Exhibit 10.2

REGISTRATION RIGHTS AGREEMENT

by and between

RIO VISTA ENERGY PARTNERS L.P.

and

TCW ENERGY X BLOCKER (RIO VISTA), L.L.C.

 

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REGISTRATION RIGHTS AGREEMENT

THIS REGISTRATION RIGHTS AGREEMENT (this “Agreement”) is made and entered into
as of May 27, 2009, by and between RIO VISTA ENERGY PARTNERS L.P., a Delaware
limited partnership (the “Company”), and TCW ENERGY X BLOCKER (RIO VISTA),
L.L.C., a Delaware limited liability company (“TCW”).

RECITALS:

A. The Company, TCW, Rio Vista Energy ECO LLC, and TCW Asset Management Company
have entered into a Settlement Agreement dated as of May 27, 2009 (the
“Settlement Agreement”).

B. Pursuant to the Settlement Agreement, the Company has agreed to provide the
registration and other rights set forth in this Agreement for the benefit of
TCW.

AGREEMENT:

NOW THEREFORE, in consideration of the mutual covenants and agreements set forth
herein and for good and valuable consideration, the receipt and sufficiency of
which is hereby acknowledged by each party hereto, the parties hereby agree as
follows:

ARTICLE I
DEFINITIONS

Section 1.1. Definitions. The terms set forth below are used herein as so
defined:

"Affiliate” means, with respect to a specified Person, any other Person,
directly or indirectly controlling, controlled by or under direct or indirect
common control with such specified Person. For purposes of this definition,
“control” (including, with correlative meanings, “controlling,” “controlled by”
and “under common control with”) means the power to direct or cause the
direction of the management and policies of such Person, directly or indirectly,
whether through the ownership of voting securities, by contract or otherwise.

"Affiliate Transfer” means any transfer of Registrable Securities (or the rights
granted to TCW by the Company under this Agreement) from TCW to an Affiliate of
TCW and any successive Affiliate Transfers.

"Business Day” means any day other than a Saturday, Sunday, or a legal holiday
for commercial banks in Houston, Texas.

"Commission” means the United States Securities and Exchange Commission.

"Common Units” means the common units of the Company.

"Exchange Act” means the Securities Exchange Act of 1934, as amended, and the
rules and regulations of the Commission promulgated thereunder.

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"Indemnified Persons” has the meaning specified in Section 2.6(a).

"Losses” has the meaning specified in Section 2.6(a).

"Person” means any individual, corporation, company, voluntary association,
partnership, joint venture, trust, limited liability company, unincorporated
organization, government or any agency, instrumentality or political subdivision
thereof, or any other form of entity.

"Piggyback Registration” has the meaning specified in Section 2.1(a).

"Registrable Securities” means the Common Units, or such other equity securities
issued in exchange therefor in connection with any merger, consolidation or
other business combination involving the Company until such time as such
securities cease to be Registrable Securities pursuant to Section 1.2.

"Registration Expenses” has the meaning specified in Section 2.5(a).

"Rule 144” means Rule 144 as promulgated under the Securities Act.

"Securities Act” means the Securities Act of 1933, as amended, and the rules and
regulations of the Commission promulgated thereunder.

"Selling Expenses” has the meaning specified in Section 2.5(a).

"Settlement Agreement” has the meaning specified in the recitals to this
Agreement.

"Underwritten Offering” means an offering in which Common Units are sold to an
underwriter on a firm commitment basis for reoffering to the public or an
offering that is a “bought deal” with one or more investment banks.

Section 1.2. Registrable Securities. Any Registrable Security will cease to be a
Registrable Security when (a) a registration statement covering such Registrable
Security has been declared effective by the Commission and such Registrable
Security has been sold or disposed of pursuant to such effective registration
statement; (b) such Registrable Security has been disposed of pursuant to any
section of Rule 144 (or any similar provision then in force under the Securities
Act); (c) such Registrable Security is held by the Company or one of its
subsidiaries or (d) such Registrable Security has been sold in a private
transaction in which the transferor’s rights under this Agreement are not
assigned to the transferee of such securities.

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ARTICLE II
REGISTRATION RIGHTS

Section 2.1. Piggyback Registration.

(a) Right to Piggyback. If, at any time after the date of the Settlement
Agreement, the Company proposes to register any of its securities under the
Securities Act in connection with a public offering of such securities (other
than a registration relating solely to the sale of securities to participants in
a common unit incentive plan of the Company, in their capacity as such) and the
registration form to be used may be used for the registration of Registrable
Securities (a “Piggyback Registration”), the Company will give prompt written
notice (and in any event within five Business Days after its receipt of notice
of any exercise of demand registration rights) to TCW, which notice shall
describe the offering contemplated thereby, of its intention to effect such a
registration, and will include in such registration all Registrable Securities
held by TCW (in accordance with the priorities set forth in Section 2.1(b)
below) with respect to which the Company has received written requests for
inclusion within 20 days after the delivery of the Company’s notice.

(b) Allocation and Priority of Registrable Securities in a Piggyback
Registration.

(i) Priority on Primary Registrations. If a Piggyback Registration is an
underwritten primary registration on behalf of the Company and the managing
underwriters advise the Company in writing that in their opinion the number of
securities requested to be included in the registration creates a substantial
risk that the price per unit of Common Units in the offering will be reduced,
the Company will include in such registration first, the securities that the
Company proposes to sell, second, the Registrable Securities requested to be
included in such registration by TCW, and third, pro rata among any other
securities requested to be included in such registration.

(ii) Priority on Secondary Registrations. If a Piggyback Registration is an
underwritten secondary registration on behalf of holders of the Company’s
securities and the managing underwriters advise the Company in writing that in
their opinion the number of securities requested to be included in the
registration creates a substantial risk that the price per share of Common Units
in the offering will be reduced, the Company will include in such registration
first, the Registrable Securities requested to be included therein by TCW,
second, pro rata among the holders of the Company’s securities on the basis of
the number of units of Common Units or Registrable Securities owned by such
holders, with further successive pro rata allocations among such holders if any
such holder has requested the registration of less than all of the Registrable
Securities such holder is entitled to register, and third, other securities
requested to be included in such registration.

Section 2.2. Underwritten Offering.

(a) Underwritten Offering. If, and to the extent that, TCW is unable to
participate in a Piggyback Registration, and TCW elects to otherwise dispose of
its Registrable Securities pursuant to an Underwritten Offering, then the
Company shall take all such other reasonable actions as are requested by the
managing underwriter in order to expedite or facilitate the registration and
disposition of such Registered Securities in an Underwritten Offering, provided,
that the managing underwriter reasonably anticipates gross proceeds from such
Underwritten Offering of at least $10 million, and provided further, that the
Company shall not be required to cause officers of the Company or its Affiliates
to participate in a “road show” or similar marketing effort being conducted by
such managing underwriter with respect to such Underwritten Offering.

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(b) General Procedures. In connection with an Underwritten Offering, TCW and the
Company shall be obligated to enter into an underwriting agreement which
contains such representations, covenants, indemnities and other rights and
obligations as are customary in underwriting agreements for firm commitment
offerings of securities. TCW may not participate in such Underwritten Offering
unless it agrees to sell its Registrable Securities on the basis provided in
such underwriting agreement and completes and executes all questionnaires,
powers of attorney, indemnities and other documents reasonably required under
the terms of such underwriting agreement. TCW may, at its option, require that
any or all of the representations and warranties by, and the other agreements on
the part of, the Company to and for the benefit of such underwriters also be
made to and for TCW’s benefit and that any or all of the conditions precedent to
the obligations of such underwriters under such underwriting agreement also be
conditions precedent to its obligations. TCW 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 TCW
and its ownership of the securities being registered on its behalf and its
intended method of distribution and any other representation required by law. If
TCW disapproves of the terms of an underwriting, it may elect to withdraw
therefrom by notice to the Company and the managing underwriter; provided,
however, that such withdrawal may be made up to and including the time of
pricing of the Underwritten Offering. No such withdrawal or abandonment shall
affect the Company’s obligation to pay Registration Expenses.

(c) Appointment of Underwriters. In connection with an Underwritten Offering,
TCW shall have the sole right to appoint the managing underwriters.

Section 2.3. Registration Procedures. In connection with its obligations
contained in Sections 2.1 and 2.2 hereof, the Company will, as expeditiously as
possible:

(a) furnish to TCW (i) as far in advance as reasonably practicable before filing
any registration statement contemplated by this Agreement or any supplement or
amendment thereto (excluding documents filed pursuant to the Exchange Act that
are incorporated by reference into any registration statement contemplated by
this Agreement or any supplement or amendment thereto), upon request, copies of
reasonably complete drafts of all such documents proposed to be filed, and
provide TCW the opportunity to object to any information pertaining to TCW and
its plan of distribution that is contained therein and make the corrections
reasonably requested by TCW with respect to such information prior to filing
such registration statement and the prospectus included therein or any
supplement or amendment thereto, and (ii) such number of copies of such
registration statement and the prospectus included therein and any supplements
and amendments thereto as TCW may reasonably request in order to facilitate the
public sale or other disposition of the Registrable Securities covered by such
registration statement;

(b) if applicable, use its commercially reasonable efforts to register or
qualify the Registrable Securities covered by any registration statement
contemplated by this Agreement under the securities or blue sky laws of such
jurisdictions as TCW or, in the case of an Underwritten Offering, the managing
underwriter, shall reasonably request, provided that the Company will not be
required to qualify generally to transact business in any jurisdiction where it
is not then required to so qualify or to take any action which would subject it
to general service of process in any such jurisdiction where it is not then so
subject;

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(c) promptly notify TCW and each underwriter of (i) the filing of any
registration statement contemplated by this Agreement or any prospectus or
prospectus supplement to be used in connection therewith, or any amendment or
supplement thereto, and, with respect to such registration statement or any
post-effective amendment thereto, when the same has become effective; and
(ii) any written comments from the Commission with respect to any filing
referred to in clause (i) and any written request by the Commission for
amendments or supplements to the registration statement or any prospectus or
prospectus supplement thereto;

(d) immediately notify TCW and each underwriter, at any time when a prospectus
relating thereto is required to be delivered under the Securities Act, of
(i) the happening of any event as a result of which the prospectus or prospectus
supplement contained in any registration statement contemplated by this
Agreement, as then in effect, 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 in the light of the circumstances
then existing, provided, however, that the Company shall not be required to
specify in the written notice to TCW the nature of such event; (ii) the issuance
or threat of issuance by the Commission of any stop order suspending the
effectiveness of any registration statement contemplated by this Agreement, or
the initiation of any proceedings for that purpose; or (iii) the receipt by the
Company 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; following the provision of such notice, the
Company agrees to as promptly as practicable amend or supplement the prospectus
or prospectus supplement or take other appropriate action so that the prospectus
or prospectus supplement does not include an untrue statement of a material fact
or omit to state a material fact required to be stated therein or necessary to
make the statements therein not misleading in the light of the circumstances
then existing and to take such other action as is necessary to remove such stop
order, suspension, threat thereof or proceedings related thereto;

(e) furnish to TCW copies of any and all transmittal letters or other
correspondence with the Commission or any other governmental agency or
self-regulatory body or other body having jurisdiction (including any domestic
or foreign securities exchange) relating to such offering of Registrable
Securities;

(f) in the case of an Underwritten Offering, furnish upon request, (i) an
opinion of counsel for the Company, dated the effective date of the applicable
registration statement or the date of any amendment or supplement thereto, and
an opinion in customary form dated the date of the closing of the Underwritten
Offering, and (ii) a “cold comfort” letter or letters, dated the date of
execution of the underwriting agreement and a letter or letters of like kind
dated the date of the closing of the Underwritten Offering, in each case, signed
by the independent public accountants who have certified the financial
statements included or incorporated by reference into the applicable
registration statement, and each of the opinion and the “cold comfort” letter or
letters shall be in customary form and covering substantially the same matters
with respect to such registration statement (and the prospectus and any
prospectus supplement included therein) and as are customarily covered in
opinions of issuer’s counsel and in accountants’ letters delivered to the
underwriters in Underwritten Offerings of securities, such other matters as such
underwriters may reasonably request;

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(g) otherwise use its commercially reasonable efforts to comply with all
applicable rules and regulations of the Commission, and make generally available
to its security holders (or otherwise provide in accordance with Section 11(a)
of the Securities Act) an earnings statement satisfying the provisions of
Section 11(a) of the Securities Act in accordance with Rule 158 thereunder (or
any similar rule promulgated under the Securities Act) or otherwise;

(h) make available to the appropriate representatives of the managing
underwriter and TCW access to such information and personnel as is reasonable
and customary to enable such parties to establish a due diligence defense under
the Securities Act; provided that the Company need not disclose any information
to any such representative unless and until such representative has entered into
a confidentiality agreement with the Company;

(i) cause all such Registrable Securities registered pursuant to this Agreement
to be listed on each securities exchange or nationally recognized quotation
system on which similar securities issued by the Company are then listed;

(j) use its commercially reasonable efforts to cause the Registrable Securities
to be registered with or approved by such other governmental agencies or
authorities as may be necessary by virtue of the business and operations of the
Company to enable TCW to consummate the disposition of such Registrable
Securities;

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

(l) enter into customary agreements and take such other actions as are
reasonably requested by TCW or the underwriters, if any, in order to expedite or
facilitate the disposition of such Registrable Securities.

TCW, upon receipt of notice from the Company of the happening of any event of
the kind described in Section 2.3(d), shall forthwith discontinue disposition of
the Registrable Securities until TCW’s receipt of the copies of the supplemented
or amended prospectus contemplated by Section 2.3(d) or until it is advised in
writing by the Company that the use of the prospectus may be resumed, and has
received copies of any additional or supplemental filings incorporated by
reference in the prospectus, and, if so directed by the Company, TCW will, or
will request the managing underwriter or underwriters, if any, to deliver to the
Company (at the Company’s expense) all copies in their possession or control,
other than permanent file copies then in TCW’s possession, of the prospectus and
any prospectus supplement covering such Registrable Securities current at the
time of receipt of such notice.

Section 2.4. Cooperation by TCW. The Company shall have no obligation to include
in any Piggyback Registration Registrable Securities held by TCW if TCW has
failed to timely furnish such information which, in the opinion of counsel to
the Company, is reasonably required in order for the registration statement or
prospectus supplement, as applicable, to comply with the Securities Act.

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Section 2.5. Expenses.

(a) Certain Definitions. “Registration Expenses” means all expenses incident to
the Company’s performance under or compliance with this Agreement to effect the
registration of Registrable Securities in a Piggyback Registration pursuant to
Section 2.1 or an Underwritten Offering pursuant to Section 2.2, and the
disposition of such securities, including, without limitation, all registration,
filing, securities exchange listing and quotation system fees, all registration,
filing, qualification and other fees and expenses of complying with securities
or blue sky laws, fees of the National Association of Securities Dealers, Inc.,
transfer taxes and fees of transfer agents and registrars, all word processing,
duplicating and printing expenses, the fees and disbursements of counsel and
independent public accountants for the Company, including the expenses of any
special audits or “cold comfort” letters required by or incident to such
performance and compliance. In addition, “Selling Expenses” means all
underwriting fees, discounts and selling commissions allocable to the sale of
the Registrable Securities.

(b) Expenses. The Company will pay all Registration Expenses in connection with
a Piggyback Registration pursuant to Section 2.1 or an Underwritten Offering
pursuant to Section 2.2, whether or not the applicable registration statement
becomes effective or any sale is made pursuant to a Piggyback Registration or an
Underwritten Offering. TCW shall pay all Selling Expenses in connection with any
sale of its Registrable Securities pursuant to this Agreement.

Section 2.6. Indemnification.

(a) By the Company. In the event of a registration of any Registrable Securities
under the Securities Act pursuant to this Agreement, the Company will indemnify
and hold harmless TCW, its Affiliates and their respective directors and
officers, and each underwriter, pursuant to the applicable underwriting
agreement with such underwriter, of Registrable Securities thereunder and each
Person, if any, who controls TCW or underwriter within the meaning of the
Securities Act and the Exchange Act (collectively, the “Indemnified Persons”),
against any losses, claims, damages, expenses or liabilities (including
reasonable attorneys’ fees and expenses) (collectively, “Losses”), joint or
several, to which such Indemnified Person may become subject under the
Securities Act, the Exchange Act or otherwise, insofar as such Losses (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 contemplated by
this Agreement, any preliminary prospectus or final prospectus contained
therein, or any amendment or supplement thereof, or arise out of or are based
upon the omission or alleged omission to state therein a material fact required
to be stated therein or necessary to make the statements therein (in the case of
a prospectus, in the light of the circumstances under which they were made) not
misleading, and will reimburse each such Indemnified Person for any legal or
other expenses reasonably incurred by them in connection with investigating or
defending any such Loss or actions or proceedings within a reasonable time after
such expenses are incurred and the Indemnified Person notifies the Company of
such expenses; provided, however, that the Company will not be liable in any
such case if and to the extent that any such Loss arises out of or is based upon
an untrue statement or alleged untrue statement or omission or alleged omission
so made in conformity with information furnished by such Indemnified Person in
writing specifically for use in any registration statement or prospectus
supplement, as applicable. Such indemnity shall remain in full force and effect
regardless of any investigation made by or on behalf of such Indemnified Person,
and shall survive the transfer of such securities by TCW.

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(b) By TCW. TCW agrees to indemnify and hold harmless the Company, its
Affiliates and their respective directors and officers, and each Person, if any,
who controls the Company within the meaning of the Securities Act or of the
Exchange Act to the same extent as the foregoing indemnity from the Company to
TCW, but only with respect to information regarding TCW furnished in writing by
or on behalf of TCW expressly for inclusion in any registration statement or
prospectus supplement relating to the Registrable Securities, or any amendment
or supplement thereto; provided, however, that the liability of TCW shall not be
greater in amount than the dollar amount of the proceeds (net of any Selling
Expenses) received by TCW from the sale of the Registrable Securities giving
rise to such indemnification.

(c) Notice. Promptly after receipt by an indemnified party hereunder of notice
of the commencement of any action, such indemnified party shall, if a claim in
respect thereof is to be made against the indemnifying party hereunder, notify
the indemnifying party in writing thereof; provided, however, that the failure
to notify the indemnifying party shall not relieve it from any liability that it
may have under this Section 2.6 except to the extent that it has been materially
prejudiced by such failure and, provided, further, that the failure to notify
the indemnifying party shall not relieve it from any liability which it may have
to any indemnified party other than under this Section 2.6. The indemnifying
party shall be entitled to participate in and, to the extent it shall wish, to
assume and undertake the defense thereof 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 and undertake the defense
thereof, the indemnifying party shall not be liable to such indemnified party
under this Section 2.6 for any legal expenses subsequently incurred by such
indemnified party in connection with the defense thereof other than reasonable
costs of investigation and of liaison with counsel so selected; provided,
however, that, (i) if the indemnifying party has failed to assume the defense
and employ counsel or (ii) if the defendants in any such action include both the
indemnified party and the indemnifying party and counsel to the indemnified
party shall have concluded that there may be reasonable defenses available to
the indemnified party that are different from or additional to those available
to the indemnifying party, or if the interests of the indemnified party
reasonably may be deemed to conflict with the interests of the indemnifying
party, then the indemnified party shall have the right to select a separate
counsel and to assume such legal defense and otherwise to participate in the
defense of such action, with the reasonable expenses and fees of such separate
counsel and other reasonable expenses related to such participation to be
reimbursed by the indemnifying party as incurred. Notwithstanding any other
provision of this Agreement, no indemnified party shall settle any action
brought against it with respect to which it is entitled to indemnification
hereunder without the consent of the indemnifying party, unless the settlement
thereof imposes no liability or obligation on, and includes a complete and
unconditional release from all liability of, the indemnifying party and does not
contain any admission of wrongdoing or illegal activity by the indemnified
party.

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(d) Contribution. If the indemnification provided for in this Section 2.6 is
held by a court or government agency of competent jurisdiction to be unavailable
to the Company or TCW or is insufficient to hold them harmless in respect of any
Losses, then each such indemnifying party, in lieu of indemnifying such
indemnified party, shall contribute to the amount paid or payable by such
indemnified party as a result of such Losses, in such proportion as is
appropriate to reflect the relative fault of the Company on the one hand and of
TCW on the other in connection with the statements or omissions which resulted
in such Losses, as well as any other relevant equitable considerations;
provided, however, that in no event shall TCW be required to contribute an
aggregate amount in excess of the dollar amount of proceeds (net of Selling
Expenses) received by TCW from the sale of Registrable Securities giving rise to
such indemnification. The relative fault of the Company on the one hand and TCW
on the other 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 has been made by, or relates to,
information supplied by such party, and the parties’ relative intent, knowledge,
access to information and opportunity to correct or prevent such statement or
omission. The parties hereto agree that it would not be just and equitable if
contributions pursuant to this paragraph 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 above. The amount paid by an
indemnified party as a result of the Losses referred to in the first sentence of
this paragraph shall be deemed to include any legal and other expenses
reasonably incurred by such indemnified party in connection with investigating
or defending any Loss which is the subject of this paragraph. No Person guilty
of fraudulent misrepresentation (within the meaning of Section 11(f) of the
Securities Act) shall be entitled to contribution from any Person who is not
guilty of such fraudulent misrepresentation.

(e) Other Indemnification. The provisions of this Section 2.6 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.

Section 2.7. Rule 144 Reporting. With a view to making available the benefits of
certain rules and regulations of the Commission that may permit the sale of the
Registrable Securities to the public without registration, the Company agrees to
use its commercially reasonable efforts to:

(a) Make and keep public information regarding the Company available, as those
terms are understood and defined in Rule 144 of the Securities Act;

(b) File with the Commission in a timely manner all reports and other documents
required of the Company under the Securities Act and the Exchange Act; and

(c) So long as TCW owns any Registrable Securities, furnish to TCW forthwith
upon request a copy of the most recent annual or quarterly report of the
Company, and such other reports and documents so filed as TCW may reasonably
request in availing itself of any rule or regulation of the Commission allowing
TCW to sell any such securities without registration.

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ARTICLE III
MISCELLANEOUS

Section 3.1. Communications. All notices and other communications provided for
or permitted hereunder shall be made in writing by facsimile, courier service or
personal delivery:

if to TCW, at the most current address given by TCW to the Company in accordance
with the provisions of this Section 3.1, which address initially is c/o TCW
Asset Management Company, 865 South Figueroa Street, Suite 1800, Los Angeles,
California 90017, Attention: R. Blair Thomas, Facsimile: (213) 244-0604, with a
copy to TCW Asset Management Company, 333 Clay Street, Suite 4150, Houston,
Texas 77002, Attention: Patrick Hickey, Facsimile: (713) 615-7460.

if to a permitted transferee of TCW, to such permitted transferee at the address
furnished by such permitted transferee, and

if to the Company, at 1313 E. Alton Gloor Blvd., Suite J, Brownsville, Texas
78526.

All such notices and communications shall be deemed to have been received at the
time delivered by hand, if personally delivered; when receipt acknowledged, if
sent via facsimile; and when actually received, if sent by any other means.

Section 3.2. Successor and Assigns. This Agreement shall inure to the benefit of
and be binding upon the successors and assigns of each of the parties, including
subsequent holders of Registrable Securities to the extent permitted herein.

Section 3.3. Transfer or Assignment of Registration Rights. The rights granted
to TCW by the Company under this Agreement may be transferred or assigned by TCW
to one or more transferee(s) or assignee(s) of such Registrable Securities,
provided that (x) the Company is given written notice prior to any said transfer
or assignment, stating the name and address of each such transferee and
identifying the securities with respect to which such registration rights are
being transferred or assigned, and (y) each such transferee assumes in writing
responsibility for its portion of the obligations of TCW under this Agreement;
and provided further, that the requirements in this Section 3.3 shall not apply
to an Affiliate Transfer.

Section 3.4. Recapitalization, Exchanges, etc. Affecting the Common Units. The
provisions of this Agreement shall apply to the full extent set forth herein
with respect to any and all Common Units or other partnership interests of the
Company or any successor or assign of the Company (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, including any
common units or other equity securities that may be issued in exchange for
Registrable Securities in connection with any merger, consolidation or other
business combination involving the Company, and shall be appropriately adjusted
for combinations, recapitalizations and the like occurring after the date of
this Agreement. The Company shall not merge, consolidate or combine with any
other Person unless the agreement providing for such merger, consolidation or
combination expressly provides for the continuation of the registration rights
specified in this Agreement with respect to the Common Units or other equity
securities issued pursuant to such merger, consolidation or combination.

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Section 3.5. Specific Performance. Damages in the event of breach of this
Agreement by a party hereto may be difficult, if not impossible, to ascertain,
and it is therefore agreed that each such Person, in addition to and without
limiting any other remedy or right it may have, will have the right to an
injunction or other equitable relief, including specific performance, in any
court of competent jurisdiction, enjoining any such breach, and enforcing
specifically the terms and provisions hereof, and each of the parties hereto
hereby waives any and all defenses it may have on the ground of lack of
jurisdiction or competence of the court to grant such an injunction or other
equitable relief. The existence of this right will not preclude any such Person
from pursuing any other rights and remedies at law or in equity which such
Person may have.

Section 3.6. Counterparts. This Agreement may be executed in any number of
counterparts and by different parties hereto in separate counterparts, each of
which counterparts, when so executed and delivered, shall be deemed to be an
original and all of which counterparts, taken together, shall constitute but one
and the same Agreement.

Section 3.7. Headings. The headings in this Agreement are for convenience of
reference only and shall not limit or otherwise affect the meaning hereof.

Section 3.8. Governing Law. The laws of the State of New York shall govern this
Agreement without regard to principles of conflict of laws.

Section 3.9. Severability of Provisions. Any provision of this Agreement which
is prohibited or unenforceable in any jurisdiction shall, as to such
jurisdiction, be ineffective to the extent of such prohibition or
unenforceability without invalidating the remaining provisions hereof or
affecting or impairing the validity or enforceability of such provision in any
other jurisdiction.

Section 3.10. Entire Agreement. This Agreement is intended by the parties as a
final expression of their agreement and intended to be a complete and exclusive
statement of the agreement and understanding of the parties hereto in respect of
the subject matter contained herein. There are no restrictions, promises,
warranties or undertakings, other than those set forth or referred to herein
with respect to the rights granted by the Company set forth herein. This
Agreement supersedes all prior agreements and understandings between the parties
with respect to such subject matter.

Section 3.11. Amendment. This Agreement may be amended only by means of a
written amendment signed by the Company and TCW.

Section 3.12. No Presumption. In the event any claim is made by a party relating
to any conflict, omission, or ambiguity in this Agreement, no presumption or
burden of proof or persuasion shall be implied by virtue of the fact that this
Agreement was prepared by or at the request of a particular party or its
counsel.

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IN WITNESS WHEREOF, the parties have executed this Agreement as of the date
first written above.

RIO VISTA ENERGY PARTNERS L.P.

By: Rio Vista GP LLC, its sole general partner

By:
                                                                                        
Name: Ian Bothwell
Title: Manager and Acting CEO

TCW ENERGY X BLOCKER (RIO VISTA), L.L.C.

By: TCW Asset Management Company, as Manager

By:
                                                                                        
Name: Curt S. Taylor
Title: Senior Vice President

By:
                                                                                        
Name: Patrick H. Hickey
Title: Senior Vice President

SIGNATURE PAGE—REGISTRATION RIGHTS AGREEMENT

 

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