securities to be registered and to one counsel selected by the
                  holders of a majority of the Registrable Securities included
                  in such registration (and one separate counsel for each such
                  Owner if paid for by such Owner), copies of all such documents
                  proposed to be filed, which documents will be subject to the
                  review of such counsel, and shall thereafter furnish revised
                  drafts and definitive versions of all such documents when they
                  are circulated to the working group for the Demand Offering,
                  and (B) after the filing of the registration statement, the
                  Company will promptly notify the counsel to the Owners of
                  Registrable Securities of comments received from the
                  Commission or the securities exchange or market or
                  inter-dealer quotation system, and other governmental
                  authorities as may be applicable; provided, that, in
                  connection with a Demand Offering, the Company shall not file
                  or circulate to potential investors any registration statement
                  or prospectus, or other offering materials, or any amendments
                  or supplements thereto, if the Owners of Registrable
                  Securities who hold a majority of the Registrable Securities
                  covered by such registration statement, prospectus, or other
                  offering materials (acting through their counsel), the
                  managing underwriter, or its counsel shall reasonably object,
                  in writing, on a timely basis;

                           (ii) prepare and file with the Commission, any
                  applicable securities exchange or market or inter-dealer
                  quotations system such amendments and supplements to such
                  registration statement and the prospectus used in connection
                  therewith as may be necessary to keep such registration
                  statement effective and to comply with the provisions of the
                  Securities Act with respect to the disposition of all
                  securities covered by such registration statement until such
                  time as all of such securities have been disposed of in
                  accordance with the intended methods of disposition by the
                  seller or sellers thereof set forth in such

                                      -11-
<PAGE>   12

                  registration statement; provided, however, that the Company
                  shall not be required to maintain the effectiveness of any
                  registration statement for more than 90 days or such longer
                  period as required by Section 2.1(l) hereof in the event of a
                  suspension of a registration statement (or, with respect to a
                  Shelf Registration, until the earlier of the date on which all
                  securities covered thereby have ceased to be Registrable
                  Securities or the date on which all of such securities have
                  been disposed of in accordance with the intended methods of
                  disposition by the seller or sellers thereof, subject to the
                  provisions of Section 2.1(l) above) and comply with the
                  provisions of the Securities Act, the Exchange Act, and all
                  other applicable laws with respect to the disposition of all
                  securities covered by such registration statement or other
                  offering materials during such period in accordance with the
                  intended methods of disposition by the Owners of Registrable
                  Securities set forth in such registration statement or other
                  offering materials;

                           (iii) furnish, without charge to each seller of
                  Registrable Securities covered by such registration statement,
                  such number of conformed copies of such registration statement
                  and of each such amendment and supplement thereto (in each
                  case including, without limitation, all exhibits), such number
                  of copies of the prospectus contained in such registration
                  statement (including, without limitation, each preliminary
                  prospectus and any summary prospectus) and any other
                  prospectus filed under Rule 424 under the Securities Act, in
                  conformity with the requirements of the Securities Act, and
                  such other documents, as such seller may reasonably request;

                           (iv) use reasonable efforts to obtain the withdrawal
                  of any order suspending or withdrawing the authorization for
                  an offering, the effectiveness of a registration statement, or
                  the lifting of any suspension of the qualification (or
                  exemption from qualification) of any of the Registrable
                  Securities for sale in any jurisdiction, at the earliest
                  practicable moment;

                           (v) cooperate with the Owners of Registrable
                  Securities and the managing underwriter to facilitate the
                  timely preparation and delivery of certificates representing
                  Registrable Securities to be sold, which certificates shall
                  not bear any restrictive legends and shall be in a form
                  eligible for deposit with The Depository Trust Corporation or
                  other appropriate book-entry depositary; and enable such
                  Registrable Securities to be registered in such names as the
                  managing underwriter may request at least one business day
                  prior to any sale of Registrable Securities;

                           (vi) make available for inspection by the Owners of
                  Registrable Securities, any underwriter participating in any
                  disposition pursuant to such registration statement or other
                  offering materials and any attorney, accountant or other
                  professional retained by any of the Owners of Registrable
                  Securities or underwriter (collectively, the "INSPECTORS"),
                  all financial and other records, pertinent corporate documents
                  and properties of the Company and its subsidiaries as shall be
                  reasonably necessary to enable them to exercise their due
                  diligence responsibility; cause the Company's officers,
                  directors, examiners, accountants, attorneys, employees and
                  subsidiaries to supply all information reasonably requested by
                  any such Inspectors in connection with such registration
                  statement or other offering materials; and

                                      -12-
<PAGE>   13

                  cooperate and assist in the performance of any due diligence
                  investigation by any underwriter (including, without
                  limitation, any qualified independent underwriter) or any of
                  the Owners of Registrable Securities;

                           (vii) use reasonable efforts to register or qualify
                  all Registrable Securities and other securities covered by
                  such registration statement under such other securities or
                  blue sky laws of such jurisdictions as each seller thereof
                  shall reasonably request, to keep such registration or
                  qualification in effect for so long as such registration
                  statement remains in effect, and to take any other action
                  which may be reasonably necessary or advisable to enable such
                  seller to consummate the disposition in such jurisdictions of
                  the securities owned by such seller, except that the Company
                  shall not for any such purpose be required to qualify
                  generally to do business as a foreign corporation in any
                  jurisdiction wherein it would not but for the requirements of
                  this Section 2.3(vii) be obligated to be so qualified or to
                  consent to general service of process in any such
                  jurisdiction;

                           (viii) use reasonable efforts to cause all
                  Registrable Securities covered by such registration statement
                  to be registered with or approved by such other governmental
                  agencies, authorities and the board of directors and
                  stockholders of the Company as may be necessary to enable the
                  seller or sellers thereof to consummate the disposition of
                  such Registrable Securities;

                           (ix) furnish to each seller of Registrable Securities
                  a signed counterpart, addressed to such seller (and
                  underwriters, if any), of:

                                    (A) an opinion of counsel for the Company,
                           dated the effective date of such registration
                           statement (and, if such registration includes an
                           underwritten public offering, dated the date of the
                           closing under the underwriting agreement), reasonably
                           satisfactory in form and substance to such seller
                           (which shall be deemed to be acceptable if it is
                           accepted by the underwriters), and

                                    (B) a "comfort" letter, dated the effective
                           date of such registration statement (and, if such
                           registration includes an underwritten public
                           offering, dated the date of the closing under the
                           underwriting agreement), signed by the independent
                           public accountants who have certified the Company's
                           financial statements included in such registration
                           statement,

                  in each case covering substantially the same matters with
                  respect to such registration statement (and the prospectus
                  included therein) and, in the case of the accountants' letter,
                  with respect to events subsequent to the date of such
                  financial statements, as are customarily covered in opinions
                  of issuer's counsel and in accountants' letters delivered to
                  the underwriters in underwritten public offerings of
                  securities and, in the case of the accountants' letter, such
                  other financial matters, and, in the case of the legal
                  opinion, such other legal matters, as such seller may
                  reasonably request;

                                      -13-
<PAGE>   14

                           (x) notify each seller of Registrable Securities
                  promptly: (A) when a registration statement, prospectus, or
                  other offering material or any supplement or amendment thereto
                  has been filed, and, with respect to a registration statement
                  or any post-effective amendment, when the same has become
                  effective under the Securities Act and each applicable state
                  law, (B) of any request by the Commission or any other federal
                  or state governmental authority for amendments or supplements
                  to a registration statement, or related prospectus (or other
                  legally required offering material) or for additional
                  information, (C) of the issuance by the Commission or any
                  other federal or state governmental body or agency of any
                  action, including, without limitation, a stop order,
                  suspending or withdrawing the authorization for the offering
                  or the effectiveness of a registration statement, or the
                  initiation of any proceedings for that purpose, (D) if at any
                  time the representations or warranties of the Company
                  contained in any agreement relating to an offering of
                  Registrable Securities cease to be true and correct, (E) of
                  the receipt by the Company of any notification with respect to
                  the suspension of the qualification or exemption from
                  qualification of any of the Registrable Securities for sale in
                  any jurisdiction or the initiation or threatening of any
                  proceeding for such purpose, (F) of the discovery that, or of
                  the happening of any event as a result of which, the
                  registration statement, related prospectus, other offering
                  materials or any document incorporated or deemed to be
                  incorporated therein by reference includes an untrue statement
                  of a material fact or omits to state any material fact
                  required to be stated therein or necessary to make the
                  statements therein not misleading, or that requires the making
                  of any changes in such registration statement, prospectus, or
                  other offering materials so that, in the case of the
                  registration statement, it will not contain any untrue
                  statement of a material fact or omit to state any material
                  fact required to be stated therein or necessary to make the
                  statements therein not misleading, and that in the case of the
                  prospectus, or other offering materials, it will not contain
                  any untrue statement of a material fact or omit to state any
                  material fact required to be stated therein or necessary to
                  make the statements therein, in light of the circumstances
                  under which they were made, not misleading or that such
                  document otherwise fails to comply with applicable laws, and
                  (G) of the Company's reasonable determination that a
                  post-effective amendment to a registration statement would be
                  appropriate;

                           (xi) at the request of the Requisite Holders,
                  promptly: (A) prepare and furnish to each seller a reasonable
                  number of copies of a supplement to or an amendment of the
                  prospectus as may be necessary so that, as thereafter
                  delivered to the purchasers of such securities, such
                  prospectus shall not include an untrue statement of a material
                  fact or omit to state any material fact required to be stated
                  therein or necessary to make the statements therein not
                  misleading, and (B) prepare, file with the Commission, and
                  furnish to each seller the appropriate post-effective
                  amendment;

                           (xii) otherwise use reasonable efforts to comply with
                  all applicable rules and regulations of the Commission,
                  including, without limitation, compliance with any required
                  registrations under the Exchange Act, and make available to
                  its security holders, as soon as reasonably practicable, an
                  earnings statement covering the period of at least 12 months,
                  but not more than 18 months, beginning with the first full
                  calendar month after the effective date of such registration
                  statement, which earnings statement shall satisfy the
                  provisions of

                                      -14-
<PAGE>   15

                  Section 11(a) of the Securities Act, and shall furnish to each
                  such seller at least five business days prior to the filing
                  thereof a copy of any amendment or supplement to such
                  registration statement or prospectus and shall not file any
                  thereof to which any such seller shall have reasonably
                  objected on the grounds that such amendment or supplement does
                  not comply in all material respects with the requirements of
                  the Securities Act or of the rules or regulations thereunder;

                           (xiii) provide and cause to be maintained a transfer
                  agent and registrar for all Registrable Securities covered by
                  such registration statement from and after a date not later
                  than the effective date of such registration statement;

                           (xiv) use reasonable efforts to list all Registrable
                  Securities covered by such registration statement on any
                  national securities exchange or inter-dealer quotation system
                  on which any shares of the capital stock of the Company of the
                  same class as the Registrable Securities are then listed;

                           (xv) cooperate with the underwriters with respect to
                  all roadshows and other marketing activities as may be
                  reasonably requested by the underwriters; and

                           (xvi) enter into such agreements and take such other
                  actions as the Requisite Holders shall reasonably request in
                  order to expedite or facilitate the disposition of such
                  Registrable Securities.

The Company may require each seller of Registrable Securities as to which any
registration is being effected to furnish the Company such information regarding
such seller and the distribution of such securities as the Company may from time
to time reasonably request in writing.

         Each holder of Registrable Securities agrees, by acquisition of such
Registrable Securities, that upon receipt of any notice from the Company of the
happening of any event of the kind described in clause (B) or (F) of Section
2.3(x) above, such holder will forthwith discontinue such holder's disposition
of Registrable Securities pursuant to the registration statement relating to
such Registrable Securities until such holder's receipt of the copies of the
supplemented or amended prospectus contemplated by Section 2.3(xi) above and, if
so directed by the Company, will deliver to the Company (at the Company's
expense) all copies, other than permanent file copies, then in such holder's
possession of the prospectus relating to such Registrable Securities current at
the time of receipt of such notice.

         2.4. Incidental Offering Procedures. If and whenever the Company is
required to use reasonable efforts to effect the registration of any Registrable
Securities under the Securities Act, as provided in Section 2.2 above, the
Company shall as expeditiously as possible:

                  (i) a reasonable time before filing a registration statement
         or prospectus or any amendments or supplements thereto, furnish to the
         Owners of Registrable Securities and to one counsel selected by the
         holders of a majority of the Registrable Securities included

                                      -15-
<PAGE>   16

         pursuant to Section 2.2 above (and one separate counsel for each such
         Owner if paid for by such Owner), copies of all such documents proposed
         to be filed, which documents will be subject to the review of the
         Owners of such Registrable Securities and to such counsel solely for
         the purposes of reviewing such material in connection with the Owner's
         decision of whether to continue to participate in the offering in
         accordance with the terms of this Agreement and reporting to the
         Company on a timely basis any inaccuracies with respect to information
         regarding the Owners of such Registrable Securities contained in such
         material, and the Company shall thereafter furnish revised drafts and
         definitive versions of all such documents to the Owners of such
         Registrable Securities and to such counsel when they are circulated to
         the working group for the registration, and after the filing of the
         registration statement, the Company shall promptly notify the counsel
         to the Owners of Registrable Securities of comments received from the
         Commission, or the securities exchange or market or inter-dealer
         quotation system, and other governmental authorities as may be
         applicable;

                  (ii) use all commercially reasonable efforts (A) to include
         the Registrable Securities to be included in the offering in the
         registration statement, or other appropriate offering materials for the
         type of Piggyback Registration, (B) to include the Registrable
         Securities to be included in the Piggyback Registration in any
         registration of securities to be sold in the offering otherwise being
         made with any governmental authority under state securities or blue sky
         laws or other applicable securities laws, and (C) to maintain such
         inclusion for such period as such registration statement, or other
         appropriate materials for the type of Piggyback Registration and such
         registration or qualification are otherwise maintained by the Company
         for the Person initiating the Piggyback Registration;

                  (iii) furnish without charge to the Owners of such Registrable
         Securities the number of copies of the registration statement, each
         amendment and supplement thereto (in each case including all exhibits
         thereto), the prospectus included in the registration statement
         (including, without limitation, each summary or preliminary prospectus
         or other legally required offering materials), in conformity with the
         requirements of the Securities Act and other applicable laws, all
         documents incorporated by reference into such prospectus or
         registration statement, and such other documents as the Owner of such
         Registrable Securities may reasonably request in order to facilitate
         the disposition of the Registrable Securities included in the offering;

                  (iv) notify the Owners of such Registrable Securities (A) of
         the issuance by the Commission or any other federal or state
         governmental body or agency of any action, including, without
         limitation, a stop order, suspending or withdrawing the authorization
         for the offering or the effectiveness of a registration statement, or
         the initiation of any proceedings for that purpose, and (B) if the
         Person initiating the Piggyback Registration determines to cease using
         a registration statement, prospectus or other offering document because
         of either the issuance by the Commission or any other federal or state
         governmental body or agency of a stop order or the discovery of a
         material misstatement or omission, to suspend the use of a registration
         statement, prospectus or other offering document upon receipt of such
         notification;

                                      -16-
<PAGE>   17

                  (v) notify the counsel to the Owners of such Registrable
         Securities promptly (A) when a registration statement, prospectus, or
         other offering material for the Piggyback Registration or any
         supplement or amendment thereto has been filed, and with respect to a
         registration statement or any post-effective amendment, when the same
         has become effective under the Securities Act and each applicable state
         or foreign law, (B) of any request by the Commission or any other
         federal or state governmental authority for amendments or supplements
         to such registration statement, or related prospectus (or other legally
         required offering material) or for additional information, (C) of the
         receipt by the Company of any notification with respect to the
         suspension of the qualification or exemption from qualification of any
         of the Registrable Securities for sale in any jurisdiction or the
         initiation or threatening of any proceeding for such purpose, and (D)
         of the Company's determination that a post-effective amendment to a
         registration statement would be appropriate;

                  (vi) cooperate in good faith to facilitate the timely delivery
         of certificates representing the Registrable Securities to be sold;

                  (vii) use all commercially reasonable efforts to include the
         Registrable Securities to be included in the offering in any
         underwriting agreement and listing applications as otherwise are
         entered into for the securities of the Person initiating the Piggyback
         Registration;

                  (viii) make available for inspection by the Owners of
         Registrable Securities all financial and other records, pertinent
         corporate documents and properties of the Company and its subsidiaries
         as shall be reasonably necessary to enable them to exercise their due
         diligence investigation responsibility, if any; cause the Company's
         officers, directors, examiners, accountants, attorneys, employees and
         subsidiaries to supply all information reasonably requested by any such
         Owners of Registrable Securities in connection with such registration
         statement; and cooperate and assist in the performance of any due
         diligence investigation by such Owners;

                  (ix) use best efforts to obtain a comfort letter or comfort
         letters from the Company's independent public accountants in customary
         form and covering such matters covered by comfort letter or comfort
         letters, if any, delivered to the managing underwriter, addressed to
         each of the Owners of Registrable Securities; and

                  (x) furnish to each of the Owners of Registrable Securities a
         signed legal opinion, addressed to each of the Owners of Registrable
         Securities, of counsel for the Company, dated the date of the closing
         of the underwriting or purchase agreement for the Piggyback
         Registration, in form and substance equivalent to that counsel's
         opinion, if any, to the underwriters in the offering.

                                      -17-
<PAGE>   18

         2.5. Underwritten Offerings.

         (a) Requested Underwritten Offerings. If requested by the underwriters
for any underwritten offering by holders of Registrable Securities pursuant to a
registration requested under Section 2.1 above, the Company and all sellers of
Registrable Securities to be included in such offering will enter into an
underwriting agreement with such underwriters for such offering, such agreement
to be satisfactory in substance and form to the Company and the Requisite
Holders and the underwriters and to contain such representations and warranties
by the Company and such other terms as are generally prevailing in agreements of
this type, including, without limitation, indemnities to the effect and to the
extent provided in Section 2.8 below. A holder of Registrable Securities to be
distributed by such underwriters shall not be required to make any
representations or warranties to or agreements with the Company or the
underwriters other than representations, warranties or agreements regarding such
holder, such holder's Registrable Securities and such holder's intended method
of distribution and any other representation required by law and other than
indemnification of the Company and underwriters for liabilities arising from
information furnished in writing by such holder specifically for use in the
registration statement.

         (b) Incidental Underwritten Offerings. If requested by the underwriters
for any underwritten offering by the Company or by holders of Registrable
Securities pursuant to a registration pursuant to Section 2.2 above, the Company
and all sellers of Registrable Securities to be included in such offering will
enter into an underwriting agreement with the underwriters for such offering,
such agreement to be satisfactory in substance and form to (i) the Company, and
(ii) the Requisite Holders, if the offering is pursuant to a Demand Request made
by an Owner of Registrable Securities pursuant to Section 2.1 above, and such
underwriters and to contain such representations and warranties by the Company
and such other terms as are generally prevailing in agreements of this type,
including, without limitation, indemnities to the effect and to the extent
provided in Section 2.8 below. A holder of Registrable Securities to be
distributed by such underwriters shall not be required to make any
representations or warranties to or agreements with the Company or the
underwriters other than representations, warranties or agreements regarding such
holder, such holder's Registrable Securities and such holder's intended method
of distribution and any other representation required by law and other than
indemnification of the Company and underwriters for liabilities arising from
information furnished in writing by such holder specifically for use in the
registration statement.

         2.6. Preparation; Reasonable Investigation. In connection with the
preparation and filing of each registration statement under the Securities Act
pursuant to this Agreement, the Company will give the holders of Registrable
Securities registered under such registration statement, and their counsel and
accountants, the opportunity to participate in the preparation of such
registration statement, each prospectus included therein or filed with the
Commission, and each amendment thereof or supplement thereto, and will give each
of them such access to its books and records and such opportunities to discuss
the business of the Company with its officers and the independent public
accountants who have certified its financial statements as shall be necessary,
in the opinion of such holders' counsel, to conduct a reasonable investigation
within the meaning of the Securities Act.

                                      -18-
<PAGE>   19

         2.7. Additional Rights of Owners. If any registration statement
prepared under this Agreement refers to any Owner by name or otherwise as the
holder of any securities of the Company, then such Owner shall have the right to
require (a) the insertion therein of language, in form and substance
satisfactory to such Owner, to the effect that the holding by such Owner of such
securities does not necessarily make such Owner a "controlling person" of the
Company within the meaning of the Securities Act and is not to be construed as a
recommendation by such Owner of the investment quality of the Company's debt or
equity securities covered thereby and that such holding does not imply that such
Owner will assist in meeting any future financial requirements of the Company,
or (b) in the event that such reference to such Owner by name or otherwise is
not required by the Securities Act or any rules and regulations promulgated
thereunder, the deletion of the reference to such Owner.

         2.8. Indemnification.

         (a) Indemnification by the Company. In the event of any registration of
any securities of the Company under the Securities Act, the Company will, and
hereby does, indemnify and hold harmless the seller of any Registrable
Securities covered by such registration statement, and the officers, directors,
agents, attorneys, general and limited partners, affiliates, accountants and
employees of the seller of any such Registrable Securities, each other Person
who participates in the offering or sale of such securities and each other
Person, if any, who controls such seller, within the meaning of the Securities
Act, against any losses, claims, damages or liabilities, joint or several, to
which such seller or any such director or officer or controlling person may
become subject, under the Securities Act or otherwise, insofar as such losses,
claims, damages or liabilities (or actions or proceedings, whether commenced or
threatened, in respect thereof) arise out of or are based upon any untrue
statement or alleged untrue statement of any material fact contained in any
registration statement under which such securities were registered under the
Securities Act, any preliminary prospectus, final prospectus or summary
prospectus contained therein, or any amendment or supplement thereto, or any
omission or alleged omission to state therein a material fact required to be
stated therein or necessary to make the statements therein not misleading, and
the Company will reimburse such seller and each such officer, director, agent,
attorney, general and limited partner, affiliate, accountant and employee, and
controlling person for any legal or any other expenses reasonably incurred by
them in connection with investigating or defending any such loss, claim,
liability, action or proceeding; provided, however, that the Company shall not
be liable in any such case to the extent that any such loss, claim, damage,
liability (or action or proceeding in respect thereof) or expense arises out of
or is based upon an untrue statement or alleged untrue statement or omission or
alleged omission made in such registration statement, any such preliminary
prospectus, final prospectus, summary prospectus, amendment or supplement in
reliance upon and in conformity with written information furnished to the
Company through an instrument duly executed by such seller specifically stating
that it is for use in the preparation thereof; and provided further, that the
Company shall not be liable to any Person who participates as an underwriter in
the offering or sale of Registrable Securities or any other Person, if any, who
controls such underwriter within the meaning of the Securities Act, in any such
case to the extent that any such loss, claim, damage, liability (or action or
proceeding in respect thereof) or expense arises out of such Person's failure to
send or give a copy of the final prospectus, as the same may be then
supplemented or amended, to

                                      -19-
<PAGE>   20

the Person asserting an untrue statement or alleged untrue statement or omission
or alleged omission at or prior to the written confirmation of the sale of
Registrable Securities to such Person if such statement or omission was
corrected in such final prospectus. Such indemnity shall remain in full force
and effect regardless of any investigation made by or on behalf of such seller
or any such director, officer, underwriter or controlling person and shall
survive the transfer of such securities by such seller.

         (b) Indemnification by the Sellers. In the event of any registration of
any securities of the Company under the Securities Act, each of the sellers of
Registrable Securities covered by such registration statement will, and hereby
does, indemnify and hold harmless (in the same manner and to the same extent as
set forth in Section 2.8(a) above) the Company, each director of the Company,
each officer of the Company and each other Person, if any, who controls the
Company within the meaning of the Securities Act, to the same extent as the
foregoing indemnity from the Company to the seller of Registrable Securities,
but only with respect to information furnished in writing to the Company by the
seller of Registrable Securities expressly for use in any registration
statement, prospectus or other offering materials relating to the Registrable
Securities. Such indemnity shall remain in full force and effect, regardless of
any investigation made by or on behalf of the Company or any such director,
officer or controlling Person and shall survive the transfer of such securities
by such seller.

         (c) Notices of Claims, etc. Promptly after receipt by an indemnified
party of notice of the commencement of any action or proceeding involving a
claim referred to in Section 2.8(a) or (b) above, such indemnified party will,
if a claim in respect thereof is to be made against an indemnifying party, give
written notice to the latter of the commencement of such action; provided,
however, that the failure of any indemnified party to give notice as provided
herein shall not relieve the indemnifying party of its obligations under
Sections 2.8(a) and (b) above, except to the extent that the indemnifying party
is actually prejudiced by such failure to give notice. In case any such action
is brought against an indemnified party, unless in such indemnified party's
reasonable judgment a conflict of interest between such indemnified and
indemnifying parties may exist in respect of such claim, the indemnifying party
shall be entitled to participate in and to assume the defense thereof, jointly
with any other indemnifying party similarly notified to the extent that it may
wish, with counsel reasonably satisfactory to such indemnified party, and after
notice from the indemnifying party to such indemnified party of its election so
to assume the defense thereof, the indemnifying party shall not be liable to
such indemnified party for any legal or other expenses subsequently incurred by
the latter in connection with the defense thereof other than reasonable costs of
investigation. No indemnifying party shall, without the consent of the
indemnified party, consent to entry of any judgment or enter into any settlement
which does not include as an unconditional term thereof the giving by the
claimant or plaintiff to such indemnified party of a release from all liability
in respect to such claim or litigation.

         (d) Other Indemnification. Indemnification similar to that specified in
this Section 2.8 (with appropriate modifications) shall be given by the Company
and each seller of Registrable Securities with respect to any required
registration or other qualification of securities under any Federal or state law
or regulation of any governmental authority other than the Securities Act.

                                      -20-
<PAGE>   21

         (e) Indemnification Payments. The indemnification required by this
Section 2.8 shall be made by periodic payments of the amount thereof during the
course of the investigation or defense, as and when bills are received or
expense, loss, damage or liability is incurred.

         2.9. Adjustments Affecting Registrable Securities. The Company will not
effect or permit to occur any combination or subdivision which would adversely
affect the ability of the holders of Registrable Securities to include such
Registrable Securities in any registration of its securities contemplated by
this Agreement or the marketability of such Registrable Securities under any
such registration.

         2.10. Holdback Agreement. If the Company, at any time pursuant to
Section 2.1 or 2.2 above, shall register under the Securities Act Registrable
Securities held by Owners for sale to the public pursuant to an underwritten
offering, the Company shall not, without the prior written consent of the
Majority Holders, effect any public sale or distribution of securities similar
to those being registered, or any securities convertible into or exercisable or
exchangeable for such securities, for such period as shall be determined by the
managing underwriters, which period shall not begin more than 10 days prior to
the effectiveness of the registration pursuant to which such public offering
shall be made and shall not last more than 90 days after the closing of the sale
of securities pursuant to such registration.

         2.11. Lock-Up Period. If the Company at any time shall register any of
its securities under the Securities Act in a primary underwritten offering (a)
pursuant to an Initial Secondary Offering or (b) pursuant to any other
registration, the Owners shall not sell, make any short sale of, grant any
option for the purchase of, or otherwise dispose of any Registrable Securities
(other than those Registrable Securities included in such registration) without
the prior written consent of the Company for a period as shall be determined by
the managing underwriter of such offering, which period cannot begin more than
10 days prior to the effectiveness of such registration and cannot last more
than 180 days after the effective date of such registration for the Company's
Initial Secondary Offering and 90 days for all other registrations (provided,
however, that the Owners shall not be prevented from selling their respective
Registrable Securities pursuant to this Section 2.11 more than once in any 12
consecutive month period).

         2.12. Third Party Registration Rights. The Company has not granted
demand or piggyback registration rights to any party other than the Owners of
Registrable Securities, except pursuant to the Midland Agreement.

         2.13 Decisions within a Group of Holders. Any time a specified group of
Owners (e.g. the Vista Holders, the Individual Vista Holders or the Prize
Holders) has certain rights under this Section 2, any decision or election to be
made by that group of Owners shall be made by a majority in interest of the
members of that group, except that, while Hill is a holder of Registrable
Securities, all decisions of the Individual Vista Holders shall be made by Hill.

                                      -21-
<PAGE>   22

         3. Definitions. As used herein, unless the context otherwise requires,
the following terms have the following respective meanings:

            COMMISSION: The Securities and Exchange Commission or any other
            Federal agency at the time administering the Securities Act.

            EXCHANGE ACT: The Securities Exchange Act of 1934, or any similar
            Federal statute, and the rules and regulations of the Commission
            thereunder, all as the same shall be in effect at the time.
            Reference to a particular section of the Exchange Act shall include
            a reference to the comparable section, if any, of any such similar
            Federal statute.

            HILL: C. Randall Hill, one of the Individual Vista Holders.

            INDIVIDUAL VISTA HOLDERS: The Vista Holders other than Natural Gas
            Partners II, L.P. and Natural Gas Partners III, L.P.

            INITIAL SECONDARY OFFERING: The first offering and sale by the
            Company of newly issued shares of the common stock of the Company,
            by Pioneer of shares of the common stock of the Company in an
            underwritten offering, or both, in the United States following the
            date of this Agreement pursuant to a registration statement filed
            and declared effective under the Securities Act (other than a
            registration of securities with respect to an employee benefit,
            retirement or similar plan, a Rule 145 transaction or pursuant to
            the Midland Agreement).

            MAJORITY HOLDERS: At any time, the holder or holders of more than
            50% of all Registrable Securities then outstanding.

            MIDLAND AGREEMENT: That certain Registration Rights Agreement for
            Midland Holders dated October 28, 1998, between the Company and
            certain holders of warrants to purchase shares of common stock of
            the Company.

            PERSON: A corporation, an association, a partnership, a limited
            liability company, a business, an individual, a governmental or
            political subdivision thereof or a governmental agency.

            PIONEER: Pioneer Natural Resources USA, Inc., a Delaware
            corporation.

            PRIZE HOLDERS: Pioneer and those other Owners who are identified as
            such on Exhibit A hereto, all of which were stockholders of Prize
            prior to consummation of the Merger.

            REGISTRABLE SECURITIES: Any of the common stock of the Company owned
            by an Owner or issuable to an Owner upon conversion of Series A
            Preferred Shares or upon

                                      -22-
<PAGE>   23

            exercise of any Warrants, any Warrants owned by an Owner and any
            securities issued or issuable with respect to any such common stock
            or Warrants by way of distribution or in connection with any
            reorganization or other recapitalization, merger, consolidation or
            otherwise. As to any particular Registrable Securities, once issued,
            such securities shall cease to be Registrable Securities when (a) a
            registration statement with respect to the sale of such securities
            shall have become effective under the Securities Act and such
            securities shall have been disposed of in accordance with such
            registration statement, (b) the Owner shall have sold such
            securities to the public pursuant to Rule 144 (or any successor
            provision) under the Securities Act, (c) such securities have been
            otherwise transferred, new certificates for them not bearing a
            legend restricting further transfer shall have been delivered by the
            Company and subsequent disposition of such securities shall not
            require registration or qualification under the Securities Act or
            any similar state law then in force, (d) such securities represent
            less than 5% of the issued and outstanding common stock of the
            Company and are able to be sold under Rule 144(k) (or successor
            Rule) under the Securities Act without restriction, or (e) such
            securities shall have ceased to be outstanding.

            REGISTRATION EXPENSES: All expenses incident to the Company's
            performance of or compliance with Section 2.1 and 2.2 above,
            including, without limitation, all registration, filing and National
            Association of Securities Dealers fees, all fees and expenses of
            complying with applicable laws (including, without limitation,
            securities or blue sky laws), all word processing, duplicating and
            printing expenses, messenger and delivery expenses, the fees and
            disbursements of counsel for the Company and of its independent
            public accountants, including, without limitation, the expenses of
            any special audits or "cold comfort" letters required by or incident
            to such performance and compliance, the fees and disbursements of
            one special counsel to the holders of Registrable Securities,
            premiums and other costs of policies of insurance against
            liabilities arising out of the public offering of the Registrable
            Securities being registered, the fees and expenses of any special
            experts, including independent petroleum engineers, retained by the
            Company in connection with such offering, the fees and expenses of
            any qualified independent underwriter or other independent appraiser
            participating in any offering pursuant to the Conduct Rules of the
            National Association of Securities Dealers, Inc., all travel
            expenses of the Company's officers and employees and any other
            expenses of the Company in connection with attending or hosting
            meetings with prospective purchasers of the offered securities, and
            any fees and disbursements of underwriters customarily paid by
            issuers or sellers of securities, but excluding Selling Expenses, if
            any; provided, that, in any case where Registration Expenses are not
            to be borne by the Company, such expenses shall not include salaries
            of Company personnel or general overhead expenses of the Company,
            auditing fees, premiums or other expenses relating to liability
            insurance required by underwriters of the Company or other expenses
            for the preparation of financial statements or other data normally
            prepared by the Company in the ordinary course of its business or
            which the Company would have incurred in any event.

                                      -23-
<PAGE>   24

            REQUISITE HOLDERS: With respect to any registration of Registrable
            Securities, any holder or holders of more than 50% of the
            Registrable Securities to be so registered.

            SECONDARY OFFERING DATE: The first anniversary date of the Initial
            Secondary Offering, or such earlier date on which an investment
            banking firm selected by mutual agreement of the Company and Pioneer
            determines that market conditions are favorable for another
            secondary offering of Registrable Securities.

            SECURITIES ACT: The Securities Act of 1933, or any similar Federal
            statute, and the rules and regulations of the Commission thereunder,
            as the same shall be in effect at the time. References to a
            particular section of the Securities Act shall include a reference
            to the comparable section, if any, of any such similar Federal
            statute.

            SELLING EXPENSES: Underwriting discounts and commissions and stock
            transfer taxes relating to Registrable Securities owned by selling
            holders being registered by the Company and the fees and
            disbursements paid to representatives retained by holders of
            Registrable Securities to be registered (including, without
            limitation, the fees and disbursements of legal counsel to the
            holders of such Registrable Securities, other than the one special
            counsel referred to in the definition of Registration Expenses).

            SERIES A PREFERRED SHARES: The shares of the Company's Series A 6%
            Convertible Preferred Stock issued in the Merger to Pioneer as
            holder of shares of Prize's Series A 6% Convertible Preferred Stock.

            VISTA HOLDERS: Those Owners who are identified as such on Exhibit A
            hereto, all of whom were stockholders of the Company prior to
            consummation of the Merger.

            WARRANTS: The warrants owned by the Vista Holders as of the date
            hereof that are exercisable to purchase shares of common stock of
            the Company.

         4. Rule 144 and Rule 144A: The Company shall file the reports required
to be filed by it under the Securities Act and the Exchange Act and the rules
and regulations adopted by the Commission thereunder and shall take such further
action as any holder of Registrable Securities may reasonably request, all to
the extent required from time to time to enable such holder to sell Registrable
Securities without registration under the Securities Act within the limitation
of the exemptions provided by (a) Rule 144 under the Securities Act, as such
Rule may be amended from time to time, or (b) any similar rule or regulation
hereafter adopted by the Commission. Upon the request of any holder of
Registrable Securities, the Company shall deliver to such holder a written
statement as to whether it has complied with such requirements. After any sale
of Registrable Securities pursuant to this Section 4, the Company shall, to the
extent allowed by law, cause any restrictive legends to be removed and any
transfer restrictions to be rescinded with respect to such

                                      -24-
<PAGE>   25

Registrable Securities. In order to permit the holders of Registrable Securities
to sell the same if they so desire, and Pioneer to sell Series A Preferred
Shares if it so desires, pursuant to Rule 144A promulgated by the Commission (or
any successor to such rule) ("RULE 144A"), the Company shall comply with all
rules and regulations of the Commission applicable in connection with the use of
Rule 144A. Prospective transferees of Registrable Securities and Series A
Preferred Shares that are Qualified Institutional Buyers (as defined in Rule
144A) which would be purchasing such Registrable Securities and Series A
Preferred Shares in reliance upon Rule 144A may request from the Company
information regarding the business, operations and assets of the Company. Within
five business days after receipt by the Company of any such request, the Company
shall deliver to any such prospective transferee copies of annual audited and
quarterly unaudited financial statements of the Company and such other
information as may be required to be supplied by the Company for it to comply
with Rule 144A.

         5. Amendments and Waivers. This Agreement may be amended and the
Company may take any action herein prohibited or omit to perform any act herein
required to be performed by it, only if the Company shall have obtained the
written consent to such amendment, action or omission to act, of the Majority
Holders; provided, however, that any such amendment or consent that would have a
material adverse effect on a particular Owner but would not have a similar
material adverse effect on all Owners generally or would otherwise remove an
Owner as a party to this Agreement shall require the consent of such Owner. Each
holder of any Registrable Securities at the time or thereafter outstanding shall
be bound by any consent authorized by this Section 5, whether or not such
Registrable Securities shall have been marked to indicate such consent.

         6. Nominees for Beneficial Owners. In the event that any Registrable
Securities are held by a nominee for the beneficial owner thereof, the
beneficial owner thereof may, at its election, be treated as the holder of such
Registrable Securities for purposes of any request or other action by any holder
or holders of Registrable Securities pursuant to this Agreement or any
determination of any number or percentage of Registrable Securities held by any
holder or holders of Registrable Securities contemplated by this Agreement. If
the beneficial owner of any Registrable Securities so elects, the Company may
require assurances reasonably satisfactory to it of such owner's beneficial
ownership of such Registrable Securities.

         7. Notices. All communications provided for hereunder shall be sent by
first-class mail, postage prepaid, return receipt requested, and addressed (a)
if to a party other than the Company, to such party at the address furnished to
the Company by such party, or (b) if to the Company, at 20 East 5th Street,
Suite 1400, Tulsa, OK 74103, Attention: Chairman, or at such other address, or
to the attention of such other officer, as the Company shall have furnished to
each holder of Registrable Securities at the time outstanding by a nationally
recognized commercial delivery service, charges prepaid, or by facsimile (a) if
to a party other than the Company, to such party at the facsimile number
furnished to the Company by such party, or (b) if to the Company, to (918)
582-1547; provided, however, that any such communication to the Company may
also, at the option of any of the parties hereunder, be either delivered to the
Company at its address set forth above or to any officer of the Company.

                                      -25-
<PAGE>   26

         8. Assignment. This Agreement shall be binding upon and inure to the
benefit of and be enforceable by the parties hereto and their respective
successors and assigns. In addition, and whether or not any express assignment
shall have been made, the provisions of this Agreement which are for the benefit
of the parties hereto other than the Company shall also be for the benefit of
and enforceable by any subsequent holder of any Registrable Securities, subject
to the provisions respecting the minimum numbers or percentages of Registrable
Securities required in order to be entitled to certain rights, or take certain
actions, contained herein. Pioneer shall be able to assign its rights in
connection with a transfer of its shares other than a transfer which makes such
shares cease to be Registrable Securities. In the event of an assignment by
Pioneer of its Registrable Securities, the rights of Pioneer hereunder (a) shall
not be expanded as a result, and (b) shall be exercised by the holders of a
majority in interest of the Registrable Securities originally held by Pioneer.

         9. Termination. This Agreement shall terminate when no Registrable
Securities remain outstanding.

         10. Descriptive Headings. The descriptive headings of the several
sections and paragraphs of this Agreement are inserted for reference only and
shall not limit or otherwise affect the meaning hereof. References herein to
Sections are references to Sections of this Agreement, except as otherwise
indicated.

         11. Specific Performance. The parties hereto recognize and agree that
money damages may be insufficient to compensate the holders of any Registrable
Securities for breaches by the Company of the terms hereof and, consequently,
that the equitable remedy of specific performance of the terms hereof will be
available in the event of any such breach.

         12. Governing Law. This Agreement shall be construed and enforced in
accordance with, and the rights of the parties shall be governed by, the laws of
the State of Delaware.

         13. Counterparts. This Agreement may be executed simultaneously in any
number of counterparts, each of which shall be deemed an original, but all such
counterparts shall together constitute one and the same instrument.

         14. Entire Agreement. This Agreement constitutes the entire agreement
among the parties regarding the subject matter hereof and supersedes all prior
understandings and agreements regarding such matters, including, without
limitation, the Prior Prize Agreement and the Prior Vista Agreement.

                                      -26-
<PAGE>   27

         IN WITNESS WHEREOF, the parties have duly executed and delivered this
Agreement or have caused this Agreement to be executed and delivered by their
respective officers thereunto duly authorized as of the date first above
written.

PRIZE ENERGY CORP.

By: /s/ Philip B. Smith
   ------------------------------------------
   Philip B. Smith
   Chairman and Chief Executive Officer

NATURAL GAS PARTNERS V, L.P.
By: G.F.W. Energy V, L.P., general partner
By: GFW V, L.L.C., general partner

By: /s/ Kenneth A. Hersh
   ------------------------------------------
   Kenneth A. Hersh, Authorized Member

/s/ Philip B. Smith
---------------------------------------------
Philip B. Smith, Trustee of the Philip B.
Smith Revocable Trust Dated July 25, 1994

/s/ Philip B. Smith
---------------------------------------------
Philip B. Smith, Trustee of the Scott C. Smith
Irrevocable Trust Dated January 15, 1996

/s/ Philip B. Smith
---------------------------------------------
Philip B. Smith, Trustee of the Laura E. Smith
Irrevocable Trust Dated January 15, 1996

/s/ Lon C. Kile
---------------------------------------------
Lon C. Kile

/s/ Monica L. Griffin
---------------------------------------------
Monica L. Griffin

PIONEER NATURAL RESOURCES
USA, INC.

By: /s/ Mark L. Withrow
---------------------------------------------
Mark L. Withrow
Executive Vice President

VISTA ENERGY RESOURCES, INC.

By: /s/ C. Randall Hill
   ------------------------------------------
   C. Randall Hill
   Chairman and Chief Executive Officer

NATURAL GAS PARTNERS II, L.P.
By: G.F.W. Energy II, L.P., general partner
By: GFW II, L.L.C., general partner

By: /s/ Kenneth A. Hersh
   ------------------------------------------
   Kenneth A. Hersh, Authorized Member

NATURAL GAS PARTNERS III, L.P.
By: Rainwater Energy Investors, L.P., general partner
By: GFW III, L.L.C., general partner

By: /s/ Kenneth A. Hersh
   ------------------------------------------
   Kenneth A. Hersh, Authorized Member

/s/ Thomas O. Hicks
---------------------------------------------
Thomas O. Hicks, Individually

/s/ Thomas O. Hicks
---------------------------------------------
Thomas O. Hicks, Trustee of each of the Thomas O. Hicks, Jr. 1984 Trust, the
Mack H. Hicks 1984 Trust, the John A. Hicks 1984 Trust, and the Robert B. Hicks
1984 Trust

/s/ John R. Muse
---------------------------------------------
John R. Muse

                                      -27-
<PAGE>   28

/s/ Jack D. Furst
---------------------------------------------
Jack D. Furst

/s/ Lawrence D. Stuart, Jr.
---------------------------------------------
Lawrence D. Stuart, Jr.

/s/ R. Scott Cohen
---------------------------------------------
R. Scott Cohen

/s/ Jerred G. Blanchard, Jr.
---------------------------------------------
Jerred G. Blanchard, Jr.

/s/ David A. Spuria
---------------------------------------------
David A. Spuria, as Trustee of the Roberts
Children's Trust

/s/ John P. Lewis
---------------------------------------------
John P. Lewis

/s/ Warren L. Gray
---------------------------------------------
Warren L. Gray

/s/ R. Cory Richards
---------------------------------------------
R. Cory Richards

/s/ Steven D. Gray
---------------------------------------------
Steven D. Gray

/s/ C. Randall Hill
---------------------------------------------
C. Randall Hill

/s/ Leo Gallegos
---------------------------------------------
Leo Gallegos

/s/ John Dollahan
---------------------------------------------
John Dollahan

/s/ D. Keith Mills
---------------------------------------------
D. Keith Mills

/s/ Russell Wickman
---------------------------------------------
Russell Wickman

                                      -28-
<PAGE>   29

                                                                       EXHIBIT A

                                     OWNERS

<TABLE>
<CAPTION>

           PRIZE HOLDERS                                              VISTA HOLDERS
<S>                                                             <C>
Natural Gas Partners V, L.P.                                    Natural Gas Partners II, L.P.

Philip B. Smith, Trustee of the Philip B.                       Natural Gas Partners III, L.P
  Smith Revocable Trust Dated July 25, 1994

Philip B. Smith, Trustee of the Scott C. Smith                  Thomas O. Hicks, Individually
  Irrevocable Trust Dated January 15, 1996

Philip B. Smith, Trustee of the Laura E.                        Thomas O. Hicks, Trustee of each of the
  Smith Irrevocable Trust Dated January 15, 1996                  Thomas O. Hicks, Jr. 1984 Trust, the
                                                                  Mack H. Hicks 1984 Trust, the John A. Hicks
Lon C. Kile                                                       1984 Trust, and the Robert B. Hicks 1984 Trust

Monica L. Griffin                                               John R. Muse

Pioneer Natural Resources USA, Inc.                             Jack D. Furst

                                                                Lawrence D. Stuart, Jr.

                                                                R. Scott Cohen

                                                                Jerred G. Blanchard, Jr.

                                                                David A. Spuria, as Trustee of the Roberts
                                                                  Children's Trust

                                                                John P. Lewis

                                                                Warren L. Gray

                                                                R. Cory Richards

                                                                Steven D. Gray

                                                                C. Randall Hill

                                                                Leo Gallegos

                                                                John Dollahan

                                                                D. Keith Mills

                                                                Russell Wickman
</TABLE>

                                      A-1<PAGE>   1
                                                                     EXHIBIT 4.2

                  CERTIFICATE OF DESIGNATION, VOTING POWERS AND
                        RIGHTS OF SERIES A 6% CONVERTIBLE
                 PREFERRED STOCK OF VISTA ENERGY RESOURCES, INC.

     Vista Energy Resources, Inc., a corporation organized and existing under
the laws of the State of Delaware (the "CORPORATION"), DOES HEREBY CERTIFY:

     That, pursuant to authority conferred upon the Board of Directors by the
Corporation's Certificate of Incorporation, as amended, and pursuant to the
provisions of Section 151 of the Delaware General Corporation Law, as amended,
the Board of Directors, by written consent dated as of February 8, 2000,
unanimously adopted the following resolution providing for the creation and
issuance of a series of shares of the Corporation's authorized preferred stock
designated as "Series A 6% Convertible Preferred Stock":

     RESOLVED, that a new series of the Corporation's authorized but unissued
preferred stock be, and the same hereby is, established and designated, and that
the designation and amount thereof, and the relative rights, preferences,
qualifications, limitations and restrictions thereof, are as follows:

     SECTION 1. DESIGNATION, NUMBER OF SHARES AND STATED VALUE OF SERIES A
PREFERRED STOCK. There is hereby authorized and established a series of the
Corporation's preferred stock, par value $0.01 per share, that shall be
designated as "Series A 6% Convertible Preferred Stock" ("SERIES A PREFERRED"),
and the number of shares constituting such series shall be 5,000,000. Such
number of shares may be increased, but not decreased, by resolution adopted by
the Board of Directors of the Corporation. The "STATED VALUE" per share of
Series A Preferred initially shall be equal to $7.81 (which amount shall be
proportionately adjusted in the case of recapitalizations, stock splits, stock
dividends, combinations of shares or similar matters directly affecting the
Series A Preferred).

     SECTION 2. DEFINITIONS. In addition to the definitions set forth elsewhere
herein, the following terms shall have the meanings indicated:

     "BUSINESS DAY" shall mean any day other than a Saturday, Sunday or a day on
which banking institutions in New York, New York, are authorized or obligated by
law or executive order to close.

     "CLOSING PRICE" with respect to a particular security on any Trading Day
shall mean the last reported sales price, regular way, for such security on such
Trading Day, or, in case no sale takes place on such day, the average of the
closing bid and ask prices, regular way, on such Trading Day, in either case as
reported in the principal consolidated transaction reporting system with respect
to securities listed or admitted to trading on the American Stock Exchange or
the New York Stock Exchange or, if not listed or admitted to trading on the
American Stock Exchange or the New York Stock Exchange, as reported in the
principal consolidated transaction reporting system with respect to securities
listed on the principal national securities exchange on which such security is
listed or

<PAGE>   2
admitted to trading or, if such security is not listed or admitted to trading on
any national securities exchange, the last quoted price as reported by The
Nasdaq Stock Market or such other system then in use.

     "COMMON STOCK" shall mean the common stock, par value $0.01 per share, of
the Corporation.

     "CONVERSION PRICE" shall mean the conversion price per share of Common
Stock into which Series A Preferred is convertible, as such conversion price may
be adjusted pursuant to Section 9 hereof. The initial Conversion Price shall be
$7.81.

     "JUNIOR SECURITIES" means the Common Stock or any other series of stock
issued by the Corporation ranking junior to the Series A Preferred in payment of
dividends or distributions or upon liquidation, dissolution or winding-up of the
Corporation.

     "MARKET PRICE" per share of Common Stock as of any date shall mean (i) if
the Common Stock is listed or admitted to trading on a national securities
exchange or The Nasdaq Stock Market, the average of the daily Closing Prices for
a period of 30 consecutive Trading Days ending on such date, or (ii) if the
Common Stock is not then so listed or admitted, the fair market value per share
of the Common Stock as reasonably determined by an investment banking firm
mutually acceptable to the Corporation and the holders of shares of Series A
Preferred.

     "ORIGINAL ISSUE DATE" shall mean the date on which shares of Series A
Preferred are first issued.

     "PARITY SECURITY" means any class or series of stock issued by the
Corporation ranking on a parity with the Series A Preferred in payment of
dividends or distributions or upon liquidation, dissolution or winding-up of the
Corporation.

     "PAYABLE-IN-KIND" or "PAID-IN-KIND" when used in reference to any dividend
payable on the shares of Series A Preferred means payment of the dividend by
issuance of that number of additional shares of Series A Preferred that has an
aggregate Stated Value equal to the dollar amount of such dividend then payable.
In lieu of any fractional share of Series A Preferred Stock to which a holder of
Series A Preferred Stock would otherwise be entitled, such holder shall receive
the nearest whole share of Series A Preferred Stock (i.e. if less than .5
rounded down, and if .5 or more rounded up). Shares of Series A Preferred issued
as dividends Payable-in-Kind shall be duly authorized, validly issued and
nonassessable and, upon issuance, shall have rights (including without
limitation dividend, voting, conversion and redemption rights) identical to the
outstanding shares of Series A Preferred in respect of which they are issued.

     "PERSON" means any individual, corporation, association, partnership, joint
venture, limited liability company, trust, estate, or other entity or
organization.

                                       -2-
<PAGE>   3
     "SENIOR SECURITIES" means any class or series of stock, or any class or
series of debt or debt security convertible or exchangeable into any class or
series of stock, issued by the Corporation ranking senior to the Series A
Preferred in payment of dividends or distributions or upon liquidation,
dissolution or winding-up of the Corporation.

     "TRADING DAY" with respect to any security means (i) if such security is
listed or admitted for trading on any national securities exchange, a day on
which such national securities exchange is open for trading, or (ii) if such
security is not listed or admitted to trading on any national securities
exchange, a Business Day.

     "UNDERLYING COMMON STOCK" means at any time, with respect to any share of
Series A Preferred, the aggregate number of shares of Common Stock into which
such share is then convertible pursuant to Section 9 hereof.

     SECTION 3. DIVIDENDS AND DISTRIBUTIONS.

          (a) The holders of outstanding shares of Series A Preferred shall be
     entitled to receive, as and when declared by the Corporation, out of funds
     of the Corporation legally available for the payment of dividends,
     preferential quarterly dividends at the times and at the rates provided for
     in this Section 3. Dividends on shares of the Series A Preferred shall be
     cumulative and shall accrue whether or not there shall be (at the time such
     dividend becomes payable or at any other time) profits, surplus or other
     funds of the Corporation legally available for the payment of dividends.

          (b) Dividends shall accrue on each outstanding share of Series A
     Preferred at the rate of six percent (6%) per annum of the Stated Value
     (the "DIVIDEND RATE") of such share. Dividends shall be payable quarterly,
     in arrears, as of the last Business Day of each December, March, June and
     September, commencing with March 2000 (each, a "REGULAR DIVIDEND PAYMENT
     DATE"). Dividends shall also be payable on any Redemption Date and on the
     final distribution date relating to the dissolution, liquidating or winding
     up of the Corporation (each such date, together with each Regular Dividend
     Payment Date, is a "DIVIDEND PAYMENT DATE").

          (c) Dividends on outstanding shares of Series A Preferred shall be
     Payable-in-Kind during the period (the "EXCLUSIVE PIK PERIOD") beginning on
     the Original Issue Date and ending on the earlier of (i) the Dividend
     Payment Date on December 31, 2001, and (ii) the liquidation, dissolution or
     winding up of the Corporation (in connection with the bankruptcy or
     insolvency of the Corporation or otherwise). After the Exclusive PIK
     Period, dividends on the shares of Series A Preferred shall be
     Payable-in-Kind or, at the Corporation's option, payable in cash.

          (d) The amount of dividends payable on each Dividend Payment Date
     shall be determined by applying the Dividend Rate from but excluding the
     immediately preceding

                                       -3-
<PAGE>   4
     Dividend Payment Date (or from but excluding the date of issuance of shares
     of Series A Preferred, with respect to the first dividend period) to and
     including the Dividend Payment Date.

          (e) Notwithstanding the foregoing or anything else herein to the
     contrary, however, dividends payable on any Redemption Date (as defined in
     Section 6(c) hereof) or the final distribution date relating to the
     dissolution, liquidation or winding up of the Corporation, shall be payable
     in cash only. If a Dividend Payment Date does not occur on a Regular
     Dividend Payment Date, dividends shall be calculated on the basis of the
     actual number of days elapsed from but excluding the immediately preceding
     Regular Dividend Payment Date to and including such non-Regular Dividend
     Payment Date. Dividends payable on the shares of Series A Preferred for any
     period of less than a full quarterly dividend period shall be computed on
     the basis of a 360-day year comprised of twelve 30-day months.

          (f) Dividends payable on each Dividend Payment Date shall be paid to
     record holders of the shares of Series A Preferred as they appear on the
     books of the Corporation at the close of business on the 10th Business Day
     immediately preceding the respective Dividend Payment Date or on such other
     record date as may be fixed by the Board of Directors of the Corporation in
     advance of a Dividend Payment Date, provided that no such record date shall
     be less than 10 nor more than 60 calendar days preceding such Dividend
     Payment Date.

          (g) So long as any shares of Series A Preferred are outstanding:

               (i) No dividend or other distribution shall be declared or paid,
          or set apart for payment, on or in respect of, any Junior Securities
          (other than dividends or distributions payable in shares of Junior
          Securities or in rights to purchase Junior Securities), nor shall any
          Junior Securities be redeemed, purchased or otherwise acquired for any
          consideration (or any money be paid to a sinking fund or otherwise set
          apart for the purchase or redemption of any such Junior Securities)
          unless full cumulative dividends on all outstanding shares of Series A
          Preferred and any Parity Securities have been or contemporaneously are
          declared and paid for all dividend periods terminating on or prior to
          the date set for payment of such dividend.

               (ii) No dividend or other distribution, except as described in
          the next succeeding sentence, shall be declared or paid, or set apart
          for payment, on or in respect of, Series A Preferred or any Parity
          Securities for any period unless full cumulative dividends on all
          outstanding shares of Series A Preferred and any Parity Securities
          have been or contemporaneously are declared and paid for all dividend
          periods terminating on or prior to the date set for payment of such
          dividend. When dividends are not paid in full, as aforesaid, on the
          shares of Series A Preferred and any Parity Securities, all dividends
          declared upon such Parity Securities shall be

                                      -4-
<PAGE>   5
          declared and paid pro rata so that the amounts of dividends per share
          declared and paid on the shares of Series A Preferred and such Parity
          Securities shall in all cases bear to each other the same ratio that
          unpaid dividends per share on the Series A Preferred and on such
          Parity Securities bear to each other.

               (iii) No shares of Series A Preferred or any Parity Securities
          shall be redeemed, purchased or otherwise acquired for any
          consideration (or any money be paid to a sinking fund or otherwise set
          apart for the purchase or redemption of any such Parity Security) by
          the Corporation unless the full cumulative dividends on all
          outstanding shares of Series A Preferred shall have been or
          contemporaneously are declared and paid for all dividend periods
          terminating on or prior to the date on which such redemption, purchase
          or other payment is to occur.

               (iv) No dividend or other distribution of cash or debt shall be
          declared or paid, or set apart for payment, on or in respect of, any
          Junior Securities, nor shall any Junior Securities be redeemed,
          purchased or otherwise acquired for any cash or debt consideration (or
          any money or debt paid to a sinking fund or otherwise set apart for
          the purchase or redemption of any Junior Securities) unless full
          cumulative dividends on all outstanding shares of Series A Preferred
          have been or contemporaneously are declared and paid in cash for all
          dividend periods terminating on or prior to the date set for payment
          of such dividend or distribution.

               (v) No dividend or other distribution of cash or debt shall be
          declared or paid, or set apart for payment, on or in respect of, any
          Parity Securities unless full cumulative dividends on all outstanding
          shares of Series A Preferred have been or contemporaneously are
          declared and paid in cash for all dividend periods terminating on or
          prior to the date set for payment of such dividend or distribution. No
          Parity Securities be redeemed, purchased or otherwise acquired for any
          cash or debt consideration (or any money or debt paid to a sinking
          fund or otherwise set apart for the purchase or redemption of any
          Parity Securities) unless the Series A Preferred shall have been
          called for redemption pursuant to Section 6 hereof and the full
          Redemption Price (as defined in Section 6(b) hereof) shall have been
          or contemporaneously is paid in cash on or prior to the date set for
          payment of such dividend or distribution.

     SECTION 4. CERTAIN COVENANTS AND RESTRICTIONS. So long as any shares of
Series A Preferred are outstanding:

          (a) The Corporation shall at all times reserve and keep available for
     issuance upon the conversion of the shares of Series A Preferred as
     provided in Section 6 and Section 9 hereof, respectively, such number of
     its authorized but unissued shares of Common Stock as will be sufficient to
     permit the conversion of all outstanding shares of Series A Preferred and
     all other securities and instruments convertible into shares of Common
     Stock, and shall

                                      -5-
<PAGE>   6

     take all reasonable action within its power required to increase the
     authorized number of shares of Common Stock necessary to permit the
     conversion of all outstanding shares of Series A Preferred and all such
     other securities and instruments convertible into shares of Common Stock.

          (b) The Corporation covenants and agrees that all shares of Common
     Stock that may be issued upon exercise of the conversion rights of shares
     of Series A Preferred will, upon issuance, be duly authorized, valid
     issued, fully-paid and nonassessable.

          (c) Prior to the delivery of any securities which the Corporation
     shall be obligated to deliver upon payment of dividends Payable-in-Kind or
     conversion of the Series A Preferred, the Corporation will endeavor to
     comply with all federal and state securities laws and regulations
     thereunder requiring the registration of such securities with, or any
     approval of or consent to the delivery of such securities by, any
     governmental authority.

          (d) The Corporation shall pay all taxes and other governmental charges
     (other than any income or franchise taxes), documentary stamp or similar
     issue or transfer taxes that may be imposed with respect to the issue or
     delivery of the Series A Preferred (or any other securities issued on
     account of the Series A Preferred pursuant hereto) or shares of Common
     Stock upon conversion of Series A Preferred or payment of dividends
     Payable-in-Kind as provided herein or otherwise. The Corporation shall not
     be required, however, to pay any tax or other charge imposed in connection
     with any transfer involved in the issue of any certificate for shares of
     Common Stock in any name other than that of the registered holder of the
     shares of the Series A Preferred surrendered in connection with the
     conversion thereof or otherwise, and, in such case, the Corporation shall
     not be required to issue or deliver any stock certificate until such tax or
     other charge has been paid, or it has been established to the Corporation's
     satisfaction that no tax or other charge is due.

     SECTION 5. LIQUIDATION PREFERENCE.

          (a) In the event of any liquidation, dissolution or winding-up of the
     Corporation (in connection with the bankruptcy or insolvency of the
     Corporation or otherwise), whether voluntary or involuntary, before any
     payment or distribution of the assets of the Corporation (whether capital
     or surplus) shall be made to or set apart for the holders of shares of any
     Junior Securities, the holders of the shares of Series A Preferred shall be
     entitled to receive an amount per share in cash equal to the Stated Value
     per share held by them, plus an amount in cash equal to the full cumulative
     dividends accrued and unpaid thereon, to the date of such payment, whether
     or not declared. No payment on account of any such liquidation, dissolution
     or winding-up of the Corporation shall be paid to the holders of the shares
     of Series A Preferred or the holders of any Parity Securities unless there
     shall be paid at the same time to the holders of the shares of Series A
     Preferred and the holders of any Parity Securities proportionate amounts
     determined ratably in proportion to the full preferential amounts to which
     the holders of all outstanding shares of Series A Preferred and the holders

                                      -6-
<PAGE>   7

     of all such outstanding Parity Securities are respectively entitled with
     respect to such distribution (but only to the extent of such preferential
     amounts). For purposes of this Section 5, neither a consolidation or merger
     of the Corporation with one or more partnerships, corporations or other
     entities nor a sale, lease, exchange or transfer of all or any substantial
     part of the Corporation's assets for cash, securities or other property
     shall be deemed to be a liquidation, dissolution or winding-up of the
     Corporation, whether voluntary or involuntary.

          (b) After payment of the full amount of the liquidation preference to
     which the holders of shares of Series A Preferred are entitled, such
     holders will not be entitled to any further participation in any
     distribution of assets of the Corporation.

          (c) Written notice of any liquidation, dissolution or winding-up of
     the Corporation, stating the payment date or dates when and the place or
     places where the amounts distributable in such circumstances shall be
     payable, shall be given by first class mail, postage prepaid, not less than
     15 days prior to any payment date stated therein, to the holders of record
     of the shares of Series A Preferred at their respective addresses as the
     same shall appear in the records of the Corporation.

     SECTION 6. REDEMPTION. The outstanding shares of Series A Preferred are
subject to redemption in accordance with the following provisions:

          (a) Subject to the terms hereof, the Corporation may at its option
     elect to redeem outstanding shares of Series A Preferred, in whole or in
     part (pro-rata among the outstanding shares), on any Business Day if both
     (i) the average of the Closing Prices of the Corporation's Common Stock
     during any period of at least 30 consecutive Trading Days during the
     preceding 60 Trading Days shall have exceeded 120% of the Conversion Price,
     and (ii) the Closing Price per share of the Corporation's Common Stock on
     the Trading Day immediately preceding the day on which such notice is given
     shall have equaled or exceeded 110% of the Conversion Price.

          (b) The redemption price per share for Series A Preferred (the
     "REDEMPTION PRICE") shall be equal to the Stated Value plus an amount equal
     to the aggregate dollar amount of all accrued and unpaid dividends through
     the Redemption Date. The Redemption Price shall be paid in cash from any
     source of funds legally available therefor.

          (c) The Business Day designated by the Corporation for the redemption
     of shares of Series A Preferred is referred to herein as the "REDEMPTION
     DATE." Not less than 60 days nor more than 75 days prior to the Redemption
     Date, a notice specifying the time and place of such redemption shall be
     given by first class mail, postage prepaid, to the holders of record of the
     shares of Series A Preferred to be redeemed at their respective addresses
     as the same shall appear on the books of the Corporation (but no failure to
     mail such notice or any defect therein shall affect the validity of the
     proceedings for redemption except as to the

                                      -7-
<PAGE>   8
     holder to whom the Corporation has failed to mail such notice or except as
     to the holder whose notice was defective), calling upon each such holder of
     record to surrender to the Corporation on the Redemption Date at the place
     designated in such notice such holder's certificate or certificates
     representing the then outstanding shares of Series A Preferred held by such
     holder. Each such notice of redemption shall specify the Redemption Date,
     the Redemption Price, the place or places of payment, that payment will be
     made upon presentation and surrender of the shares of Series A Preferred,
     that dividends will cease to accrue on such shares on and after the
     Redemption Date, the then-effective Conversion Price pursuant to Section 9
     hereof, and that the right of holders to convert shares of Series A
     Preferred will terminate at the close of business on the Business Day
     immediately preceding the Redemption Date (unless the Corporation defaults
     in the payment of the Redemption Price). On or after the Redemption Date,
     each holder of shares of Series A Preferred called for redemption shall
     surrender such holder's certificate or certificates for such shares to the
     Corporation at the place designated in the redemption notice and shall
     thereupon be entitled to receive payment of the Redemption Price in the
     manner set forth in Section 6(b) above. If the redemption is delayed for
     any reason, dividends shall continue to accrue on the shares of Series A
     Preferred outstanding, and shall be added to and become a part of the
     Redemption Price of such shares, until the Redemption Price, as so
     adjusted, for such shares is paid in full.

          (d) Notwithstanding the foregoing, if notice of redemption has been
     given pursuant to Sections 6(a) and 6(c) hereof and any holder of the
     Series A Preferred shall, before the close of business on the Business Day
     immediately preceding the Redemption Date, give notice to the Corporation
     pursuant to Section 9(b) hereof of the conversion of any or all of the
     shares to be redeemed held by that holder, then (i) the Corporation shall
     not have the right to redeem those shares for which the conversion notice
     has been given, (ii) the holder shall not be entitled to payment of the
     Redemption Price with respect to those shares, (iii) the conversion of
     those shares shall become effective as provided in Section 9 hereof, and
     (iv) any funds that have been deposited for the payment of the Redemption
     Price of those shares shall be returned to the Corporation immediately
     after such conversion.

     SECTION 7. SHARES TO BE RETIRED. All shares of Series A Preferred
repurchased, redeemed, converted or otherwise acquired by the Corporation shall
be retired and cancelled and shall be restored to the status of authorized but
unissued shares of Preferred Stock, without designation as to series, and may
thereafter be reissued (subject to the provisions of Section 8 hereof).

     SECTION 8. VOTING RIGHTS.

          (a) Except as otherwise provided in this Section 8 or required by law
     or any provision of the Certificate of Incorporation of the Corporation,
     the holders of the shares of Series A Preferred shall vote together with
     the shares of Common Stock as a single class at any annual or special
     meeting of stockholders of the Corporation upon the following basis:

                                      -8-
<PAGE>   9

     each holder of shares of Series A Preferred shall be entitled to such
     number of votes for the shares of Series A Preferred held by such holder on
     the record date fixed for such meeting as shall be equal to the whole
     number of shares of Underlying Common Stock with respect to such shares of
     Series A Preferred immediately after the close of business on the record
     date fixed for such meeting. In all cases where the holders of separate
     classes or series of the Corporation's capital stock have the right to vote
     separately as a class, the holders of Series A Preferred shall be entitled
     to one vote for each such share held by them.

          (b) For so long as any shares of Series A Preferred remain
     outstanding, the Corporation shall not, without the affirmative vote or
     consent of the holders of a majority of the shares of Series A Preferred
     voting together as a single class, authorize, create or issue, or increase
     the authorized or issued amount of, any class or series of stock of Senior
     Securities, Parity Securities or Series A Preferred (except through payment
     of dividends Payable-in-Kind on the Series A Preferred), or any security
     convertible into or exchangeable for Senior Securities or Parity Securities
     or reclassify or modify any Junior Securities so as to become Parity
     Securities or Senior Securities.

          (c) Shares of Series A Preferred acquired by a subsidiary of the
     Corporation shall have no voting rights.

          (d) For so long as any shares of Series A Preferred remain
     outstanding, the Corporation shall not, without the affirmative vote or
     consent of the majority (unless a higher percentage shall then be specified
     by law) of the shares of Series A Preferred voting together as a single
     class, merge or consolidate with or into any other Person or permit any
     other Person to merge with or into the Corporation, unless each share of
     Series A Preferred shall remain outstanding and unaffected or shall be
     converted into or exchanged for convertible preferred stock of the
     surviving entity (and, in the case of triangular mergers, with conversion
     rights into the common equity of the ultimate parent entity) having powers,
     preferences and relative participating, optional and other rights, and
     qualifications, limitations and restrictions thereof identical to a share
     of Series A Preferred, and unless the affirmative vote or consent of the
     holders of all the shares of Series A Preferred voting together as a single
     class shall have been obtained if such exchange, merger or consolidation
     shall result in the existence of Senior Securities or Parity Securities
     (treating securities issued by the surviving entity as having been issued
     by the Corporation) other than those previously approved pursuant to
     Section 8(b) hereof; provided, however, that the voting rights with respect
     to this Section 8(d) shall be exercisable only by the original holder of
     the Series A Preferred and such voting rights shall terminate on the first
     date on which such original holder no longer owns shares of Series A
     Preferred which constitute at least 14.03% of the total issued and
     outstanding shares of Common Stock of the Corporation (based upon the
     number of shares of Common Stock into which the shares of Series A
     Preferred are then convertible and deeming the shares of Series A Preferred
     to be converted into issued and outstanding shares of Common Stock for the
     purpose of such computation).

                                     -9-
<PAGE>   10
     SECTION 9. CONVERSION RIGHTS. Holders of shares of Series A Preferred shall
have the right to convert all or a portion of such shares into shares of Common
Stock, as follows:

          (a) Subject to and upon compliance with the provisions of this Section
     9, shares of Series A Preferred shall be convertible at the option of the
     holder thereof into duly authorized, validly issued, fully paid and
     non-assessable shares of Common Stock. The number of shares of Common Stock
     deliverable upon conversion of one share of Series A Preferred shall be
     determined by dividing the Stated Value of such share of Series A Preferred
     by the Conversion Price then in effect (i.e., prior to any adjustment of
     the Conversion Price, one share of Common Stock will be issued for each
     share of Series A Preferred surrendered for conversion). In lieu of any
     fractional share of Common Stock to which a holder of Series A Preferred
     Stock would otherwise be entitled, such holder shall receive the nearest
     whole share of Common Stock (i.e., if less than .5 rounded down, and if .5
     or more rounded up). A holder of Series A Preferred may provisionally
     convert any shares of Series A Preferred that are the subject of a pending
     registration with the Securities and Exchange Commission. Unless the holder
     states an earlier time in the conversion notice to the Corporation, a
     provisional conversion will be effective only as of the closing of the
     holder's sale of Common Stock issuable upon conversion of Series A
     Preferred made pursuant to such an effective registration statement (and
     only with respect to the shares so sold); otherwise, such shares of Series
     A Preferred shall be outstanding as Series A Preferred for all purposes
     hereunder (including accrual and payment of dividends) during any period in
     which a provisional conversion is pending.

          (b) The conversion of shares of Series A Preferred may be effected by
     the holder thereof by the surrender of the certificate for such shares to
     the Corporation at the principal office of the Corporation. If the
     conversion is to be provisional as provided in Section 9(a) above, the
     holder shall also deliver a notice to the Corporation with a statement to
     that effect. If any shares of Series A Preferred are called for redemption
     pursuant to Section 6 hereof, such right of conversion shall cease and
     terminate as to the shares called for redemption at the close of business
     on the Business Day immediately preceding the Redemption Date, unless the
     Corporation shall default in the payment of the Redemption Price, in which
     event such conversion right shall remain in effect until full payment of
     the Redemption Price has been made.

          (c) As promptly as practicable after the surrender of shares of Series
     A Preferred for conversion (unless the shares are surrendered in a
     provisional conversion as provided in Section 9(a) hereof), the Corporation
     shall issue and deliver or cause to be issued and delivered to the holder
     of such shares certificates representing the number of fully paid and
     non-assessable shares of Common Stock into which such shares of Series A
     Preferred have been converted in accordance with the provisions of this
     Section 9. In lieu of any fractional share of Common Stock to which a
     holder of Series A Preferred Stock would otherwise be entitled, such holder
     shall receive the nearest whole share of Common Stock (i.e., if less than
     .5 rounded down, and if .5 or more rounded up). Subject to the following
     provisions of this

                                      -10-
<PAGE>   11

     Section 9, and, except with respect to provisional conversions, such
     conversion shall be deemed to have been made as of the close of business on
     the date on which the shares of Series A Preferred shall have been
     surrendered for conversion in the manner herein provided, so that all
     rights of the holder of the shares of Series A Preferred so surrendered
     shall cease at such time, and the person or persons entitled to receive the
     shares of Common Stock upon conversion thereof shall be treated for all
     purposes as having become the record holder or holders of such shares of
     Common Stock at such time; provided, however, that any such surrender
     (other than for provisional conversion) on any date when the stock transfer
     books of the Corporation are closed shall be deemed to have been made, and
     shall be effective to terminate the rights of the holder or holders of the
     shares of Series A Preferred so surrendered for conversion and to
     constitute the person or persons entitled to receive such shares of Common
     Stock as the record holder or holders thereof for all purposes, at the
     opening of business on the next succeeding day on which such transfer books
     are open and such conversion shall be at the Conversion Price in effect at
     such time. If shares are surrendered for provisional conversion, the
     Corporation shall either (i) reissue certificates for the number of shares
     of Series A Preferred surrendered for provisional conversion, if the sale
     of the underlying Common Stock (as provided in Section 9(a) above) does not
     occur, or (ii) issue certificates for the number of shares of Common Stock
     into which the shares provisionally surrendered have been converted to the
     order of the purchaser thereof, if the sale of the underlying Common Stock
     (as provided in Section 9(a) above) does occur. If, following the delivery
     of a notice of redemption by the Corporation pursuant to Section 6 hereof,
     but not otherwise, a holder of shares of Series A Preferred elects to
     exercise its rights of conversion under this Section 9, such holders of
     shares of Series A Preferred who surrender their shares of Series A
     Preferred for conversion shall be entitled to payment in cash by the
     Corporation of all accrued and unpaid dividends to the date the Series A
     Preferred are surrendered for conversion (or deemed to have been converted,
     in the case of shares provisionally converted), prorated for any portion of
     the then current dividend period during which the Series A Preferred are
     surrendered for conversion, whether or not any dividend in respect of the
     then-current dividend period has been declared or set aside. The
     Corporation shall make that payment as promptly as practicable following
     the surrender of certificates for shares of Series A Preferred for
     conversion as provided herein (or following the sale of the underlying
     Common Stock, in the case of shares that are provisionally converted and
     subsequently sold as provided in Section 9(a) hereof) and, when applicable,
     shall accompany the certificates for Common Stock into which such shares of
     Series A Preferred have been converted.

          (d) Before taking any action which would cause an adjustment reducing
     the Conversion Price below the then par value of the shares of Common Stock
     deliverable upon conversion of the shares of Series A Preferred, the
     Corporation will take any corporate action which may, in the opinion of its
     counsel, be necessary in order that the Corporation may validly and legally
     issue fully paid and non-assessable shares of Common Stock at such adjusted
     Conversion Price.

                                      -11-
<PAGE>   12

          (e) The Conversion Price shall be subject to adjustment from time to
     time as follows:

               (i) In case at any time the Corporation shall (A) subdivide the
          outstanding shares of Common Stock into a greater number of shares, or
          (B) combine the outstanding shares of Common Stock into a smaller
          number of shares, the Conversion Price in effect immediately prior
          thereto shall be adjusted proportionately so that the adjusted
          Conversion Price shall bear the same relation to the Conversion Price
          in effect immediately prior to such event as the total number of
          shares of Common Stock outstanding immediately prior to such event
          shall bear to the total number of shares of Common Stock outstanding
          immediately after such event. Such adjustment shall become effective
          immediately after the effective date of a subdivision or combination.

               (ii) In case at any time the Corporation shall declare, order,
          pay or make any dividend or other distribution to holders of the
          Common Stock payable in shares of Common Stock, then, in each such
          case, subject to Section 9(e)(v) hereof, the Conversion Price in
          effect immediately prior to the close of business on the record date
          fixed for determination of holders of any class of securities entitled
          to receive such dividend or distribution shall be reduced to a price
          (calculated to the nearest .001 of a cent) determined by multiplying
          such Conversion Price by a fraction:

                    (A) the numerator of which shall be the number of shares of
               Common Stock outstanding immediately prior to such dividend or
               distribution; and

                    (B) the denominator of which shall be the number of shares
               of Common Stock outstanding immediately after such dividend or
               distribution.

          Shares of Common Stock owned by or held for the account of the
          Corporation shall not be deemed outstanding for the purpose of any
          such computation. Such adjustment shall be made on the date such
          dividend is paid or such distribution is made and shall become
          effective retroactive to the record date for the determination of
          stockholders entitled to receive such dividend or distribution.

               (iii) In case at any time the Corporation shall declare, order,
          pay or make any dividend or other distribution to all holders of the
          Common Stock, other than a dividend payable in shares of Common Stock
          (including, without limitation, dividends or distributions payable in
          cash, evidences of indebtedness, rights, options or warrants to
          subscribe or purchase any Common Stock or other securities, or any
          other securities or other property, but excluding any rights to
          purchase any stock or other securities if such rights are not
          separable from the Common Stock except upon the occurrence of a
          contingency beyond the control of the Corporation), then, and in

                                      -12-
<PAGE>   13
          each such case, subject to Section 9(e)(v) hereof, the Conversion
          Price in effect immediately prior to the close of business on the
          record date fixed for the determination of holders of Common Stock
          entitled to receive such dividend or distribution shall be reduced to
          a price (calculated to the nearest .001 of a cent) determined by
          multiplying such Conversion Price by a fraction:

                    (A) the numerator of which shall be the Market Price per
               share of Common Stock in effect as of such record date or, if the
               Common Stock trades on an ex-dividend basis, on the Trading Day
               immediately prior to the date of commencement of ex-dividend
               trading, less the value of such dividend or distribution (as
               determined in good faith by the Board of Directors of the
               Corporation) applicable to one share of Common Stock; and

                    (B) the denominator of which shall be such Market Price per
               share of Common Stock as of such record date or, if the Capital
               Stock trades on an ex-dividend basis, on the Trading Day
               immediately prior to the date of commencement of ex-dividend
               trading.

          Such adjustment shall be made on the date such dividend is paid or
          such distribution is made and shall become effective retroactive to
          the record date for the determination of stockholders entitled to
          receive such dividend or distribution. In case at any time the
          Corporation shall declare, order, pay or make a dividend or rights to
          purchase any stock or other securities that are not separable from the
          Common Stock except upon the occurrence of a contingency beyond the
          control of the Corporation, the Corporation shall make provision so
          that the holder of any share of Series A Preferred thereafter
          surrendered for conversion shall be entitled to receive the number of
          shares of Common Stock and rights to purchase stock or other
          securities that such holder would have owned or have been entitled to
          receive after the occurrence of any of such events had the share of
          Series A Preferred been surrendered for conversion immediately before
          the occurrence of such event or the record date therefor, whichever is
          earlier. If any such rights are redeemed, the holder of Series A
          Preferred shall have the right to receive, in lieu of any such rights,
          any cash, property or securities paid in respect of such redemption.

               (iv) In case at any time the Corporation issues or sells any
          shares of Common Stock or any rights, options or warrants to subscribe
          for or purchase shares of Common Stock or shares having the same
          rights, privileges and preferences as the Common Stock ("EQUIVALENT
          COMMON STOCK") or securities convertible into Common Stock or
          equivalent common stock, at a price per share of Common Stock or
          equivalent common stock (or having a conversion price per share, if a
          security is convertible into shares of Common Stock or equivalent
          common stock) less than the Market Price of the Common Stock as of the
          date of such issue or sale, then upon such issue or sale the
          Conversion Price shall be reduced to such Conversion Price

                                      -13-
<PAGE>   14
          determined by multiplying the Conversion Price in effect immediately
          prior to such issue or sale by a fraction, (y) the numerator of which
          shall be the sum of the number of shares of Common Stock outstanding
          immediately prior to such issue or sale plus the number of shares of
          Common Stock which the aggregate offering price of the total number of
          shares of Common Stock and/or equivalent common stock so to be offered
          (and/or the aggregate initial conversion price of the convertible
          securities so to be offered) would purchase at such Market Price and
          (z) the denominator of which shall be the sum of the number of shares
          of Common Stock outstanding immediately prior to such issue or sale
          plus the number of additional shares of Common Stock and/or equivalent
          common stock to be offered for subscription or purchase (or into which
          the convertible securities so to be offered are initially
          convertible). In case such subscription price may be paid in a
          consideration part of or all of which shall be in a form other than
          cash, the value of such consideration shall be determined in good
          faith by the Board of Directors of the Corporation. Shares of Common
          Stock owned by or held for the account of the Corporation shall not be
          deemed outstanding for the purpose of any such computation. Such issue
          or sale adjustment shall be made successively upon the issuance or
          sale of shares of Common Stock or equivalent common stock or any
          rights, options or warrants to subscribe for or purchase Common Stock
          or equivalent common stock or securities convertible into common stock
          or equivalent common stock. Notwithstanding the foregoing, no
          adjustment of the Conversion Price pursuant to this Section 9(e)(iv)
          shall be made upon (A) the conversion or redemption of shares of
          Series A Preferred; (B) the payment of any stock dividend on the
          Series A Preferred; (C) the issuance of options to officers, directors
          and employees of the Corporation and its subsidiaries to purchase
          shares of Common Stock, including any such options as are issued and
          outstanding as of the Original Issue Date, provided that, with respect
          to all such options, the number of shares of Common Stock that may be
          subject to such options shall be limited to 15% of the Corporation's
          fully diluted shares of Common Stock based upon securities outstanding
          as of the Original Issue Date; (D) the issuance and sale of Common
          Stock upon exercise of any rights or options referenced in the
          immediately preceding clause (C) or in Section 9(e)(iii) above; or (E)
          the issuance and sale of Common Stock in an underwritten public
          offering.

               (v) If the amount of any adjustment of the Conversion Price
          required pursuant to this Section 9(e) would be less than 1% of the
          Conversion Price in effect at the time such adjustment is otherwise so
          required to be made, such amount shall be carried forward and an
          adjustment with respect thereto made at the time of and together with
          any subsequent adjustment which, together with such amount and any
          other amount or amounts so carried forward, shall aggregate at least
          1% of such Conversion Price. All calculations under this Section 9(e)
          shall be made to the nearest .001 of a cent.

               (vi) Except as herein otherwise expressly provided, for all
          purposes of this

                                      -14-
<PAGE>   15
               Section 9(e) the term "Common Stock" shall mean the Common Stock
               and any shares of stock or other class of capital stock of the
               Corporation which is not preferred as to dividends or assets over
               any other class of capital stock of the Corporation and which is
               not subject to redemption, or which is issued to the holders of
               shares of Common Stock upon any reclassification thereof.

          Notwithstanding anything in this Section 9(e), there will be no
          adjustment hereunder as a result of the reverse stock split
          contemplated in Section 5.17 of the Agreement and Plan of Merger dated
          October 8, 1999, to which the Corporation is a party, which reverse
          stock split shall be deemed to have occurred prior to effectiveness of
          this Certificate.

               (f) In case at any time after the Original Issue Date, the
          Corporation shall be a party to any transaction (including without
          limitation a merger, consolidation, statutory share exchange, sale of
          all or substantially all of the Corporation's assets or
          recapitalization of the Common Stock), in each case as a result of
          which shares of Common Stock (or any other securities of the
          Corporation then issuable upon conversion of the Series A Preferred)
          shall be converted into the right to receive stock, securities or
          other property (including without limitation cash or any combination
          thereof) (each of the foregoing transactions being referred to as a
          "FUNDAMENTAL CHANGE TRANSACTION"), then the shares of Series A
          Preferred remaining outstanding will thereafter no longer be subject
          to conversion into Common Stock (or such other securities) pursuant to
          this Section 9, but instead each share shall be convertible into the
          kind and amount of stock and other securities and property receivable
          (including without limitation cash) upon the consummation of such
          Fundamental Change Transaction by a holder of that number of shares or
          fraction thereof of Common Stock (or such other securities) into which
          one share of Series A Preferred was convertible immediately prior to
          such Fundamental Change Transaction assuming such holder of Common
          Stock failed to exercise any right of election as to the kind of
          consideration to be received in such Fundamental Change Transaction.
          The Corporation shall not be a party to any Fundamental Change
          Transaction after which shares of the Series A Preferred shall remain
          outstanding unless the terms of such Fundamental Change Transaction
          are consistent with the provisions of this Section 9(f), and it shall
          not consent or agree to the occurrence of any such Fundamental Change
          Transaction until the Corporation has entered into an agreement with
          the successor or purchasing entity, as the case may be, for the
          benefit of the holders of the shares of Series A Preferred which will
          contain provisions enabling the holders of shares of the Series A
          Preferred which remain outstanding after such Fundamental Change
          Transaction to convert such shares into the consideration received by
          holders of Common Stock (or any other securities of the Corporation
          then issuable upon conversion of the Series A Preferred) at the
          Conversion Price immediately after such Fundamental Change
          Transaction. In the event that at any time, as a result of an
          adjustment made pursuant to this Section 9, the Series A Preferred
          shall become subject to conversion into any securities other than
          shares of Common Stock, thereafter the number of such other securities
          so issuable upon conversion of the shares of Series A Preferred shall
          be subject to adjustment from time to time in a manner and on terms as
          nearly equivalent as practicable to the provisions with

                                      -15-
<PAGE>   16

          respect to the shares of Series A Preferred contained in this Section
          9. The provisions of this Section 9(f) shall similarly apply to
          successive Fundamental Change Transactions.

               (g) Upon the occurrence of any event requiring an adjustment of
          the Conversion Price, then, and in any such case, the Corporation
          shall promptly deliver to the holders of shares of Series A Preferred
          a notice stating the Conversion Price resulting from such adjustment
          and the method of calculation thereof and setting forth a brief
          statement of the facts requiring such adjustment and upon which such
          adjustment is based.

               (h) In case at any time:

                    (i) the Corporation shall declare or pay to all holders of
               Common Stock any dividend (whether payable in Common Stock, cash,
               securities or other property);

                    (ii) there shall be any capital reorganization, or
               reclassification of the Common Stock of the Corporation or
               consolidation or merger of the Corporation with, or sale of all
               or substantially all of its assets to, another corporation or
               other entity;

                    (iii) there shall be a voluntary or involuntary dissolution,
               liquidation or winding-up of the Corporation;

                    (iv) there shall be any other Fundamental Change
               Transaction; or

                    (v) there shall occur any other event that would cause an
               adjustment to the Conversion Price of the Series A Preferred;

          then, in any one or more of such cases, the Corporation shall give to
          the holder of shares of Series A Preferred (A) at least 15 days prior
          to any event referred to in clause (i) or (v) above and at least 30
          days prior to any event referred to in clause (ii), (iii) or (iv)
          above, written notice of the date on which the books of the
          Corporation shall close or records shall be taken for such dividend or
          distribution or for determining rights to vote in respect of any such
          organization, reclassification, consolidation, merger, sale,
          dissolution, liquidation, winding-up or Fundamental Change
          Transaction, and (B) in the case of any such reorganization,
          reclassification, consolidation, merger, sale, dissolution,
          liquidation, winding-up or Fundamental Change Transaction known to the
          Corporation, at least 30 days prior written notice of the date, or if
          not then known, a reasonable approximation thereof by the Corporation)
          when the same shall take place. Such notice in accordance with the
          foregoing clause (A) shall also specify, in the case of any such
          dividend or distribution, the date on which such holders of Common
          Stock shall be entitled thereto, and such notice in accordance with
          the foregoing clause (B) shall also specify the date on which such
          holders of Common Stock shall be entitled to exchange their Common
          Stock, securities or other property deliverable upon such
          reorganization, reclassification, consolidation, merger, sale,

                                      -16-
<PAGE>   17

          dissolution, liquidation, winding-up or Fundamental Change
          Transaction, as the case may be.

               (i) Whenever the Conversion Price is adjusted as provided herein,
          the Corporation shall prepare and mail to the record holders of Series
          A Preferred an officer's certificate signed by the Chairman of the
          Board, President, or Chief Financial Officer of the Corporation
          setting forth the Conversion Price after the adjustment, the method of
          calculation thereof, and a brief statement of the facts requiring the
          adjustment and upon which the adjustment is based. If the calculation
          of the adjustment requires a determination by the Corporations' Board
          of Directors, the certificate shall attach and certify to the
          resolution of the Board of Directors relating to the determination.

               (j) All shares of Common Stock issuable upon the conversion set
          forth in this Section 9 shall be duly authorized, validly issued,
          fully-paid and nonassessable.

     SECTION 10. RANKING. Without limiting the definition of Junior Securities,
the following securities and obligations of the Corporation shall rank junior to
the Series A Preferred with respect to the payments required or permitted to be
made to the holders thereof pursuant to their respective governing instruments
and payments required to be made to the holders of the Series A Preferred
pursuant hereto: the shares of Common Stock. No Senior Securities or Parity
Securities are outstanding or authorized on the date hereof or will be
outstanding or authorized on the Original Issue Date.

     SECTION 11. RECORD HOLDERS. The Corporation may deem and treat the record
holder of any shares of Series A Preferred as the true and lawful owner thereof
for all purposes, and the Corporation shall not be affected by any notice to the
contrary.

     SECTION 12. NOTICES. Except as may otherwise be provided by law or provided
for herein, all notices referred to herein shall be in writing, and all notices
hereunder shall be deemed to have been given upon receipt, in the case of a
notice of conversion given to the Corporation as contemplated in Section 9(b)
hereof, or, in all other cases, upon the earlier of receipt of such notice or
three Business Days after the mailing of such notices sent by first-class mail,
postage prepaid, addressed: If to the Corporation, to its principal executive
offices (Attention: Corporate Secretary) or to any agent of the Corporation
designated as permitted hereby; or if to a holder of the Series A Preferred, to
such holder at the address of such holder as listed in the stock record books of
the Corporation (which shall include the records of the Transfer Agent), or to
such other address as the Corporation or holder, as the case may be, shall have
designated by notice similarly given.

     SECTION 13. REGISTRATION OF TRANSFER. Upon the surrender of any certificate
representing the Series A Preferred to the Corporation or its transfer agent,
the Corporation shall, or shall cause its transfer agent to, at the request of
the record holder of such certificate, execute and deliver (at the Corporation's
expense) a new certificate or certificates in exchange therefor, of Series A
Preferred representing in the aggregate the number of shares of Series A
Preferred represented by the

                                      -17-
<PAGE>   18
surrendered certificate. Each such new certificate shall be registered in such
name and shall represent such number of shares of Series A Preferred as is
requested by the holder of the surrendered certificate and shall be
substantially identical in form to the surrendered certificate, and dividends
shall accrue on the Series A Preferred represented by such new certificate from
the date as of which dividends have been fully paid on the Series A Preferred
represented by the surrendered certificate.

     SECTION 14. REPLACEMENT. Upon receipt of evidence satisfactory to the
Corporation (an affidavit of the registered holder shall be satisfactory) of the
ownership and the loss, theft, destruction or mutilation of any certificate
evidencing shares of Series A Preferred, and, in the case of any such loss,
theft or destruction, upon receipt of indemnity reasonably satisfactory to the
Corporation (provided, that, if the holder is a financial institution or other
institutional investor, its own agreement shall be satisfactory), or, in the
case of any such mutilation, upon surrender of such certificate, the Corporation
shall (at its own expense) execute and deliver in lieu of such certificate a new
certificate of like kind representing the number of shares of Series A Preferred
of such class represented by such lost, stolen, destroyed or mutilated
certificate and dated the date of the lost, stolen, destroyed or mutilated
certificate, and dividends shall accrue on the Series A Preferred represented by
such new certificate from the date to which dividends have been fully paid on
the Series A Preferred represented by the lost, stolen, destroyed or mutilated
certificate.

     SECTION 15. SUCCESSORS AND TRANSFEREES. The provisions applicable to shares
of Series A Preferred shall bind and inure to the benefit of and be enforceable
by the Corporation, the respective successors to the Corporation, and by any
record holder of shares of Series A Preferred.

     IN WITNESS WHEREOF, the Corporation has caused this Certificate to be
executed as of the 8th day of February, 2000.

                              VISTA ENERGY RESOURCES, INC.

                              By:/s/ C. Randall Hill
                                 --------------------------
                                 C. Randall Hill
                                 Chairman and Chief Executive Officer

                                      -18-

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