<PAGE>

                                                                    EXHIBIT 10.8

                                   AROC INC.

              AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT

     This Amended and Restated Registration Rights Agreement dated as of April
30, 2000 (this "Agreement"),between AROC Inc., a Delaware corporation formerly
known as American Rivers Oil Company ("AROC"), Bank of America, N.A., a national
association (the "Bank") and LaSalle Street Natural Resources Corporation, a
Delaware corporation and indirect subsidiary of the Bank ("LaSalle")(the Bank
and LaSalle are referred to collectively as the "Investor").

     A.   AROC and LaSalle are parties to two separate Warrant Agreements dated
as of October 13, 1999, (as modified and supplemented and in effect from time to
time, the "Warrant Agreements"), providing for the issuance by AROC of Warrants
(as hereinafter defined) which entitle the Investor to purchase from AROC an
aggregate of 5,679,519 shares of the common stock, par value $0.001 per share
(the "Common Stock") of AROC, as provided in the Warrant Agreement and the
Warrants.

     B.   LaSalle also owns directly an additional 1,500,000 shares of the
Common Stock, and the Company and the Bank are parties to an agreement pursuant
to which the Company has agreed to issue to the Bank shares of Series A
Convertible Preferred Stock, par value $0.001 per share, including shares
issuable as dividends on the outstanding shares (the "Preferred Stock").

     C.   The Company and LaSalle are parties to that certain Registration
Rights Agreement dated as of October 13, 1999, providing for the registration of
the Common Stock of the Company held by LaSalle.

     D.   As partial consideration for the benefits to be derived by the Company
from the various agreements relating to the issuance of the Preferred Stock, the
Company has agreed to amend and restate the October 13, 1999 registration rights
agreement to provide for the registration of the Common Stock issuable upon
conversion of the Preferred Stock to be held by the Bank.

     Accordingly, the parties hereto agree as follows:

Section 1.  Definitions.

     Each capitalized term used herein without definition shall have the meaning
ascribed thereto in the Warrant Agreements.  As used in this Agreement the
following terms have the following meanings:

     "AROC" shall have the meaning set forth in the preamble of this Agreement.

     "Bank" shall have the meaning set forth in the preamble of this Agreement.

     "Benton Holders" means F. Fox Benton, Jr., Lizinka M. Benton, F. Fox Benton
III, Lizinka C. Benton and Lucia T. Benton, in their capacities as "Selling
Shareholders" as that term is defined in that certain Registration Rights
Agreement, dated as of the October 13, 1999, by and among the preceding parties
and AROC.

     "Commission" means the U.S. Securities and Exchange Commission (or any
successor or similar governmental agency or authority) administering the
Securities Act and/or the Exchange Act.

     "Common Stock" means the common stock, par value $0.001 per share, of AROC.
<PAGE>

     "Cutback Registration" means any registration in which the Managing
Underwriter advises AROC, and AROC in turn notifies the holders of Registrable
Securities requested to be included therein in accordance with Section 5.02,
that marketing factors require a limitation of the number of shares of Common
Stock to be underwritten in such registration.

     "Effective Period" has the meaning set forth in Section 5.01(b).

     "Electing Holders" means any Benton Holders or EnCap Holders who have
requested inclusion of shares of Common Stock held by such holder in a
registration.

     "EnCap Holders" means EnCap Investments L.C., EnCap Equity 1996 Limited
Partnership, EnCap Equity 1994 Limited Partnership, Energy Capital Investment
Company PLC, Shahara Oil, L.L.C., Picosa Creek Limited Partnership, EF-II
Holdings, LLC and El Paso Capital Investments, L.L.C., in their capacities as
"Shareholders" as that term is defined in that certain Amended and Restated
Registration Rights Agreement, dated as of April 30, 2000, by and among the
preceding parties and AROC.

     "Exchange Act" means the U.S. Securities Exchange Act of 1934, as amended,
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.

     "Indemnified Party" has the meaning set forth in Section 6.03.

     "Indemnifying Party" has the meaning set forth in Section 6.03.

     "Investor" shall have the meaning set forth in the preamble of this
Agreement.

     "LaSalle" shall have the meaning set forth in the preamble of this
Agreement.

     "Long-Form Requested Registration" shall mean any Requested Registration
that is a registration on a Form S-1 under the Securities Act or any successor
form or similar long-form registration.

     "Managing Underwriter" means, with respect to any registration, the
underwriter or underwriters managing such registration.

     "NASDAQ" has the meaning set forth in Section 12.

     "Original Requesting Holder" has the meaning set forth in Section 3.01(a).

     "Other Requesting Holder" has the meaning set forth in Section 3.01(a).

     "Person" means any individual, corporation, association, joint venture,
limited liability company, partnership, trust, business or other entity or
organization, and shall include any government or political subdivision, or any
agency or instrumentality thereof.

     "Piggyback Registration" means any registration which is not a Requested
Registration, other than (a) any registration on a Form S-8 under the Securities
Act (or any successor thereto); (b) any registration relating to an offering to
be made solely to employees (including management or employee incentive plans);
or (c) any registration on a Form S-4 (or any successor thereto or other
comparable form).

                                       2
<PAGE>

     "Preferred Stock" shall have the meaning set forth in the preamble of this
Agreement.

     "Public Offering" means any offering of Common Stock to the public, either
on behalf of AROC or any of its Stockholders, pursuant to an effective
registration statement under the Securities Act.

     "register," "registered" and "registration" refer to a registration of
Common Stock or other securities of AROC effected by preparing and filing a
registration statement in compliance with the Securities Act and the declaration
or ordering of the effectiveness of such registration statement.

     "Registrable Securities" means (i) shares of Common Stock issued or
issuable upon exercise of any Warrants, including without limitation any Common
Stock into which such Common Stock may thereafter be changed or converted, (ii)
the 1,500,000 shares of Common Stock owned by the Investor at the date of this
Agreement, (iii) shares of Common Stock issued or issuable upon conversion of
any Preferred Stock, and (iv) any additional shares of Common Stock or other
securities issued or distributed by way of a dividend, stock split or other
distribution in respect of the Common Stock referred to in clauses (i), (ii) and
(iii) above, or acquired by way of any rights offering or similar offering made
in respect of the Common Stock referred to in clauses (i), (ii) and (iii) above;
provided, however, that, as to any such shares of Common Stock so issued or
issuable, such shares will cease to be Registrable Securities when such shares
have been sold to the public pursuant to a registration or pursuant to Rule 144.

     "Registration Agreements" means the Agreements described in Exhibit A
hereto.

     "Requested Registration" means a registration requested by holders of
Registrable Securities pursuant to Section 3.

     "Requesting Holder" means any of the original Requesting Holder and the
other Requesting Holders.

     "Rule 144" means Rule 144 promulgated by the Commission under the
Securities Act (or any successor or similar rule then in force).

     "Rule 144A" means Rule 144A promulgated by the Commission under the
Securities Act (or any successor or similar rule then in force).

     "Securities Act" means the U.S. Securities Act of 1933, as amended, 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.

     "Short-Form Registration" means a registration of the Common Stock of AROC
on Form S-2 or Form S-3 under the Securities Act or any successor form or
similar short-form registration.

     "Warrant Agreements" has the meaning set forth in the preamble of this
Agreement.

     "Warrants" has the meaning set forth in the Warrant Agreements.

     "Withdrawing Holder" has the meaning set forth in Section 3.02.

                                       3
<PAGE>

Section 2. Piggyback Registration. If at any time or from time to time after the
date hereof AROC proposes to effect a Piggyback Registration for its account or
for the account of a security holder or holders (other than holders of
Registrable Securities), then AROC shall:

     (a)  promptly give to each holder of Registrable Securities notice thereof
(which notice shall include a list of the jurisdictions in which AROC intends to
attempt to qualify such securities under or otherwise comply with the applicable
blue sky or other state securities laws); and

     (b)  include in such Piggyback Registration (and any related qualification
under or other compliance with blue sky or other state securities laws), and in
any underwriting involved therein, all the Registrable Securities specified in a
request, made within 15 days after receipt of such notice from AROC, by any
holder of Registrable Securities; provided, however, that AROC shall not be
required to include any securities of holders of Registrable Securities in such
registration unless such holders accept the terms of the underwriting as agreed
upon between AROC and the underwriters selected by it; and provided, further,
that if such Piggyback Registration is a Cutback Registration, then the number
of shares of Common Stock to be included in the underwriting or registration
shall be allocated first to AROC, the holders of Registrable Securities and the
Electing Holders (pro rata, based on the total number of shares of securities of
AROC, including Registrable Securities, requested by AROC and each such holder
to be included therein); and thereafter to any other holders requesting
inclusion in the registration on the basis of the number of shares each other
requesting holder requests be included bears to the total number of shares of
all other holders of Common Stock that have been requested be included in such
registration. If a person who has requested inclusion in such registration as
provided above does not agree to the terms of any such underwriting, such person
shall be excluded therefrom by written notice from AROC, the underwriter, or the
holders of Registrable Securities. The securities so excluded shall also be
withdrawn from registration.

     (c)  (i) If, at any time after giving written notice of its intention to
register any of its Common Stock and before the effective date of the
registration statement filed in connection with the registration, AROC
determines for any reason not to register its Common Stock, AROC may, at its
election, give written notice of its determination to the holders of Registrable
Securities and the Electing Holders and, thereupon, shall be relieved of its
obligation to register any Registrable Securities in connection with that
registration, without prejudice, however, to the future rights of the holders of
Registrable Securities under this Section, (ii) if AROC determines in its
discretion to delay the registration of its Common Stock, AROC shall be
permitted to delay the registration of any Registrable Securities for the same
period as the delay in registering any other Common Stock, and (iii) AROC is not
required to effect any registration for a requesting holder of Registrable
Securities pursuant to this Section 2 unless it receives reasonable assurances
that the requesting holder of Registrable Securities will pay any expenses
required to be paid by it as a provided in Section 5.

     (d)  The rights of holders with respect to Piggyback Registrations shall be
pari passu with the piggyback registration rights of Benton Holders and the
EnCap Holders.

Section 3. Requested Registration.

3.01. Request for Registration.

     (a)  If after the date AROC shall receive a request from any holder of
Registrable Securities (including Warrants) that AROC effect any registration
under the Securities Act to which such holder is entitled under this Section 3
(including without limitation any related qualification under or compliance with
blue sky or other state securities laws) with respect to all or a part of the
Registrable Securities

                                       4
<PAGE>

owned by such holder, then AROC shall promptly give notice of such request to
each other holder of Registrable Securities, and AROC shall thereupon promptly
use its best efforts diligently to effect such Requested Registration and
related qualifications and compliances within 120 days after receiving such
request for registration (including without limitation the execution of an
undertaking to file post- effective amendments and appropriate qualifications
under or other compliance with the applicable blue sky or other state securities
laws) as may be reasonably requested by the holder of Registrable Securities who
made the original request (the "Original Requesting Holder") and by the holders
of Registrable Securities who make requests to AROC within 15 days after the
giving of the aforesaid notice by AROC (each of the foregoing an "Other
Requesting Holder") and as would permit or facilitate the sale and distribution
of all or such portion of the Registrable Securities as are specified in any
such request; provided, however, that AROC shall not be obligated to take any
action to effect a Requested Registration or any related qualification or
compliance pursuant to this Section 3:

          (i)   if the Requesting Holders do not request to include in such
registration Registrable Securities (issued or issuable on exercise of the
Warrants) having an aggregate Current Adjustment Price (as defined in the
Warrants), determined as of the date of the notice from the Original Requesting
Holder under Section 3.01(a) of (A) at least $750,000 for the holders' first
Requested Registration or (B) at least $250,000 for the holders' second
Requested Registration;

          (ii)  if AROC shall have already effected two Requested Registrations
on behalf of the holders of Registrable Securities pursuant to this Section
3.01, each of which Requested Registrations (A) has been declared or ordered
effective (including without limitation qualification under or other compliance
with state blue sky or securities laws requested) and which effectiveness has
not been suspended or stopped by any governmental or judicial authority, and (B)
remains continuously effective for a period of time not less than the Effective
Period; or

          (iii) if, within 30 days after receipt of the initial request of the
Original Requesting Holder pursuant to this Section 3.01, AROC shall elect to
include in such registration Common Stock for its own account, whereupon AROC
shall notify each Requesting Holder that AROC has elected to effect a Piggyback
Registration and shall thereafter diligently proceed to do so, including therein
the Registrable Securities as to which notice was given by the Requesting
Holders pursuant to this Section 3.01, but subject to the limitations set forth
in Section 2(b)(i) (it being understood, however, that such registration shall
not be deemed to be a Requested Registration for the purposes of Sections
3.01(a)(ii) or 3.01(c)).

          (iv)  Notwithstanding the foregoing, (A) AROC shall not be obligated
to effect a registration pursuant to this Section 3 during the period starting
with the date 60 days prior to AROC's good faith estimated date of filing of,
and ending on a date 120 days following the effective date of, a registration
statement pertaining to an underwritten public offering of securities for the
account of AROC, provided that AROC is at all times during such period
diligently pursuing such registration, (B) AROC shall not be obligated to effect
a registration of Registrable Securities pursuant to this Section 3 pursuant to
any request of Holders of Registrable Securities if such request is received
after the receipt by AROC of a request for registration pursuant to one of the
Registration Agreements, and any such registration pursuant to this Section 3
would likely result in a registration statement being declared effective prior
to the date that is 90 days after the effective date of any such registration
effected pursuant to the Registration Agreement, and (C) AROC shall not be
obligated to effect a registration pursuant to this Section 3 and shall have the
right to defer such filing for a period of not more than 120 days after receipt
of the request of holders of Registrable Securities, if AROC shall furnish to
such holders a certificate signed by the President of AROC stating that in the
good faith judgment of the Board of Directors of AROC, it would be seriously
detrimental to AROC and its shareholders for such registration

                                       5
<PAGE>

statement to be filed and it is therefore essential to defer the filing of such
registration statement; provided, however, that, subject to the limitation set
forth in the proviso in Section 3.01(a)(ii), if AROC shall no longer be eligible
to effect a Short-Form Requested Registration following the deferral of
registration pursuant to this paragraph, then the holders of Registrable
Securities shall, subject to Section 3.01(a)(ii), be entitled to a Long-Form
Requested Registration for each such deferral.

          (v)  If at any time after the holders' initial Requested Registration,
a request of the holders of Registrable Securities for a Requested Registration
shall be denied by AROC solely because the aggregate Current Adjustment Price of
such Registrable Securities sought to be included in such registration is below
the requisite dollar amount specified in Section 3.01(a)(i)(B), then at the
election of the holders of a majority of the then outstanding Registrable
Securities, and in exchange for the right of the holders to request a second
Requested Registration under this Section 3, the holders shall be entitled to
convert their Registrable Securities represented by Warrants (having an
aggregate Current Adjustment Price for all holders of not more than $250,000)
pursuant to Section 12 of the Warrant.

     (b)  If a Requested Registration becomes a Cutback Registration and the
number of shares of Registrable Securities actually sold in such Requested
Registration is not at least a majority of the number of shares of Registrable
Securities requested to be included in such registration, then (A) such
Requested Registration shall not be deemed to be a Requested Registration for
the purposes of Section 3.01(a)(ii); and (B) notwithstanding that such Requested
Registration is a Cutback Registration, AROC shall continue to use its best
efforts diligently to comply with all its obligations (including without
limitation payment of expenses) under this Agreement with respect to such
Requested Registration.  The registration statement filed pursuant to the
request of holders of Registrable Securities may, subject to the provisions of
Section 3.01(c), include other shares of Common Stock of AROC, which are held by
persons who, by virtue of agreements with AROC, are entitled to include their
securities in any such registration, and AROC shall have the right to include
shares of Common Stock in such registration for its own account as provided
therein.

     (c)  If a Requested Registration becomes a Cutback Registration, the number
of Common Stock to be included in the underwriting or registration shall be
allocated first to the holders of Registrable Securities and the Electing
Holders (pro rata, based on the number of Registrable Securities requested by
each such holder to be included therein), second to AROC and thereafter to any
other holders requesting inclusion in the registration on the basis of the
number of shares each other requesting holder requests be included bears to the
total number of shares of all other holders of Common Stock that have been
requested be included in such registration. If a person who has requested
inclusion in such registration as provided above does not agree to the terms of
any such underwriting, such person shall be excluded therefrom by written notice
from AROC, the underwriter, or the holders of Registrable Securities. The
securities so excluded shall also be withdrawn from registration.

3.02. Underwriting. If Requesting Holders intend to distribute the Registrable
Securities covered by such request by means of an underwriting, the Requesting
Holders shall so advise AROC as a part of the request made pursuant to this
Section 3, and in such event, the Requesting Holders shall negotiate in good
faith with an underwriter or underwriters proposed by AROC to act as the
Managing Underwriter in connection with the underwriting of the Requested
Registration; provided, however, that if those Requesting Holders who hold at
least a majority of the Registrable Securities to be included in such Requested
Registration have not agreed with such underwriter or underwriters as to the
terms and conditions of such underwriting within 20 days following commencement
of such negotiations, then the Requesting Holders may select an underwriter or
underwriters of their choice to be the Managing Underwriter, which choice shall
be subject to the approval of the Board of Directors of AROC (such approval not
to be unreasonably withheld or delayed, taking into account AROC's agreements
with

                                       6
<PAGE>

underwriters then in effect).AROC and the Requesting Holders shall enter into an
underwriting agreement in customary form with the underwriter or underwriters
selected for such underwriting (it being understood that (i) all expenses
customarily paid for by the issuer of securities pursuant to such an
underwriting agreement shall be paid for by AROC, and (ii) all indemnification
obligations which are customarily those of the issuer of securities under such
underwriting agreement shall be the obligations of AROC).If a Requesting Holder
disapproves of the terms of an underwriting (the "Withdrawing Holder"), the
Withdrawing Holder may elect to withdraw therefrom by notice to AROC and the
Managing underwriter; and each of the remaining Requesting Holders shall be
entitled to increase the number of shares of Registrable Securities being
registered to the extent of the shares withdrawn by the Withdrawing Holder in
the proportion which the number of shares of Registrable Securities being
registered by such remaining Requesting Holder bears to the total number of
shares being registered by all such remaining Requesting Holders; provided,
however, that the requirements contained in Section 3.01(a)(i) shall then be met
and subject to Section 3.01(c).

Section 4. Expenses of Registration.

     Except as otherwise provided herein, (a) in the case of Requested
Registrations pursuant to Section 3, all expenses incurred by AROC or the
Holders in connection with any registration, qualification or compliance
effected pursuant to this Agreement, including without limitation all
registration, filing and qualification fees, printing expenses, fees and
disbursements of counsel for AROC and for the holders of Registrable Securities,
and the expenses of any audits required by such registration, shall be borne by
AROC and (b) in the case of Piggyback Registrations pursuant to Section 2 (other
than a primary registration by AROC), all of the incremental expenses incurred
by AROC (and not otherwise reimbursed) shall be borne by the holders of
Registrable Securities included in any registration pursuant to the terms
hereof; provided, however, that AROC shall not be required to pay: (i) the
underwriters' fees, discounts or commissions relating to Registrable Securities;
or (ii) the fees and disbursements of more than a single law firm for all
holders of Registrable Securities to be selected by the holders of a majority of
such Registrable Securities participating in a Requested Registration pursuant
to Section 3. Notwithstanding the foregoing, AROC shall not be required to pay
for any expenses of any registration proceeding begun pursuant to Section 3 if
the request for registration is subsequently withdrawn at the request of the
holders of a majority of the Registrable Securities to be registered therein
(which holders shall bear such expenses), unless the holders of a majority of
the Registrable Securities agree that such registration shall be deemed to
constitute a Requested Registration for purposes of the limitation set forth in
the proviso of Section 3.01(a)(ii); provided, however, that if (a) between the
date such request for registration is made and the date of such withdrawal,
there has occurred a material adverse change in the condition, business or
prospects of AROC (or a material adverse change occurring prior to such request
is first publicly disclosed) and (b) such withdrawal shall have occurred prior
to the effective date of the applicable registration statement (it being
understood that the holders shall only have the right to withdraw a Requested
Registration prior to such effective date), then the holders shall not be
required to pay any of such expenses and no Requested Registration shall be
deemed to have occurred pursuant to Section 3.

Section 5. Registration Procedures.

5.01. In the case of each registration, qualification or compliance effected by
AROC pursuant to this Agreement, AROC shall, by notice to each holder of
Registrable Securities included in such registration, keep such holder advised
in writing as to the initiation, progress and effective date of each
registration, qualification and compliance, and, at the expense of AROC, AROC
will:

                                       7
<PAGE>

     (a)  prepare and file with the Commission a registration statement with
respect to such Registrable Securities and use its best efforts to cause such
registration statement to become effective as soon as reasonably practicable
thereafter; and before filing a registration statement or prospectus or any
amendments or supplements thereto, furnish to the Investor (provided Registrable
Securities held by the Investor are covered by such registration statement) and
the underwriter or underwriters, if any, copies of all such documents proposed
to be filed, including without limitation documents incorporated by reference in
the prospectus and, if requested by such holders of Registrable Securities, the
exhibits incorporated by reference, and such holders shall have the opportunity
to object to any information pertaining to such holders that is contained
therein and AROC will make the corrections reasonably requested by an
underwriter or such holders with respect to such information prior to filing any
registration statement or amendment thereto or any prospectus or any supplement
thereto;

     (b)  prepare and file with the Commission 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 for a period
(the "Effective Period") of not less than 180 days, or such shorter period as is
necessary to complete the distribution of the securities covered by such
registration statement and comply with the provisions of the Securities Act with
respect to the disposition of all securities covered by such registration
statement during such period in accordance with the intended methods of
disposition by the seller thereof set forth in such registration statement;

     (c)  furnish to each seller of Registrable Securities such number of copies
of such registration statement, each amendment and supplement thereto, the
prospectus included in such registration statement (including without limitation
each preliminary prospectus) and such other documents as such seller may
reasonably request in order to facilitate the disposition of the Registrable
Securities owned by such seller;

     (d)  use its best efforts to register or qualify such Registrable
Securities under such other securities or blue sky laws of such jurisdictions as
any seller reasonably requests and take such other steps which may be necessary
or advisable in the reasonable judgment of the managing underwriter (and at the
reasonable request of such managing underwriter) to enable such seller to
consummate the disposition in such jurisdictions of the Registrable Securities
owned by such seller (provided that AROC will not for any such purpose be
required to (1) qualify generally to do business as a foreign corporation in any
jurisdiction where it would not otherwise be required to qualify but for the
requirements of this subsection; (2) subject itself to taxation in any such
jurisdiction; (3) consent to general service of process in any such
jurisdiction; or (4) register or qualify Registrable Securities or take any
other action under the state securities or "Blue Sky" laws of any jurisdiction
if, in the judgment of the Board of Directors of AROC, the consequences of the
registration, qualification or other action would be unduly burdensome to AROC).

     (e)  notify the Investor and each seller of such Registrable Securities
when a prospectus relating thereto is required to be delivered under the
Securities Act, of the occurrence of any event as a result of which the
prospectus included in such registration statement contains an untrue statement
of a material fact or omits any fact necessary to make the statements therein
not misleading, and, at the request of any such seller, or at the request of any
seller upon the happening of any event of the kind described in Section 5.01(k),
AROC shall prepare a supplement or amendment to such prospectus so that, as
thereafter delivered to the purchasers of such Registrable Securities, such
prospectus shall not contain an untrue statement of a material fact or omit to
state any fact necessary to make the statements therein not misleading or cures
the event of the kind described in Section 5.01(k);

                                       8
<PAGE>

     (f)  in the case of an underwritten offering, cause to be delivered to the
sellers of Registrable Securities and the underwriters, if any, opinions of
counsel to AROC in customary form, covering such matters as are customarily
covered by opinions for an underwritten public offering as the underwriters may
reasonably request and addressed to the underwriters and such sellers;

     (g)  make available for inspection by any seller of Registrable Securities
that is a Significant Holder, any underwriter participating in any disposition
pursuant to such registration statement, and any attorney, accountant or other
agent retained by any seller or underwriter, all financial and other records,
pertinent corporate documents and properties of AROC, and cause AROC's officers,
directors, employees and independent accountants to supply all information
reasonably requested by any such seller, underwriter, attorney, accountant or
agent in connection with such registration statement;

     (h)  provide a transfer agent and registrar for all such Registrable
Securities not later than the effective date of such registration statement;

     (i)  cause to be delivered, immediately prior to the effectiveness of the
registration statement (and, in the case of an underwritten offering, at the
time of delivery of any Registrable Securities sold pursuant thereto), letters
from AROC's independent certified public accountants addressed to each seller
that is a Significant Holder and each underwriter, if any, stating that such
accountants are independent public accountants within the meaning of the
Securities Act and the applicable published rules and regulations thereunder,
and otherwise in customary form and covering such financial and accounting
matters as are customarily covered by letters of the independent certified
public accountants delivered in connection with primary or secondary
underwritten public offerings, as the case may be;

     (j)  make generally available to the holders of Registrable Securities a
consolidated earnings statement (which need not be audited) for the 12 months
beginning after the effective date of a registration statement as soon as
reasonably practicable after the end of such period, which earnings statement
shall satisfy Section 11(a) of the Securities Act and Rule 158 thereunder; and

     (k)  promptly notify the Investor and any Significant Holder selling
Registrable Securities in such registration and the underwriter or underwriters,
if any:

          (i)   when the registration statement, any preeffective amendment, the
prospectus or any prospectus supplement or post-effective amendment to the
registration statement has been filed and, with respect to the registration
statement or any post-effective amendment, when the same has become effective;

          (ii)  of any written request by the Commission for post-effective
amendments or supplements to the registration statement or prospectus;

          (iii) of the notification to AROC by the Commission of its initiation
of any proceeding with respect to the issuance by the Commission of, or the
issuance by the Commission of, any stop order suspending the effectiveness of
the registration statement; and

          (iv)  of the receipt by AROC of any notification with respect to the
suspension of the qualification of any Registrable Securities for sale under the
applicable securities or blue sky laws of any jurisdiction.

5.02. As soon as possible following receipt of notice from the Managing
Underwriter that a particular registration is a Cutback Registration, AROC will
notify the Investor and each of the holders of

                                       9
<PAGE>

Registrable Securities that is a Significant Holder requested to be included
therein that such registration is a Cutback Registration and of the effect
thereof on the ability of such holders to include their shares in such
registration.

5.03. AROC will use its best efforts to become (and thereafter to remain)
eligible to effect Short-Form Registrations.

5.04. Whenever the holders of Registrable Securities have requested that any
Registrable Securities be registered pursuant to Section 2 or Section 3, each
holder of Registrable Securities will be deemed to have agreed that, upon
receipt of any notice from AROC of the happening of any event of the kind
described in Section 5.01(e) or Section 5.01(k)(ii) or (iii), the holders of
Registrable Securities covered by such registration statement will forthwith
discontinue disposition of any such Registrable Securities until the holders of
Registrable Securities receive copies of the supplemented or amended prospectus
contemplated by Section 5.01(e), or until they are advised in writing by AROC
that the use of the applicable prospectus may be resumed, and they have received
copies of any additional or supplemental filings that are incorporated or deemed
to be incorporated by reference in such prospectus (it being the agreement of
the parties hereto, however, that the obligation of AROC with respect to
maintaining the subject registration statement current and effective shall be
extended by a period of days equal to the period the holders of Registrable
Securities are required by this Section 5.04 to discontinue disposition of such
Registrable Securities.

Section 6. Indemnification; Contribution.

6.01. With respect to any registration, qualification or compliance effected or
to be effected pursuant to this Agreement, AROC shall indemnify each holder of
Registrable Securities whose securities are included or are to be included
therein, each such holder's directors, officers, employees, stockholders,
Affiliates and agents, each underwriter (as defined in the Securities Act) of
the securities sold by such holder and each Person who controls (within the
meaning of the Securities Act) any such holder or underwriter, from and against
all claims, losses, damages and liabilities (or actions in respect thereof)
arising out of or based on:

          (i)   any untrue statement (or alleged untrue statement) of a material
fact contained in any prospectus, offering circular or other document (including
without limitation any related registration statement, notification or the
like), or any amendment thereof or supplement thereto, incident to any such
registration, qualification or compliance;

          (ii)  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; or

          (iii) any violation by AROC of the Securities Act, the Exchange Act or
any rule or regulation promulgated thereunder applicable to AROC, or of any blue
sky or other state securities laws or any rule or regulation promulgated
thereunder applicable to AROC,

and will reimburse each such Person entitled to indemnity under this Section
6.01 for all legal and other expenses reasonably incurred, as the same are
incurred, in connection with investigating or defending any such claim, loss,
damage, liability or action; provided, however, that the foregoing indemnity and
reimbursement obligation shall not be applicable to the extent that any such
claim, loss, damage or liability arises out of or is based on any untrue
statement (or alleged untrue statement) or omission (or alleged omission) or
violation made in reliance upon and in conformity with written information
furnished to AROC by such holder specifically for use in such prospectus,
offering circular, other

                                       10
<PAGE>

document, amendment or supplement; and provided further that the foregoing
indemnity and reimbursement obligation shall not be applicable with respect to
any preliminary prospectus to the extent that any loss, claim, damage, liability
or expense of the indemnitee results from the fact that a holder of Registrable
Securities sold Registrable Securities to a person to whom there was not sent or
given, at or prior to the written confirmation of the sale, a copy of the
prospectus (excluding documents incorporated by reference) or of the prospectus
as then amended or supplemented (excluding documents incorporated by reference)
if AROC has previously furnished copies thereof to the holder of Registrable
Securities in compliance with Section 5 of this Agreement and the loss, claim,
damage, liability or expense of the indemnitee results from an untrue statement
or omission of a material fact contained in such preliminary prospectus which
was corrected in the prospectus (or the prospectus as amended or supplemented).

6.02. With respect to any registration, qualification or compliance effected or
to be effected pursuant to this Agreement, each holder of Registrable Securities
which are included or are to be included in such registration, qualification or
compliance shall indemnify AROC, its directors, officers, employees,
stockholders, Affiliates and agents, each underwriter (as defined in the
Securities Act) of the securities of such holder, each Person who controls
(within the meaning of the Securities Act) AROC or any such underwriter from and
against all claims, losses, damages and liabilities (or actions in respect
thereof) arising out of or based on:

     (i)   any untrue statement (or alleged untrue statement) of a material fact
contained in any prospectus, offering circular or other document (including
without limitation any related registration statement, notification or the
like), or any amendment thereof or supplement thereto, incident to any such
registration, qualification or compliance;

     (ii)  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;

     (iii) any violation by such holder of the Securities Act, the Exchange Act
or any rule or regulation promulgated thereunder applicable to such holder, or
of any blue sky or other state securities law or any rule or regulation
promulgated thereunder applicable to such holder, and will reimburse each such
Person entitled to indemnity under this Section 6.02 for any legal and other
expenses reasonably incurred in connection with investigating or defending any
such claim, loss, damage, expense, liability or action; or

     (iv)  with respect to any preliminary prospectus, the fact that any holder
of Registrable Securities sold Registrable Securities to a person to whom there
was not sent or given, at or prior to the written confirmation of the sale, a
copy of the prospectus (excluding documents incorporated by reference) or of the
prospectus as then amended or supplemented (excluding documents incorporated by
reference) if (a) AROC has previously furnished copies thereof to the holder of
Registrable Securities in compliance with Section 5 of this Agreement and (b)
the loss, claim, damage, liability or expense of the indemnitee results from an
untrue statement or omission of a material fact contained in the preliminary
prospectus which was corrected in the prospectus (or the prospectus as amended
or supplemented);

but in each case of the preceding subsections (i), (ii), (iii) and (iv), only to
the extent that such untrue statement (or alleged untrue statement) or omission
(or alleged omission) or violation is made in such prospectus, offering
circular, other document, amendment or supplement in reliance upon and in
conformity with written information furnished to AROC by such holder
specifically for use in such prospectus, offering circular, other document,
amendment or supplement.

                                       11
<PAGE>

6.03. Each Person entitled to indemnification under this Section 6 (an
"Indemnified Party") shall give notice to the party required to provide
indemnification (the "Indemnifying Party") promptly after the Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought, and shall
permit the Indemnifying Party to assume the defense of any such claim or any
litigation resulting therefrom; provided, however, that:

      (i)   counsel for the Indemnifying Party who shall conduct the defense of
any such claim or any litigation shall be approved by the Indemnified Party
(which approval shall not be unreasonably withheld or delayed);

      (ii)  the Indemnified Party may participate in such defense at the
Indemnified Party's expense; provided, however, that the Indemnified Party or
Indemnified Parties shall have the right to employ a single law firm and a
single local counsel law firm to represent it or them if, in the reasonable
judgment of the Indemnified Party or Indemnified Parties, it is advisable for it
or them to be represented by separate counsel by reason of having legal defenses
which are different from or in addition to those available to the Indemnifying
Party, and in that event the reasonable fees and expenses of one such law firm
and one such local law firm shall be paid by the Indemnifying Party; and

      (iii) failure of any Indemnified Party to give notice as provided herein
shall not relieve the Indemnifying Party of its obligations under this Section
6.

      No Indemnifying Party, in the defense of any such claim or litigation,
shall, except with the consent of the Indemnified Party to which such claim or
litigation relates, consent to entry of any judgment or enter into any
settlement unless such settlement relieves the Indemnified Party of any and all
liability.  Each Indemnified Party shall furnish such information regarding
itself for the claim in question as an Indemnifying Party may reasonably request
in writing and as shall be reasonably required in connection with defense of
such claim in litigation resulting therefrom.

6.04. If the indemnity and reimbursement obligation provided for in each of
Section 6.01 and Section 6.02 is unavailable or insufficient to hold harmless an
Indemnified Party in respect of any claims, losses, damages or liabilities (or
actions in respect thereof) referred to therein, then the Indemnifying Party
shall contribute to the amount paid or payable by the Indemnified Party as a
result of such claims, losses, damages or liabilities (or actions in respect
thereof) in such proportion as is appropriate to reflect the relative fault of
the Indemnifying Party, on the one hand, and the Indemnified Party, on the other
hand, in connection with statements or omissions which resulted in such claims,
losses, damages or liabilities, as well as any other relevant equitable
considerations. The relative fault shall be determined by reference to, among
other things, whether the untrue or alleged untrue statement of a material fact
or the omission or alleged omission to state a material fact relates to
information supplied by the Indemnifying Party or the Indemnified Party and the
parties' relative intent, knowledge, access to information and opportunity to
correct or prevent such untrue statement or omission, the parties hereto agree
that it would not be just and equitable if contributions pursuant to this
Section 6.04 were to be determined by pro rata allocation or by any other method
of allocation which does not take account of the equitable considerations
referred to in the first sentence of this Section 6.04. The amount paid by an
Indemnified Party as a result of the losses, claims, damages or liabilities
referred to in the first sentence of this Section 6.04 shall be deemed to
include any legal and other expenses reasonably incurred by such Indemnified
Party in connection with investigating or defending any claim, loss, damage,
liability or action which is the subject of this Section 6.04.

                                       12
<PAGE>

      No Indemnified Party guilty of fraudulent misrepresentation (within the
meaning of Section 11(f) of the Securities Act) shall be entitled to
contribution from the Indemnifying Party if the Indemnifying Party was not
guilty of such fraudulent misrepresentation.

      The provisions of this Section 6 shall be in addition to any other rights
to indemnification or contribution which an indemnified party may have pursuant
to law, equity, contract or otherwise and shall remain in full force and effect
regardless of any investigation made by or on behalf of an Indemnified Party and
shall survive the transfer of the shares of Common Stock or other stock or
securities which may be issued upon exercise of the Warrants.

Section 7. Information by Holders.

      If Registrable Securities owned by a holder are included in any
registration, such holder shall furnish to AROC such information regarding
itself and the distribution proposed by such holder as AROC may reasonably
request and as shall otherwise be required in connection with any registration,
qualification or compliance referred to in this Agreement.

Section 8.  Rule 144 Reporting; Rule 144A Sales.

      With a view to making available to each holder of Registrable Securities
the benefits of certain rules and regulations of the Commission which may permit
the sale of the Registrable Securities to the public without registration, AROC
agrees that until the earlier of (a) the date on which no holder owns any
Registrable Securities or (b) the Expiration Date:

      (a)  AROC shall, at any time after any of AROC's securities are registered
under the Securities Act or the Exchange Act: (i) make and keep available public
information, as those terms are contemplated by Rule 144; (ii) timely file with
the Commission all reports and other documents required to be filed under the
Securities Act and the Exchange Act; (iii) furnish to each holder of Registrable
Securities forthwith upon request a written statement by AROC as to its
compliance with the reporting requirements of the Securities Act and the
Exchange Act, and a copy of the most recent annual or quarterly report of AROC;
and (iv) comply with all rules and regulations of the Commission applicable in
connection with the use of Rule 144 and take such other actions and furnish such
holder with such other public information as such holder may reasonably request
in order to assist such holder in availing itself of any rule or regulation of
the Commission allowing such holder to sell any Registrable Securities without
registration; and

      (b)  each holder of Registrable Securities and each prospective holder of
Registrable Securities who may consider acquiring Registrable Securities in
reliance upon Rule 144A shall have the right to request from AROC, and AROC will
provide upon request, such public information regarding AROC and its business,
assets and properties, if any, as such holder may reasonably request so as to
assist such holder in the transfer of Registrable Securities to such prospective
holder in reliance upon Rule 144A.

Section 9. Other Registration Rights.

9.01. AROC represents and warrants to the Investor that there is not in effect
on the date hereof any agreement by AROC (other than this Agreement and the
other Registration Agreements) pursuant to which any holders of securities of
AROC have a right to cause AROC to register or qualify such securities under the
Securities Act or any applicable state securities laws.  The Investor hereby
consents to AROC entering into the Amended and Restated Registration Rights
Agreement by and among AROC Inc., EnCap Equity 1996 Limited Partnership, EnCap
Equity 1994 Limited Partnership, Energy Capital

                                       13
<PAGE>

Investment Company Plc, Shahara Oil, L.L.C., Picosa Creek Limited Partnership,
EF-II Holdings, LLC and El Paso Capital Investments, L.L.C., dated as of April
30, 2000.

9.02.  So long as any Registrable Securities shall be outstanding, (a) AROC
shall not amend or permit the amendment of the Registration Agreements in any
manner that is inconsistent with this Registration Rights Agreement or which
adversely affect the rights of any holder of Registrable Securities without the
prior written consent of the holders of a majority of the then outstanding
Registrable Securities and (b) AROC shall send any notice in respect of a
registration to be delivered by AROC to any holder of any rights under any of
the Registration Agreements to the Investor and any Significant Holders of
Registrable Securities.so long as any Registrable Securities shall be
outstanding, prior to the Expiration Date (as defined in the Warrant) AROC shall
not agree with the holders of any securities issued or to be issued by AROC to
register or qualify such securities under the Securities Act or any applicable
state securities laws unless such agreement (including any Registration
Agreement) specifically provides that: (a) such holder of such securities may
not participate in any Piggyback Registration except as provided in Section 2;
and (b) the holder of such securities may not participate in any Requested
Registration except as provided in Section 3.

Section 10.  Holdback Agreements. In order to facilitate the possibility of
future public offerings of Common Stock, the holders of Registrable Securities
agree that the Registrable Securities will not be resold during a period
commencing on the filing by AROC of a registration statement under the
Securities Act for an underwritten public offering for cash by AROC of Common
Stock or securities convertible into or exercisable or exchangeable for its
Common Stock and continuing until the earlier of the abandonment of the proposed
public offering or 120 days following the date of the last closing in the public
offering without the consent of the underwriters of such offering, except to the
extent such shares are included in such registration.  Holders of such
Registrable Securities also agree that they will cooperate with AROC in
providing reasonable written assurances respecting the foregoing to the
underwriter of any such public offering.  Holders agree that during the above
restricted period they will not directly or indirectly sell, offer to sell,
contract to sell (including without limitation any short sale), grant an option
to purchase or otherwise transfer or dispose of (other than to donees who agree
to be similarly bound) shares of Registrable Securities at any time during such
period except securities included in such registration.  In order to enforce the
foregoing covenant, AROC may impose stop-order instructions with respect to such
shares of Registrable Securities held by each holder, which shall be binding
upon any assignee or successor of such holder (and the shares or securities of
every other person subject to the foregoing restriction), until the end of the
restricted period.

Section 11.  Miscellaneous.

11.01. Successors and Assigns.  Subject to the provisions of Section 13, this
Agreement shall inure to the benefit of and shall be binding upon the parties
hereto, all the holders of Registrable Securities and their respective legal
representatives, successors and assigns.

11.02. Severability.  If any term or provision of this Agreement, or the
application thereof to any Person or circumstance, shall, to any extent, be
invalid or unenforceable, the remaining terms and provisions of this Agreement
or application to Persons and circumstances shall not be invalidated thereby,
and each term and provision hereof shall be construed with all other remaining
terms and provisions hereof to effect the intent of the parties hereto to the
fullest extent permitted by law.

11.03. Notices. All notices, requests, demands and other communications provided
for hereunder shall be in writing and mailed (by first class registered or
certified mail, postage prepaid), sent by express

                                       14
<PAGE>

overnight courier service or electronic facsimile transmission with a copy by
mail, or delivered to the applicable party at the addresses indicated below:

     If to the Company:

                    AROC Inc.
                    4200 East Skelly Drive, Suite 1000
                    Tulsa, Oklahoma 74135
                    Attention: John A. Keenan
                    Facsimile: 918-494-4918

     With a copy (which shall not constitute notice) to:

                    Jenkens & Gilchrist, a professional corporation
                    1445 Ross Avenue, Suite 3200
                    Dallas, Texas 75202
                    Attention: W. Alan Kailer
                    Facsimile: 214-855-4300

     If to the Investor:

                    Bank of America, N.A.
                    901 Main Street, 64th Floor
                    Dallas, Texas  75202
                    Attn: Marcia Bateman
                    Facsimile: 214-209-9342

     With a copy (which shall not constitute notice) to:

                    Billy Young
                    Vinson & Elkins LLP
                    3700 Trammell Crow Center
                    2001 Ross Avenue
                    Dallas, Texas 75201
                    Facsimile: 214-999-7994

or at such other address as shall be designated by such Person in a written
notice to the other party complying as to delivery with the terms of this
Section.  All such notices, requests, demands and other communications shall,
when mailed or sent, respectively, be effective (i) three (3) days after being
deposited in the mails or (ii) one (1) day after being, deposited with the
express overnight courier service or sent by electronic facsimile transmission,
respectively, addressed as aforesaid.

11.04. Certain Terms. As used herein, the neuter gender shall also be deemed to
denote both the masculine and feminine genders. Unless the context otherwise
requires, the words "hereof", "herein", "hereto" and "hereunder", and words of
similar import, when used in this Agreement shall refer to this Agreement as a
whole and not to any particular term or provision of this Agreement. Whenever
the context requires, the singular form of any noun, pronoun or verb includes
the comparable plural form thereof, and vice versa.

                                       15
<PAGE>

11.05.  Counterparts.  This Agreement may be executed with counterpart signature
pages or in several counterparts which, when executed and delivered by all
parties hereto, shall be binding on all parties hereto and shall constitute one
Agreement, notwithstanding that all parties have not signed the same signature
page or the same counterpart.

11.06.  GOVERNING LAW. THIS AGREEMENT SHALL BE CONSTRUED AND ENFORCED IN
ACCORDANCE WITH, AND SHALL BE GOVERNED BY, THE LAWS OF THE STATE OF ILLINOIS
APPLICABLE TO CONTRACTS EXECUTED IN AND TO BE FULLY PERFORMED IN SUCH STATE.

11.07.  Captions. The headings in this Agreement are for purposes of reference
only and will not be considered in construing this Agreement.

11.08.  Amendments, Waivers, etc.  This Agreement may be amended only by a
written instrument (which may be executed in any number of counterparts) signed
by AROC and the holders of a majority of the Registrable Securities voting as a
class; provided, however, that no such amendment, without the consent of all
holders of Registrable Securities at the time outstanding, shall amend this
Section 11.08. Subject to Section 11.09, no provision of this Agreement may be
waived except by a written instrument signed by the party hereto sought to be
bound.  No failure or delay by any party hereto in exercising any right or
remedy hereunder or under applicable law will operate as a waiver thereof, and a
waiver of a particular right or remedy on one occasion will not be deemed a
waiver of any other right or remedy, or a waiver on any subsequent occasion.

11.09.  Consents of Holders of Registrable Securities.  Any consent of the
holders of Registrable Securities pursuant to this Agreement, and any waiver by
such holders of any provision of this Agreement, shall be in writing (which may
be executed in any number of counterparts) and may be given or taken by the
holders of a majority of the Registrable Securities voting as a class; provided,
however, that no such consent or waiver, without the consent of all holders of
Registrable Securities at the time outstanding, shall amend this Section 11.09;
and any such consent or waiver so given or taken will be binding on all the
holders of Registrable Securities.

11.10.  Recapitalization, Exchanges, etc., Affecting AROC's Capital Stock. The
provisions of this Agreement shall apply, to the full extent set forth herein
with respect to any and all shares of capital stock of AROC or any successor or
assign of AROC (whether by merger, consolidation, sale of assets or otherwise)
which may be issued in respect of, in exchange for or in substitution of, the
Registrable Securities and shall be appropriately adjusted for any stock
dividends, splits, reverse splits, combinations, recapitalization and the like
occurring after the date hereof.

11.11.  Delay of Registration.  No holder of Registrable Securities shall have
any right to obtain or seek an injunction restraining or otherwise delaying any
such registration as the result of any controversy that might arise with respect
to the interpretation or implementation of this Agreement.

11.12.  Prior Agreements.  This Agreement supersedes the Registration Rights
Agreement between AROC and LaSalle dated as of October 13, 1999, which shall be
of no further force or effect.

Section 12.  Listing on Securities Exchanges, etc. AROC shall, promptly after
the registration and sale thereof, use its best efforts to cause any Registrable
Securities (a) to be listed on a national securities exchange and on each
additional national securities exchange on which similar securities of AROC are
listed, if the listing is then permitted under the rules of such exchange, or
(b) to be designated as National Association of Securities Dealers Automated
Quotation System ("NASDAQ") "national market system

                                       16
<PAGE>

securities" within the meaning of Rule llAa2-1 under the Exchange Act if similar
securities of AROC are so designated.

Section 13. Limitation on Registration Rights.

     Notwithstanding anything to the contrary contained herein, (a) the rights
of a holder of Registrable Securities under Section 3 hereof shall be terminated
on the tenth anniversary of the date hereof, (b) the rights of a holder of
Registrable Securities under Section 2 hereof shall be terminated on the tenth
anniversary of the date hereof, (c) prior to such time registration rights under
Sections 2 and 3 may be transferred only to transferees that, together with
their respective Affiliates, are Significant Holders (after giving effect to all
such transfers) and (d) no transfer of registration rights under Sections 2 and
3 may be made except in accordance with the terms and conditions set forth
herein, in the Warrants, and in the Warrant Agreements.

In addition, the rights and obligations under this Agreement shall automatically
be transferred to and binding on any transferee or assignee of the Registrable
Securities, provided that, such transferee or assignee:

     (i)   notifies AROC in writing, within a reasonable time after such
transfer, of the name and address of such transferee or assignee and the
Registrable Securities with respect to which such registration rights are being
transferred or assigned;

     (ii)  agrees in writing to be bound by and subject to the terms and
conditions of this Agreement;

     (iii) receives the Registrable Securities in a transaction that is in
compliance with the requirements for an exemption from the registration
requirements of the Securities Act and applicable state securities laws;

     (iv)  immediately following such transfer, is subject to restrictions under
the Securities Act on further disposition of such Registrable Securities; and

     (v)   acquires at least 33% of the total of the Registrable Securities the
Investor is entitled to acquire under the Warrant Agreements and the Registrable
Securities the Investor currently holds.

                                       17
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have duly executed this Amended and
Restated Registration Rights Agreement as of the date first written above.

                                    AROC INC.

                                    By:_________________________________________
                                    Name:_______________________________________
                                    Title:______________________________________


                                    BANK OF AMERICA, N.A.


                                    By:_________________________________________
                                    Name:_______________________________________
                                    Title:______________________________________


                                    LASALLE STREET NATURAL RESOURCES CORPORATION


                                    By:_________________________________________
                                    Name:_______________________________________
                                    Title:______________________________________

                                       18
<PAGE>

                                   EXHIBIT A
                                      to
                         Registration Rights Agreement

1.  Registration Rights Agreement by and among American Rivers Oil Company, a
Delaware corporation, and F. Fox Benton, Jr., Lizinka M. Benton, F. Fox Benton
III, Lizinka C. Benton and Lucia T. Benton, dated as of October 13, 1999.

2.  Amended and Restated Registration Rights Agreement by and among AROC Inc.,
EnCap Equity 1996 Limited Partnership, EnCap Equity 1994 Limited Partnership,
Energy Capital Investment Company Plc, Shahara Oil, L.L.C., Picosa Creek Limited
Partnership, EF-II Holdings, LLC and El Paso Capital Investments, L.L.C., dated
as of April 30, 2000.

                                       19