COSTILLA ENERGY INC
S-1, 1996-07-26
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<PAGE>
     AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON JULY 26, 1996
 
                                                   REGISTRATION NO. 333-
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
 
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                           --------------------------
 
                                    FORM S-1
 
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933
                            ------------------------
 
                             COSTILLA ENERGY, INC.
             (Exact name of Registrant as specified in its charter)
 
<TABLE>
<S>                              <C>                             <C>
            DELAWARE                           1311                     75-2658940
 (State or other jurisdiction of   (Primary Standard Industrial      (I.R.S. Employer
 incorporation or organization)    Classification Code Number)     Identification No.)
</TABLE>
 
                           --------------------------
 
                         400 WEST ILLINOIS, SUITE 1000
                              MIDLAND, TEXAS 79701
                                 (915) 683-3092
              (Address, including zip code, and telephone number,
       including area code, of Registrant's principal executive offices)
 
                          MICHAEL J. GRELLA, PRESIDENT
                             COSTILLA ENERGY, INC.
                         400 WEST ILLINOIS, SUITE 1000
                              MIDLAND, TEXAS 79701
                                 (915) 683-3092
           (Name, address, including zip code, and telephone number,
                   including area code, of agent for service)
                           --------------------------
 
                                   COPIES TO:
 
<TABLE>
<S>                                                 <C>
               Richard T. McMillan                                   R. Joel Swanson
         Cotton, Bledsoe, Tighe & Dawson,                         Baker & Botts, L.L.P.
            a Professional Corporation                                910 Louisiana
                500 West Illinois                                  Houston, Texas 77002
                    Suite 300
               Midland, Texas 79701
</TABLE>
 
                           --------------------------
 
    APPROXIMATE  DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC: As soon as
practicable after this Registration Statement becomes effective.
 
    If any of the securities being registered on this Form are to be offered  on
a  delayed or continuous basis pursuant to  Rule 415 under the Securities Act of
1933, check the following box: / /
 
    If this Form  is filed  to register  additional securities  for an  offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and  list  the  Securities  Act registration  statement  number  of  the earlier
effective registration statement for the same offering. / /
 
    If this Form  is a post-effective  amendment filed pursuant  to Rule  462(c)
under  the Securities Act, check  the following box and  list the Securities Act
registration statement number  of the earlier  effective registration  statement
for the same offering. / /
 
    If  delivery of the Prospectus is expected  to be made pursuant to Rule 434,
please check the following box. / /
 
                        CALCULATION OF REGISTRATION FEE
 
<TABLE>
<CAPTION>
                                                    PROPOSED OFFERING    PROPOSED MAXIMUM
    TITLE OF EACH CLASS OF         AMOUNT TO BE      PRICE PER SHARE    AGGREGATE OFFERING      AMOUNT OF
 SECURITIES TO BE REGISTERED      REGISTERED (1)           (2)              PRICE (2)        REGISTRATION FEE
<S>                             <C>                 <C>                 <C>                 <C>
Common Stock, $0.10 par value       4,600,000             $16.00           $73,600,000           $25,379
</TABLE>
 
(1) Includes  an  aggregate  of  600,000  shares  subject  to  an  Underwriters'
    over-allotment option.
 
(2) Estimated solely for the purpose of calculating the registration fee.
                           --------------------------
 
    THE  REGISTRANT HEREBY  AMENDS THIS REGISTRATION  STATEMENT ON  SUCH DATE OR
DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL
FILE A  FURTHER  AMENDMENT  WHICH SPECIFICALLY  STATES  THAT  THIS  REGISTRATION
STATEMENT  SHALL THEREAFTER BECOME EFFECTIVE IN  ACCORDANCE WITH SECTION 8(A) OF
THE SECURITIES ACT  OF 1933  OR UNTIL  THE REGISTRATION  STATEMENT SHALL  BECOME
EFFECTIVE  ON SUCH DATE AS THE COMMISSION, ACTING PURSUANT TO SAID SECTION 8(A),
MAY DETERMINE.
 
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
<PAGE>
                             CROSS REFERENCE SHEET
                  (PURSUANT TO ITEM 501(B) OF REGULATION S-K)
 
<TABLE>
<CAPTION>
                    ITEM NUMBER AND HEADING                                 LOCATION OR CAPTION IN PROSPECTUS
- ----------------------------------------------------------------  -----------------------------------------------------
<C>        <S>                                                    <C>
       1.  Forepart of the Registration Statement and Outside
            Front Cover of Prospectus...........................  Outside Front Cover Page
       2.  Inside Front and Outside Back Cover Pages of
            Prospectus..........................................  Inside Front and Outside Back Cover Pages
       3.  Summary Information, Risk Factors and Ratio of
            Earnings to Fixed Charges...........................  Prospectus Summary; Risk Factors; The Company; Pro
                                                                   Forma Condensed Financial Statements; Selected
                                                                   Financial Information
       4.  Use of Proceeds......................................  Prospectus Summary; Use of Proceeds
       5.  Determination of Offering Price......................  Outside Front Cover Page; Underwriting
       6.  Dilution.............................................  Risk Factors; Dilution
       7.  Selling Security Holders.............................  *
       8.  Plan of Distribution.................................  Outside Front Cover Page; Underwriting
       9.  Description of Securities to Be Registered...........  Outside Front Cover Page; Prospectus Summary;
                                                                   Description of Capital Stock
      10.  Interests of Named Experts and Counsel...............  *
      11.  Information with Respect to the Registrant...........  Prospectus Summary; Risk Factors; The Company;
                                                                   Dividend Policy; Capitalization; Pro Forma Condensed
                                                                   Financial Statements; Selected Financial
                                                                   Information; Management's Discussion and Analysis of
                                                                   Financial Condition and Results of Operations;
                                                                   Business and Properties; Management; Certain
                                                                   Transactions; Security Ownership of Certain
                                                                   Beneficial Owners and Management; Executive
                                                                   Compensation and Other Information; Description of
                                                                   Certain Indebtedness; Description of Capital Stock;
                                                                   Consolidated Financial Statements
      12.  Disclosure of Commission Position on Indemnification
            for Securities Act Liabilities......................  *
</TABLE>
 
- ------------------------
* Omitted because item is not applicable.
<PAGE>
INFORMATION   CONTAINED  HEREIN  IS  SUBJECT   TO  COMPLETION  OR  AMENDMENT.  A
REGISTRATION STATEMENT  RELATING TO  THESE SECURITIES  HAS BEEN  FILED WITH  THE
SECURITIES  AND EXCHANGE  COMMISSION. THESE SECURITIES  MAY NOT BE  SOLD NOR ANY
OFFERS TO BUY BE ACCEPTED PRIOR  TO THE TIME THE REGISTRATION STATEMENT  BECOMES
EFFECTIVE.  THIS  PROSPECTUS  SHALL  NOT  CONSTITUTE AN  OFFER  TO  SELL  OR THE
SOLICITATION OF ANY OFFER TO BUY NOR SHALL THERE BE ANY SALE OF THESE SECURITIES
IN ANY STATE IN WHICH SUCH OFFER,  SOLICITATION OR SALE WOULD BE UNLAWFUL  PRIOR
TO REGISTRATION OR QUALIFICATION UNDER THE SECURITIES LAWS OF ANY SUCH STATE.
<PAGE>
                  SUBJECT TO COMPLETION - DATED JULY 26, 1996
 
PROSPECTUS
- --------------------------------------------------------------------------------
 
                                4,000,000 Shares
 
                             COSTILLA ENERGY, INC.
 
                                  Common Stock
- -------------------------------------------------------------------------
 
All  of the shares  of the Common  Stock, $0.10 par  value (the "Common Stock"),
offered hereby (the "Common Stock Offering") are being sold by Costilla  Energy,
Inc., a Delaware corporation ("Costilla" or the "Company").
 
Concurrently   with  the  Common   Stock  Offering,  the   Company  is  offering
$100,000,000 of     % Senior Subordinated Notes due 2006 (the "Notes") for  sale
to  the  public  (the  "Notes  Offering," and  together  with  the  Common Stock
Offering, the  "Offerings") pursuant  to an  underwritten public  offering.  The
Notes  Offering  and  the Common  Stock  Offering  are each  conditioned  on the
consummation of the other.
 
Prior to this Common  Stock Offering, there  has been no  public market for  the
Common Stock of the Company. It is currently anticipated that the initial public
offering  price will be between $14.00  and $16.00 per share. See "Underwriting"
for a discussion  of the  factors to be  considered in  determining the  initial
public  offering price. The Company will apply for inclusion of the Common Stock
on The  Nasdaq Stock  Market's National  Market (the  "Nasdaq National  Market")
under the trading symbol "COSE."
 
SEE "RISK FACTORS" ON PAGES 9 TO 13 FOR A DISCUSSION OF CERTAIN MATERIAL FACTORS
THAT  SHOULD BE CONSIDERED IN CONNECTION WITH  AN INVESTMENT IN THE COMMON STOCK
OFFERED HEREBY.
- --------------------------------------------------------------------------------
 
THESE SECURITIES HAVE NOT BEEN APPROVED  OR DISAPPROVED BY THE SECURITIES  AND
  EXCHANGE  COMMISSION  OR  ANY  STATE  SECURITIES  COMMISSION  NOR  HAS THE
    SECURITIES AND EXCHANGE COMMISSION OR ANY STATE SECURITIES  COMMISSION
      PASSED  UPON  THE  ACCURACY  OR ADEQUACY  OF  THIS  PROSPECTUS. ANY
       REPRESENTATION  TO   THE   CONTRARY   IS   A   CRIMINAL   OFFENSE.
 
<TABLE>
<CAPTION>
                                                                  Underwriting
                                                   Price to       Discounts and     Proceeds to
                                                    Public       Commissions (1)    Company (2)
<S>                                             <C>              <C>              <C>
Per Share.....................................         $                $                $
Total (3).....................................         $                $                $
</TABLE>
 
(1) The Company has agreed to indemnify the several Underwriters against certain
    liabilities,  including liabilities  under the  Securities Act  of 1933. See
    "Underwriting."
 
(2) Before deducting expenses payable by the Company estimated to be $      .
 
(3) The Company  has granted  the several Underwriters  a 30-day  over-allotment
    option  to purchase up to  600,000 additional shares of  Common Stock on the
    same terms and conditions as set forth above. If all such additional  shares
    are  purchased  by  the Underwriters,  the  total  Price to  Public  will be
    $      , the total Underwriting Discounts and Commissions will be $      and
    the total Proceeds to Company will be $      . See "Underwriting."
- --------------------------------------------------------------------------------
 
The shares of Common  Stock are offered by  the several Underwriters subject  to
delivery by the Company and acceptance by the Underwriters, to prior sale and to
withdrawal,  cancellation or modification of  the offer without notice. Delivery
of the  shares to  the Underwriters  is expected  to be  made at  the office  of
Prudential  Securities Incorporated, One New York  Plaza, New York, New York, on
or about             , 1996.
 
PRUDENTIAL SECURITIES INCORPORATED  RAUSCHER PIERCE REFSNES, INC.
 
August   , 1996
<PAGE>
                             COSTILLA ENERGY, INC.
                                GEOGRAPHIC FOCUS
 
         [GRAPHIC MATERIAL, AND DESCRIPTION THEREOF FOR EDGAR, TO COME]
 
                            ------------------------
 
    IN CONNECTION WITH THIS OFFERING, THE UNDERWRITERS MAY OVER-ALLOT OR  EFFECT
TRANSACTIONS WHICH STABILIZE OR MAINTAIN THE MARKET PRICE OF THE COMMON STOCK AT
A  LEVEL  ABOVE THAT  WHICH MIGHT  OTHERWISE  PREVAIL IN  THE OPEN  MARKET. SUCH
STABILIZATION, IF COMMENCED, MAY BE DISCONTINUED AT ANY TIME.
 
                                       2
<PAGE>
                               PROSPECTUS SUMMARY
 
    THE  FOLLOWING  SUMMARY  IS  QUALIFIED  IN  ITS  ENTIRETY  BY  THE  DETAILED
INFORMATION, FINANCIAL STATEMENTS  AND OTHER  DATA APPEARING  ELSEWHERE IN  THIS
PROSPECTUS. THE PRO FORMA INFORMATION GIVES EFFECT TO THE CONVERSION OF COSTILLA
FROM A LIMITED LIABILITY COMPANY TO A CORPORATION, CERTAIN MATERIAL ACQUISITIONS
AND  THE OFFERINGS AND THE APPLICATION  OF THE ESTIMATED NET PROCEEDS THEREFROM.
SEE "-- SIGNIFICANT  ACQUISITIONS," "THE COMPANY  -- CORPORATE  REORGANIZATION,"
AND  "USE OF PROCEEDS." AS USED HEREIN, REFERENCES TO THE COMPANY OR TO COSTILLA
ARE TO COSTILLA ENERGY, INC.  AND ITS SUBSIDIARIES. UNLESS OTHERWISE  INDICATED,
THE  INFORMATION  IN THIS  PROSPECTUS  ASSUMES THE  UNDERWRITERS' OVER-ALLOTMENT
OPTION WILL NOT BE EXERCISED. CERTAIN OIL AND GAS TERMS USED IN THIS  PROSPECTUS
ARE DEFINED IN THE "GLOSSARY" INCLUDED HEREIN.
 
                                  THE COMPANY
 
    Costilla  is  an  independent  energy company  engaged  in  the exploration,
acquisition and development  of oil  and gas properties.  The Company's  primary
operations  are in  the Permian  Basin, the  Gulf Coast  and the  Rocky Mountain
regions. The  Company's  strategy  focuses  on  increasing  reserves  through  a
targeted  exploration program, the  exploitation of its  existing properties and
selective property acquisitions. In addition,  the Company recently acquired  an
interest  in  a  concession for  the  development  of mineral  interests  in the
Republic of Moldova, in Eastern Europe. The Company also has minor interests  in
the domestic gas gathering and transmission business.
 
    The  Company's  predecessor began  operating in  1988  with the  strategy of
acquiring and exploiting undervalued oil and gas properties, and at December 31,
1992 had net proved reserves  of 4.7 MMBOE. Since  January 1, 1993, the  Company
has  successfully closed seven  transactions for an  aggregate purchase price of
approximately $101  million.  As  of  March 31,  1996,  the  Company  had  total
estimated  net  proved reserves  of 16.5  Mmbbls of  oil and  112.9 Bcf  of gas,
aggregating 35.3  MMBOE, with  a PV-10  Value of  approximately $179.5  million,
assuming the 1996 Acquisition (as defined below) had occurred at March 31, 1996.
The  Company also has  a substantial undeveloped  acreage position consisting of
205,908 gross (141,384 net) acres. The  Company has identified in excess of  200
drilling locations of which 82 are included in its proved reserves.
 
    Costilla   has  in-house  exploration  expertise   which  uses  3-D  seismic
technology as  a  primary  tool  to  identify  drilling  opportunities  and  has
experienced  high rates of  success in each  of its first  two major 3-D seismic
drilling programs. Since 1994, the Company  has drilled 23 wells based on  these
3-D  surveys,  20  of  which  have been  productive.  The  Company  has recently
completed a third  3-D survey  in Pecos County,  Texas and  intends to  commence
drilling  on this acreage in  the second half of  1996. Moreover, the Company is
currently conducting two additional 3-D surveys. The Company currently plans  to
drill 81 wells through 1997 based on its 3-D surveys.
 
    Since   1993,  Costilla  has  generated   significant  growth  in  reserves,
production and EBITDA. The Company increased its estimated proved reserves  from
6.0  MMBOE at December 31, 1993  to 35.3 MMBOE at March  31, 1996 (pro forma for
the 1996 Acquisition), representing a compound annual growth rate of 114%.  This
reserve  growth has been achieved at an average all-in finding cost of $3.49 per
BOE over such period, a level which the Company believes is lower than  industry
averages.  Concurrently, the Company increased  its average net daily production
from 827 BOE for the  year ended December 31, 1993  to 10,703 BOE for the  three
months ended March 31, 1996 (pro forma for the 1996 Acquisition), representing a
compound  annual growth rate of 195%. EBITDA increased at a 240% compound annual
growth rate from $1.8 million for 1993 to $20.8 million for 1995 (pro forma  for
the 1995 Acquisition and the 1996 Acquisition).
 
                                       3
<PAGE>
                               BUSINESS STRATEGY
 
    The  Company's strategy is to increase  its oil and gas reserves, production
and cash flow from operations through  a two-pronged approach which combines  an
active  exploration program using  3-D seismic and  other technological advances
with the acquisition and exploitation of producing properties. The Company seeks
to reduce its operating  and commodity risks by  holding a diverse portfolio  of
properties.  The  Company also  seeks  to manage  the  elements of  its business
strategy through the operation of a  significant portion of its properties,  the
use  of  a disciplined  rate of  return  analysis and  the direct  marketing and
hedging of its oil  and gas production. The  elements of the Company's  strategy
may be further described as follows:
 
    - EXPLORATION   EFFORTS.     The  Company  uses   extensive  geological  and
      geophysical analysis  to carefully  focus its  3-D seismic  surveys.  This
      focus  allows the Company to successfully direct the size and scope of its
      exploration program in order  to improve the  likelihood of success  while
      managing  overall exploration costs. The Company's exploration efforts are
      concentrated currently on  known producing regions.  The Company plans  to
      drill 26 exploratory wells during the remainder of 1996 and 36 exploratory
      wells in 1997. Capital budgeted for exploration activities is $8.4 million
      for the last nine months of 1996 and $10.8 million for 1997.
 
    - EXPLOITATION  ACTIVITIES.    The  Company  is  actively  pursuing numerous
      exploitation opportunities within its existing properties, including areas
      where no proved reserves  are currently assigned. Exploitation  activities
      currently  in  progress  include a  carbon  dioxide  flood, recompletions,
      workovers,  infill  and  horizontal  drilling  and  a  secondary  recovery
      project.  The Company's capital budget for such activities is $8.9 million
      for the last nine months of 1996 and $9.2 million for 1997, which includes
      the drilling of 17 development wells  in 1996 and 13 development wells  in
      1997.
 
    - PROPERTY  ACQUISITIONS.  The Company seeks to acquire producing properties
      where it has identified opportunities to increase production and  reserves
      through  both  exploitation and  exploration  activities. The  Company has
      increased the  value  of its  acquisitions  by aggressively  managing  the
      operations  of existing proved properties  and by successfully identifying
      and developing  previously  unproved  reserves on  acquired  acreage.  The
      Company  seeks to acquire reserves which  will fit its existing portfolio,
      are generally  not being  actively marketed  and where  a negotiated  sale
      would  be the method of  purchase. The Company does  not rely on major oil
      company divestitures or property auctions.
 
    - PROPERTY DIVERSIFICATION.  The  Company holds a portfolio  of oil and  gas
      properties  located in  the Permian  Basin, the  Gulf Coast  and the Rocky
      Mountain regions. The Company believes  that by conducting its  activities
      in  distinct  regions  it is  able  to  reduce commodity  price  and other
      operational risks. The Company's Moldovan interest is an extension of this
      strategy and  can  be  characterized by  low  initial  costs,  significant
      reserve  potential  and the  availability of  technical  data that  may be
      further developed by the Company.
 
    - CONTROL OF  OPERATIONS.   The  Company  prefers  to operate  and  own  the
      majority  working  interest in  its  properties. This  allows  the Company
      greater control over future development, drilling, completing and  lifting
      costs  and  marketing of  production. At  December  31, 1995,  the Company
      operated wells constituting  approximately 65%  of its  total PV-10  Value
      (pro forma for the 1996 Acquisition).
 
                                       4
<PAGE>
                            SIGNIFICANT ACQUISITIONS
 
    1995  ACQUISITION.  In  a $46.6 million acquisition  completed in June 1995,
the Company acquired a group  of oil and gas  properties located in the  Permian
Basin,  Gulf Coast and Rocky  Mountain regions. At the  date of acquisition, the
net proved reserves included 6.9 Mmbbls of oil and 40.0 Bcf of gas,  aggregating
13.6  MMBOE. From  the date  of acquisition  until March  31, 1996,  the Company
produced 1.1  MMBOE from  the acquired  properties  and sold  a portion  of  the
acquired  properties for approximately $3.6 million.  At March 31, 1996, the net
proved reserves  of  the remaining  properties  were 13.4  MMBOE.  The  acquired
properties also included 103,010 gross (93,786 net) undeveloped acres.
 
    1996 ACQUISITION.  In June 1996, the Company acquired a group of oil and gas
properties  located primarily  in the Permian  Basin and Gulf  Coast regions for
approximately $42.5  million.  This  acquisition included  properties  with  net
proved  reserves at March  31, 1996 of  5.0 Mmbbls of  oil and 33.5  Bcf of gas,
aggregating 10.6  MMBOE.  The acquired  properties  also included  42,855  gross
(10,172  net) undeveloped acres and a pipeline located in Pennsylvania which had
an allocated purchase price of $3.5 million.
 
                              DRILLING ACTIVITIES
 
    Exploration efforts  since  January 1,  1996  include the  drilling  of  two
successful  wells located on the Company's Edwards/McElroy Ranch 3-D Prospect in
the Permian Basin.  Production from the  initial well averaged  344 BOE per  day
from  its May 11 completion to June 30, 1996, while the second well is currently
being  completed.  These   successful  wells  confirm   the  Company's   seismic
interpretation  of the  continuation of  a significant  trend. As  a result, the
Company has  identified 75  additional drilling  locations, three  of which  are
included  in the Company's  proved reserves. Through June  30, 1996, the Company
had drilled 11 total wells in the  prospect, 10 of which have been completed  as
producing wells.
 
    The  Company has also  drilled three exploratory  wells in the McGyver-Green
Acres 3-D Prospect since  January 1, 1996,  yielding two successful  completions
and  bringing the  total number  of wells  drilled in  that prospect  to 12. The
average daily  production  from the  11  producing  wells in  this  prospect  is
approximately 83 BOE per well. The Company has identified 41 additional drilling
locations  in the McGyver-Green Acres Prospect, 14  of which are included in the
Company's proved reserves.
 
    The Company has  also drilled and  completed five development  wells in  the
Permian Basin and Gulf Coast regions since the beginning of 1996. Currently, the
Company's  principal exploitation activities  include a carbon  dioxide flood in
the East Goldsmith  Unit, infill  drilling primarily  in the  Permian Basin  and
horizontal drilling in the Susan Peak Field.
 
                                       5
<PAGE>
                           THE COMMON STOCK OFFERING
 
<TABLE>
<S>                                              <C>
Common Stock Offered by the Company............  4,000,000 Shares(1)
 
Common Stock to be Outstanding after the
 Offering......................................  10,000,000 Shares(1)
 
Concurrent Notes Offering......................  Concurrently    with   the   Common   Stock
                                                 Offering,   the    Company   is    offering
                                                 $100,000,000  of      % Senior Subordinated
                                                 Notes due 2006.  See "Notes Offering."  The
                                                 closing  of  the  Notes  Offering  and  the
                                                 Common Stock Offering are each  conditioned
                                                 upon the consummation of the other.
 
Use of Proceeds................................  To  repay  existing  indebtedness,  to  pay
                                                 certain costs incurred  in connection  with
                                                 the   Corporate  Reorganization,   and  for
                                                 general corporate  purposes.  See  "Use  of
                                                 Proceeds."
 
Nasdaq National Market Symbol..................  COSE
</TABLE>
 
- ------------------------
(1) Excludes           shares of  Common Stock  reserved for  issuance under the
    Company's employee  benefit plans.  See  "Executive Compensation  and  Other
    Information."
 
                                       6
<PAGE>
                         SUMMARY FINANCIAL INFORMATION
 
    The  following table  sets forth  certain summary  historical and  pro forma
financial data of the Company. The historical data should be read in conjunction
with the  Consolidated  Financial  Statements and  the  notes  thereto  included
elsewhere in this Prospectus. The Company acquired significant producing oil and
gas   properties  in  certain   of  the  periods   presented  which  affect  the
comparability of the  historical financial  and operating data  for the  periods
presented.  The pro forma information should be read in conjunction with the Pro
Forma Condensed Financial  Statements and  notes thereto  included elsewhere  in
this  Prospectus. Neither the  historical results nor the  pro forma results are
necessarily indicative of the Company's future operations or financial results.
 
<TABLE>
<CAPTION>
                                                                                                   THREE MONTHS ENDED
                                                         YEAR ENDED DECEMBER 31,                        MARCH 31,
                                               --------------------------------------------  -------------------------------
                                                         HISTORICAL              PRO FORMA        HISTORICAL       PRO FORMA
                                               -------------------------------  -----------  --------------------  ---------
                                                 1993       1994       1995       1995(1)      1995       1996      1996(1)
                                               ---------  ---------  ---------  -----------  ---------  ---------  ---------
                                                             (IN THOUSANDS, EXCEPT RATIOS AND PER SHARE DATA)
<S>                                            <C>        <C>        <C>        <C>          <C>        <C>        <C>
STATEMENT OF OPERATIONS DATA:
  Revenues...................................  $   4,397  $   7,836  $  21,816   $  52,637   $   2,180  $   8,951  $  14,038
  Expenses:
    Oil and gas production...................      1,688      2,351     10,355      26,937         896      3,659      6,283
    General and administrative...............        952      1,184      3,571       4,850         459      1,362      1,505
    Exploration and abandonments.............        218        793      1,650       2,761       1,007        228        475
    Depreciation, depletion and
     amortization............................        884      1,847      6,095      14,313         462      1,986      3,166
    Interest.................................        605      1,458      4,454      11,631         407      1,704      2,908
    Other....................................         --         --          2           2          --         --         --
  Net income (loss) before income taxes......         50        203     (4,311)     (7,857)     (1,051)        12       (299)
  Pro forma earnings (loss) per common
   share.....................................         --         --         --       (0.80)         --         --      (0.03)
  Pro forma weighted average common shares
   outstanding...............................         --         --         --       9,861          --         --     10,000
STATEMENT OF CASH FLOWS DATA:
  Net cash provided by (used in):
    Operating activities.....................  $     322  $   1,527  $   6,366          --   $  (1,827) $   2,276         --
    Investing activities.....................     (6,731)   (12,146)   (62,467)         --      (1,389)    (5,132)        --
    Financing activities.....................      6,315     10,618     58,830          --       3,272      3,000         --
OTHER FINANCIAL DATA:
  Capital expenditures.......................  $   6,862  $  11,868  $  62,220          --   $   1,389  $   5,132         --
  EBITDA (2).................................      1,757      4,301      7,888   $  20,848         825      3,930  $   6,250
  EBITDA/Interest expense (3)................        2.9x       2.9x       1.8x        1.8x        2.0x       2.3x       2.1x
  Ratio of earnings to fixed charges (4).....        1.0        1.1         --          --          --        1.0         --
BALANCE SHEET DATA (AS OF PERIOD END):
  Working capital............................  $   1,612  $   1,081  $   2,496          --          --  $   2,104  $  15,955
  Total assets...............................     13,365     24,904     87,367          --          --     91,024    145,117
  Total debt.................................     12,006     23,591     71,494          --          --     74,494    100,000
  Redeemable members' capital................         --         --     11,320          --          --     11,678         --
  Members' capital...........................         51       (747)    (7,189)         --          --     (7,535)        --
  Pro forma stockholders' equity.............         --         --         --          --          --         --     35,843
</TABLE>
 
- ------------------------------
(1)  Assumes that  the 1995  Acquisition, the  1996 Acquisition,  the  Corporate
     Reorganization (as defined in "The Company-- Corporate Reorganization") and
     the  Offerings and the application of proceeds therefrom had taken place on
     March 31, 1996 for purposes  of the Balance Sheet  Data (to the extent  not
     already  reflected) and as of January 1,  1995 for purposes of Statement of
     Operations Data and Other Financial Data.
 
(2)  EBITDA is presented because of its wide acceptance as a financial indicator
     as to a company's ability to service or incur debt. EBITDA (as used herein)
     is calculated by adding interest, income taxes, depreciation, depletion and
     amortization and exploration  and abandonment costs  to net income  (loss).
     EBITDA  should not be considered as an alternative to earnings (loss) as an
     indicator of  the Company's  financial performance  or to  cash flow  as  a
     measure of liquidity.
 
(3)  Calculated  by  dividing  EBITDA by  interest.  Interest  includes interest
     expense accrued and amortization of deferred financing costs.
 
(4)  For purposes  of  calculating  the  ratio of  earnings  to  fixed  charges,
     "earnings" are net income (loss) plus income taxes and fixed charges. Fixed
     charges are comprised of interest on indebtedness, amortization of deferred
     financing costs, and that portion of
 
                                       7
<PAGE>
     operating lease expense which is deemed to be representative of an interest
     factor.  Earnings were insufficient  to cover fixed  charges by $4,314,000,
     and $1,051,000 for the historical periods ended December 31, 1995 and March
     31, 1995,  respectively  and $7,857,000  and  $299,000 for  the  pro  forma
     periods ended December 31, 1995 and March 31, 1996, respectively.
 
                              SUMMARY RESERVE DATA
 
<TABLE>
<CAPTION>
                                                                   AS OF DECEMBER 31,           AS OF MARCH 31, 1996
                                                             -------------------------------  ------------------------
                                                               1993       1994       1995      ACTUAL    PRO FORMA(1)
                                                             ---------  ---------  ---------  ---------  -------------
<S>                                                          <C>        <C>        <C>        <C>        <C>
ESTIMATED PROVED RESERVES (2):
  Oil (MBbls)..............................................      2,365      4,009     10,788     11,479       16,476
  Gas (Mmcf)...............................................     21,619     27,512     78,152     79,420      112,920
  MBOE (6 Mcf/Bbl).........................................      5,968      8,594     23,813     24,716       35,297
  Percent of proved developed reserves.....................       67.0%      62.3%      76.1%      73.9%        78.2%
  Present value of estimated future net cash flow, before
   income taxes, discounted at 10% (in thousands)..........  $  26,377  $  36,779  $ 113,296  $ 129,091    $ 179,527
  Reserve life index (in years) (3)........................       19.7       14.4       13.6         --           --
RESERVE REPLACEMENT DATA:
  Production replacement ratio (4).........................        513%       549%       969%        --           --
  All-in finding costs per BOE (5).........................  $    4.31  $    3.67  $    3.53  $    2.84    $    2.84
</TABLE>
 
- ------------------------------
(1)  Gives effect to  the 1995 Acquisition  and the 1996  Acquisition as if such
    transactions had occurred as of January 1, 1995.
 
(2) Estimates of net proved oil and gas reserves at March 31, 1996 are based  on
    reports  prepared by Williamson  Petroleum Consultants, Inc. ("Williamson"),
    independent petroleum engineers. The 1995 reserve estimates were prepared by
    the Company and such estimates of gross reserves with respect to certain  of
    the  Company's  producing properties  were subject  to  a limited  review by
    Williamson. Prior reserve estimates are based on information compiled by the
    Company. See "Risk Factors  -- Uncertainty of  Estimates of Proved  Reserves
    and  Future  Net  Revenues" and  "Business  and  Properties --  Oil  and Gas
    Reserves."
 
(3) Calculated by dividing year-end proved reserves by annual production for the
    most recent year.
 
(4) Calculated by dividing reserve  additions through acquisitions of  reserves,
    extensions  and discoveries and revisions during  the year by production for
    such year.
 
(5) The average  all-in finding costs  over the period  January 1, 1993  through
    March 31, 1996 (pro forma for the 1996 Acquisition) was $3.49 per BOE.
 
                             SUMMARY OPERATING DATA
 
<TABLE>
<CAPTION>
                                                               YEAR ENDED DECEMBER 31,
                                                    ----------------------------------------------
                                                                                                    THREE MONTHS ENDED MARCH 31,
                                                              HISTORICAL             PRO FORMA(1)               1996
                                                    -------------------------------  -------------  ----------------------------
                                                      1993       1994       1995         1995         ACTUAL      PRO FORMA(1)
                                                    ---------  ---------  ---------  -------------  -----------  ---------------
<S>                                                 <C>        <C>        <C>        <C>            <C>          <C>
PRODUCTION DATA:
  Oil (MBbls).....................................        158        330        950        2,085           338            502
  Gas (Mmcf)......................................        865      1,600      4,806       11,985         1,643          2,832
  MBOE............................................        302        597      1,751        4,083           612            974
AVERAGE SALES PRICE PER UNIT:
  Oil (per Bbl)...................................  $   16.93  $   15.25  $   15.53    $   15.75     $   17.32      $   17.37
  Gas (per Mcf)...................................       1.82       1.63       1.45         1.59          1.81           1.88
COSTS PER BOE:
  Production costs, including severance taxes
   (2)............................................  $    5.59  $    3.94  $    5.91    $    6.60     $    5.98      $    6.45
  Depreciation, depletion and amortization........       2.93       3.09       3.48         3.51          3.25           3.25
</TABLE>
 
- ------------------------------
(1)  Gives effect to  the 1995 Acquisition  and the 1996  Acquisition as if such
    transactions had occurred as of January 1, 1995.
 
(2) Production costs per BOE  in 1995 and for the  three months ended March  31,
    1996  were unusually high  as a result of  relatively high workover expenses
    with respect to properties  acquired in the 1995  Acquisition which did  not
    produce   related  production  improvements  until  subsequent  periods.  In
    addition, the Company expended approximately $1.6 million during 1995 in one
    field in  the Permian  Basin primarily  for plugging  wells to  comply  with
    applicable regulatory requirements.
 
                                       8
<PAGE>
                                  RISK FACTORS
 
    This  Prospectus  contains  certain  forward-looking  statements  within the
meaning of Section  27A of the  Securities Act of  1933 and Section  21E of  the
Securities  Exchange  Act  of  1934.  These  statements  include,  among others,
statements regarding  oil  and gas  reserves,  future drilling  and  operations,
future production of oil and gas and future net cash flows. Actual results could
differ  materially from those  projected in the  forward-looking statements as a
result of various factors, including, without limitation, those set forth  below
and  elsewhere  in  this  Prospectus. Investors  should  carefully  consider the
following  factors,  in  addition  to   other  information  contained  in   this
Prospectus,  in  connection with  an investment  in the  shares of  Common Stock
offered hereby.
 
    SIGNIFICANT LEVERAGE AND DEBT  SERVICE.  As of  March 31, 1996, as  adjusted
for  the 1996 Acquisition,  the Corporate Reorganization,  the Offerings and the
application of  the  net  proceeds  therefrom,  the  Company's  total  debt  and
stockholders'   equity  would  have  been  $100.0  million  and  $35.8  million,
respectively. See "Capitalization." In addition, the Company may currently incur
additional indebtedness under its Credit Facility (as defined under "Description
of  Certain  Indebtedness").  Immediately  following  the  consummation  of  the
Offerings, the Company anticipates that the Credit Facility will afford it $50.0
million  of  available  borrowing capacity,  none  of  which is  expected  to be
outstanding on such date. See "Description of Certain Indebtedness."
 
    The Company's level of indebtedness  will have several important effects  on
its future operations, including (i) a substantial portion of the Company's cash
flow  from  operations must  be  dedicated to  the  payment of  interest  on its
indebtedness and  will  not be  available  for other  purposes,  (ii)  covenants
contained  in the  Credit Facility  and the  Indenture governing  the Notes (the
"Indenture") will require the Company to meet certain financial tests, and other
restrictions may limit its ability to  borrow additional funds or to dispose  of
assets  and may affect  the Company's flexibility in  planning for, and reacting
to, changes in its business, including possible acquisition activities and (iii)
the Company's ability to obtain additional  financing in the future for  working
capital, capital expenditures, acquisitions, general corporate purposes or other
purposes  may  be  impaired. The  Company's  ability  to meet  its  debt service
obligations and to  reduce its  total indebtedness  will be  dependent upon  the
Company's  future  performance,  which  will  be  subject  to  general  economic
conditions and to financial, business and other factors affecting the operations
of the Company, many of which are beyond its control. Based upon the current and
anticipated level of operations,  the Company believes that  its cash flow  from
operations,  together with amounts  available under its  Credit Facility and its
other  sources  of  liquidity,  will   be  adequate  to  meet  its   anticipated
requirements   in   the  foreseeable   future   for  working   capital,  capital
expenditures, interest payments and scheduled  principal payments. There can  be
no  assurance, however,  that the Company's  business will  continue to generate
cash flow at  or above  current levels.  If the  Company is  unable to  generate
sufficient  cash flow from operations in the  future to service its debt, it may
be required to refinance  all or a  portion of its  existing debt including  the
Notes,  or to obtain  additional financing. There  can be no  assurance that any
such refinancing would  be possible or  that any additional  financing could  be
obtained.
 
    RESTRICTIONS IMPOSED BY LENDERS.  The instruments governing the indebtedness
of  the Company and its subsidiaries  impose significant operating and financial
restrictions on the Company. The terms of the Indenture governing the Notes  and
the  Credit  Facility  affect,  and  in  many  respects  significantly  limit or
prohibit, among other  things, the ability  of the Company  to incur  additional
indebtedness,  pay dividends, repay  indebtedness prior to  its stated maturity,
sell assets or engage in mergers or acquisitions. These restrictions could  also
limit the ability of the Company to effect future financing, make needed capital
expenditures,  withstand  a future  downturn in  the  Company's business  or the
economy in  general,  or otherwise  conduct  necessary corporate  activities.  A
failure by the Company to comply with these restrictions could lead to a default
under  the terms of such  indebtedness. In the event  of default, the holders of
such indebtedness could  elect to  declare all  of the  funds borrowed  pursuant
thereto to be due and payable together with accrued and unpaid interest. In such
event,  there can be  no assurance that the  Company would be  able to make such
payments or borrow sufficient  funds from alternative sources  to make any  such
payment.  Even  if  additional financing  could  be  obtained, there  can  be no
assurance that it  would be on  terms that  are favorable or  acceptable to  the
Company.   In   addition,   the   Company's   indebtedness   under   its  Credit
 
                                       9
<PAGE>
Facility is expected to be secured by a substantial portion of the assets of the
Company and its subsidiaries. The pledge of such collateral to existing  lenders
could   impair  the  Company's  ability  to  obtain  additional  financing.  See
"Description of Certain Indebtedness."
 
    POTENTIAL INABILITY  TO FUND  A  CHANGE OF  CONTROL  OFFER.   The  Indenture
governing  the Notes provides that  upon the occurrence of  a Change of Control,
the Company is required  to offer to  repurchase any or  all of the  outstanding
Notes  at  a price  equal to  101%  of the  aggregate principal  amount thereof,
together with accrued  and unpaid  interest, if any,  to the  date of  purchase.
Generally,  a "Change of Control" includes any person or group other than Cadell
S. Liedtke, Michael J. Grella and Henry G. Musselman, the Chairman of the Board,
President and Executive Vice President  of the Company, respectively,  acquiring
50%  or more of the voting securities  of the Company, and certain other events.
If a Change of Control occurs, there is no assurance that the Company will  have
available  funds sufficient to pay for the  Notes tendered for repurchase. If an
offer to  repurchase is  required  to be  made and  the  Company does  not  have
available funds sufficient to pay for Notes tendered for repurchase, an event of
default would occur under the Indenture.
 
    UNCERTAINTY   OF  ESTIMATES   OF  PROVED   RESERVES  AND   FUTURE  NET  CASH
FLOWS.   There are  numerous uncertainties  in estimating  quantities of  proved
reserves  and  in  projecting  future  rates of  production  and  the  timing of
development expenditures,  including  many factors  beyond  the control  of  the
Company.  The  reserve data  set forth  in this  Prospectus are  estimates only.
Reserve estimates are imprecise and should  be expected to change as  additional
information  becomes available. Furthermore, estimates  of oil and gas reserves,
of  necessity,  are  projections  based  on  engineering  data,  and  there  are
uncertainties  inherent  in  the interpretation  of  such  data as  well  as the
projection  of  future  rates  of  production  and  the  timing  of  development
expenditures.   Reserve  engineering  is  a  subjective  process  of  estimating
underground accumulations of oil  and gas that cannot  be exactly measured,  and
the  accuracy of any reserve estimate is  a function of the quality of available
data and of engineering and geological interpretation and judgment. Accordingly,
estimates of the economically recoverable quantities of oil and gas attributable
to any particular group of properties, classifications of such reserves based on
risk of recovery, and estimates of the future net cash flows expected  therefrom
prepared  by different engineers or by the same engineers at different times may
vary substantially. Moreover, there  can be no assurance  that the reserves  set
forth herein will ultimately be produced or that the proved undeveloped reserves
will  be developed within the periods  anticipated. Variances from the estimates
contained herein could  be material. In  addition, the estimates  of future  net
revenues  from proved reserves of the Company  and the present value thereof are
based upon certain assumptions about production levels, prices and costs,  which
may  not be correct. The Company emphasizes  with respect to such estimates that
the discounted future net cash flows  should not be construed as  representative
of  the fair market value of the proved  oil and gas properties belonging to the
Company, because discounted future net cash flows are based upon projected  cash
flows that do not provide for changes in oil and gas prices or for escalation of
expenses  and  capital costs.  The meaningfulness  of  such estimates  is highly
dependent upon  the accuracy  of the  assumptions upon  which they  were  based.
Actual  results may  differ materially  from the  results estimated. Prospective
purchasers of shares of Common Stock  offered hereby are cautioned not to  place
undue reliance on the reserve data included in this Prospectus.
 
    ACQUISITION  RISKS.   The Company's  rapid growth  in recent  years has been
largely the result of acquisitions of producing properties. The Company  expects
to  continue to evaluate and pursue acquisition opportunities available on terms
management considers favorable  to the  Company. The  successful acquisition  of
producing  properties requires an assessment of recoverable reserves, future oil
and gas prices, operating costs,  potential environmental and other  liabilities
and   other  factors  beyond  the  Company's  control.  Such  an  assessment  is
necessarily inexact and its accuracy is inherently uncertain. In connection with
such an assessment, the Company performs  a review of the subject properties  it
believes  to be  generally consistent  with industry  practices. Such  a review,
however, will not reveal all existing or potential problems, nor will it  permit
a  buyer to  become sufficiently  familiar with  the properties  fully to assess
their deficiencies and capabilities. Inspections  may not be performed on  every
well,  and structural and environmental  problems are not necessarily observable
even when an inspection is undertaken. The Company is generally not entitled  to
contractual  indemnification for preclosing liabilities, including environmental
liabilities, and generally acquires  interests in the properties  on an "as  is"
basis.
 
                                       10
<PAGE>
    DRILLING  RISKS.  Drilling involves numerous  risks, including the risk that
no commercially productive oil or gas will be encountered. The cost of drilling,
completing and operating wells is  often uncertain, and drilling operations  may
be  curtailed,  delayed  or cancelled  as  a  result of  a  variety  of factors,
including  unexpected  drilling  conditions,   pressure  or  irregularities   in
formations,  equipment  failures or  accidents,  adverse weather  conditions and
shortages or delays in the delivery of equipment. The Company's future  drilling
activities  may not be successful and, if  unsuccessful, such failure may have a
material adverse  effect  on the  Company's  future results  of  operations  and
financial condition.
 
    OPERATING  HAZARD AND UNINSURED RISKS.  The Company's operations are subject
to  hazards  and  risks  inherent  in  the  drilling  for  and  production   and
transportation  of oil and gas,  including fires, natural disasters, explosions,
encountering formations with abnormal  pressures, blowouts, cratering,  pipeline
ruptures,  and  spills,  any  of  which  can  result  in  loss  of hydrocarbons,
environmental pollution, personal injury or loss  of life, severe damage to  and
destruction  of  properties  of  the  Company  and  others,  and  suspension  of
operations. Although the Company maintains insurance coverage that it  considers
to  be adequate and customary  in the industry, it  is not fully insured against
certain of  these risks,  either  because such  insurance  is not  available  or
because  of high premium costs. The occurrence  of a significant event not fully
covered by  insurance could  have a  material adverse  effect on  the  Company's
financial condition and results of operations.
 
    COMPETITION.   The  Company encounters substantial  competition in acquiring
properties,  marketing  oil  and  gas  and  securing  trained  personnel.   Many
competitors   have   substantially  larger   financial  resources,   staffs  and
facilities. See "Business and Properties -- Competition and Markets."
 
    VOLATILITY OF OIL  AND GAS  PRICES.   The Company's  financial results  and,
therefore,   its  ability  to  service  its   debt,  including  the  Notes,  are
significantly affected  by the  price received  for the  Company's oil  and  gas
production. Historically, the markets for oil and gas have been volatile and may
continue to be volatile in the future. Prices of oil and gas are subject to wide
fluctuations in response to market uncertainty, changes in supply and demand and
a  variety of  additional factors, all  of which  are beyond the  control of the
Company. These factors  include domestic and  foreign political conditions,  the
overall level of supply of and demand for oil and gas, the price of imported oil
and gas, weather conditions, the price and availability of alternative fuels and
overall  economic  conditions.  The  Company's  future  financial  condition and
results of operations will be dependent,  in part, upon the prices received  for
the  Company's  oil and  gas  production, as  well  as the  costs  of acquiring,
finding, developing  and producing  reserves. To  reduce its  exposure to  price
risks  in  the  sale  of  its  oil and  gas,  the  Company  enters  into hedging
arrangements from  time  to time.  Although  the Company  hedges  a  significant
portion  of its production, any substantial or  extended decline in the price of
oil and gas  would have  a material adverse  effect on  the Company's  financial
condition  and  results of  operations,  as well  as  reduce the  amount  of the
Company's oil and gas that could be produced economically. Moreover, if oil  and
gas prices fall materially below their current levels, the availability of funds
and the Company's ability to repay outstanding amounts under its Credit Facility
and  the  Notes  could  be  materially  adversely  affected.  See  "Management's
Discussion and Analysis of Financial Condition and Results of Operations."
 
    DEPENDENCE ON KEY PERSONNEL.  The Company  depends to a large extent on  the
services  of Messrs. Liedtke, Grella and Musselman.  The loss of the services of
any of Messrs. Liedtke, Grella or Musselman could have a material adverse effect
on the Company's operations. Pursuant to  employment agreements which are to  be
effective  upon the consummation  of the Offerings,  Messrs. Liedtke, Grella and
Musselman have agreed  not to compete  with the  Company for a  one year  period
should   they  voluntarily  leave  the  Company's  employment  or  should  their
employment be terminated  for cause. The  Company believes that  its success  is
also  dependent  upon  its ability  to  continue  to employ  and  retain skilled
technical personnel. See "Management."
 
    CONTROL OF THE COMPANY.   If the Offerings  are completed, Messrs.  Liedtke,
Grella  and Musselman will own directly  and indirectly, in the aggregate, 49.2%
of the outstanding Common  Stock (or 46.4%  if the Underwriters'  over-allotment
option  in the Common Stock Offering is exercised in full). Accordingly, Messrs.
Liedtke, Grella and  Musselman will  be able to  exercise significant  influence
over  the  election of  the  directors of  the Company  and  the control  of the
Company's management,  operations and  affairs. The  voting power  held by  such
principal  stockholders and their ability to exercise significant influence over
the election
 
                                       11
<PAGE>
of directors may have the effect  of discouraging certain types of  transactions
involving  an actual  or potential change  of control of  the Company, including
transactions in which  the holders  of Common  Stock might  otherwise receive  a
premium  for  their  shares  over  then  current  market  prices.  See "Security
Ownership of  Certain  Beneficial Owners  and  Management" and  "Description  of
Capital Stock."
 
    FOREIGN  INVESTMENT.   The  Company's investment  in Moldova  involves risks
typically associated  with  investments  in emerging  markets  such  as  foreign
exchange  restrictions  and  currency fluctuations,  foreign  taxation, changing
political  conditions,  foreign   and  domestic  monetary   and  tax   policies,
expropriation,  nationalization, nullification, modification or renegotiation of
contracts, war and civil disturbances and other risks that may limit or  disrupt
markets.  In  addition, if  a  dispute arises  in  its Moldovan  operations, the
Company may be subject  to the exclusive jurisdiction  of foreign courts or  may
not  be  successful in  subjecting foreign  persons to  the jurisdiction  of the
United States.  The  Company attempts  to  conduct its  business  and  financial
affairs  so as  to protect  against political  and economic  risks applicable to
operations in  Moldova,  but there  can  be no  assurance  the Company  will  be
successful in so protecting itself.
 
    GOVERNMENT LAWS AND REGULATIONS.  The Company's operations are affected from
time to time in varying degrees by political developments and federal, state and
local  laws and regulations.  In particular, oil  and gas production, operations
and economics are or have been  significantly affected by price controls,  taxes
and other laws relating to the oil and gas industry, by changes in such laws and
by  changes  in  administrative  regulations.  The  Company  cannot  predict how
existing laws  and regulations  may be  interpreted by  enforcement agencies  or
court  rulings, whether additional laws and  regulations will be adopted, or the
effect such changes may have on its business, financial condition or results  of
operations. See "Business and Properties -- Regulation."
 
    ENVIRONMENTAL  REGULATIONS.  The Company's operations are subject to complex
and constantly changing environmental laws  and regulations adopted by  federal,
state  and local governmental authorities.  The Company believes that compliance
with such laws has had no material adverse effect upon the Company's  operations
to   date  and  that  the  cost  of  such  compliance  has  not  been  material.
Nevertheless, the discharge of oil, gas  or other pollutants into the air,  soil
or  water may give rise to significant liabilities on the part of the Company to
the  government  and  third  parties  and  may  require  the  Company  to  incur
substantial  costs of remediation. Moreover, the Company has agreed to indemnify
sellers of  producing properties  from whom  the Company  has acquired  reserves
against  certain  liabilities  for  environmental  claims  associated  with  the
properties being purchased  by the  Company, including,  without limitation,  in
connection with both the 1995 Acquisition and the 1996 Acquisition. No assurance
can  be  given that  existing environmental  laws  or regulations,  as currently
interpreted or reinterpreted in the future, or future laws or regulations,  will
not  materially  adversely  affect  the  Company's  results  of  operations  and
financial condition or that material indemnity claims will not arise against the
Company with respect to  properties acquired by the  Company. See "Business  and
Properties -- Environmental Matters."
 
    ABSENCE  OF PUBLIC  MARKET FOR THE  COMMON STOCK AND  POSSIBLE VOLATILITY OF
STOCK PRICE.   Prior to  the Common  Stock Offering,  there has  been no  public
market for the Common Stock of the Company and there can be no assurance that an
active  trading  market will  develop  or be  sustained  after the  Common Stock
Offering, or that the market  price of the Common  Stock will not decline  below
the  initial public  offering price.  The initial  public offering  price of the
Common Stock will be determined through negotiations between the Company and the
Underwriters, and may  bear no relationship  to the market  price of the  Common
Stock  after the  Common Stock Offering.  Factors such as  quarterly or cyclical
variations in  the  Company's financial  condition  and results  of  operations,
variations in interest rates, future announcements concerning the Company or its
competitors,  government regulation,  general economic and  other conditions and
developments affecting the oil and gas industry could cause the market price  of
the Common Stock to fluctuate substantially. See "Underwriting."
 
    DILUTION.   Purchasers  of the Common  Stock offered  hereby will experience
immediate and substantial dilution in the pro forma net tangible book value  per
share  of Common Stock from  the initial public offering  price set forth on the
cover of this  Prospectus. Such  dilution to new  investors will  be $11.80  per
share
 
                                       12
<PAGE>
(assuming  an initial public offering price of  $15.00 per share), while the pro
forma net  tangible book  value  of the  shares of  Common  Stock owned  by  the
existing stockholders will increase by $5.79 per share. See "Dilution."
 
    NO  INTENTION  TO  PAY DIVIDENDS.    The  Company intends  to  retain future
earnings for  use  in its  business  and does  not  anticipate paying  any  cash
dividends  in the foreseeable  future. In addition, the  payment of dividends by
the Company is limited and restricted by the Credit Facility and under the terms
of the Indenture governing the Notes. See "-- Restrictions Imposed by  Lenders,"
"Dividend Policy" and "Description of Certain Indebtedness."
 
    ANTI-TAKEOVER  EFFECT OF CERTAIN PROVISIONS  OF THE COMPANY'S CERTIFICATE OF
INCORPORATION AND BYLAWS. The Company's Certificate of Incorporation and  bylaws
provide  that (i) the Company's Directors will be divided into classes, with the
directors of each  class serving staggered  terms of three  years each or  until
their  respective successors  are elected and  qualified, and (ii)  the Board of
Directors may issue serial preferred stock  with such rights and preferences  as
the Board may determine, without stockholder approval. These provisions may have
the  effect,  either  alone  or  in combination,  of  making  more  difficult or
discouraging an acquisition  or potential  acquisition of the  Company which  is
deemed  undesirable by the Board of Directors. See "Description of Capital Stock
- -- Anti-Takeover Provisions."
 
    SHARES ELIGIBLE FOR  FUTURE SALE.   Sales of substantial  amounts of  Common
Stock  on  the public  market after  the Common  Stock Offering  could adversely
affect the market price of the Common Stock. Upon completion of the Common Stock
Offering, the Company  will have a  total of 10,000,000  shares of Common  Stock
outstanding.  Of  these shares,  the 4,000,000  shares  of Common  Stock offered
hereby (4,600,000 shares if the Underwriters' over-allotment option is exercised
in full) will be freely tradeable without restriction or registration under  the
Securities Act of 1933 (the "Securities Act") by persons other than "affiliates"
of  the Company,  as defined under  the Securities Act.  The remaining 6,000,000
shares of Common Stock outstanding will be "restricted securities" as that  term
is  defined by  Rule 144  as promulgated under  the Securities  Act. The Company
currently has  only one  option outstanding  for 75,000  shares. See  "Executive
Compensation and Other Information."
 
    Under  Rule 144  (and subject  to the  conditions thereof,  including volume
limitations), approximately 4,919,992  of the 6,000,000  restricted shares  will
become  eligible for sale 90 days after the Common Stock Offering. All 6,000,000
of the restricted shares are subject to lockup restrictions as described  below.
The  holders of these  shares, which include certain  of the Company's executive
officers and directors and NationsBanc Capital Corp. ("NBCC"), have agreed  that
they  will not, directly or indirectly, offer,  sell, offer to sell, contract to
sell, pledge, grant  any option  to purchase or  otherwise sell  or dispose  (or
announce  any offer, sale, offer of sale, contract to sell, pledge, grant of any
options to purchase or  sale or disposition)  of any shares  of Common Stock  or
other  capital  stock of  the Company,  or any  securities convertible  into, or
exercisable or exchangeable  for, any shares  of Common Stock  or other  capital
stock  of the Company without the prior written consent of Prudential Securities
Incorporated, on behalf of the Underwriters, for  a period of 180 days from  the
date of this Prospectus. After such 180-day period, this restriction will expire
and  shares permitted to be  sold under Rule 144 would  be eligible for sale. In
addition, NBCC has demand registration rights to require the Company to file  up
to  two registration statements to effect  the registration under the Securities
Act of the  shares of Common  Stock held by  such holder, and  the other  majory
stockholders  have  "piggyback"  registration rights,  which  would  permit such
holders to resell such shares without complying with Rule 144. Registration  and
sale  of such shares  could have an adverse  effect on the  trading price of the
Common Stock.  See "Description  of Capital  Stock --  Registration Rights"  and
"Shares Eligible for Future Sale."
 
    Prior  to the Common Stock Offering, there has been no public market for the
Common Stock and no predictions can be made of the effect, if any, that the sale
or availability for sale of shares of  additional Common Stock will have on  the
market  price of the Common Stock. Nevertheless, sales of substantial amounts of
such shares in the public market, or the perception that such sales could occur,
could materially and adversely affect the  market price of the Common Stock  and
could  impair the Company's future ability  to raise capital through an offering
of its equity securities.
 
                                       13
<PAGE>
                                  THE COMPANY
 
GENERAL
 
    The Company  is  an  independent  energy company  that  is  engaged  in  the
acquisition,   exploration,  exploitation   and  development  of   oil  and  gas
properties. The Company's primary operations are in the Permian Basin, the  Gulf
Coast  and the Rocky Mountain regions. The Company recently acquired an interest
in a concession  for the  development of mineral  interests in  the Republic  of
Moldova, in Eastern Europe. The Company also has minor interests in the domestic
gas gathering and transmission business.
 
CORPORATE REORGANIZATION
 
    Costilla  was  incorporated  in Delaware  in  June 1996  to  consolidate and
continue the activities previously conducted by Costilla Energy, L.L.C., a Texas
limited liability company  (the "LLC"),  and its wholly  owned subsidiaries,  to
acquire  the assets  of CSL Management  Corporation ("CSL")  (which owns certain
office equipment  used by  the Company).,  and to  acquire the  stock of  Valley
Gathering  Company ("Valley"). Both CSL and Valley are owned by Messrs. Liedtke,
Grella and Musselman. See "Certain Transactions."
 
    Contemporaneously with the  closings of  the Offerings:  (1) the  redeemable
membership  interests of NBCC in the LLC will be redeemed for $15.4 million; (2)
the LLC  will  be  merged into  Costilla  (the  "Merger") and  an  aggregate  of
6,000,000  shares of Common Stock will be issued to the four members of the LLC;
(3) Costilla will acquire all of the issued and outstanding stock of Valley  and
the  assets of CSL for $0.7 million;  and (4) $4.3 million in distributions will
be made to the members of the LLC, $3.5 million of which, in the case of Messrs.
Liedtke, Grella and  Musselman, will  be provided  to such  persons for  certain
estimated  income tax effects of the  Merger. These transactions are referred to
throughout this Prospectus as the "Corporate Reorganization." As a result of the
Corporate Reorganization, Costilla will have four wholly owned subsidiaries: (i)
Costilla Petroleum  Corporation, a  Texas  corporation ("CPC"),  which  operates
properties  owned by Costilla  and owns minor interests  in the same properties;
(ii) Statewide Minerals Corporation, a Texas corporation ("Statewide"), which is
engaged in the purchase  of small royalty and  mineral interests; (iii)  Valley,
which  owns several small  gas gathering systems, a  small gas processing plant,
certain salt  water disposal  systems  and gas  compressors; and  (iv)  Costilla
Pipeline Company, a Texas corporation ("Pipeline"), which owns a gas pipeline in
Pennsylvania  held for resale. CSL  will be dissolved. Costilla  and CPC are the
sole members  of  two  Texas  limited  liability  companies  through  which  the
Company's Moldovan operations are conducted. Costilla also owns a 45.0% interest
in  a Texas limited liability company which owns and operates a gas pipeline and
associated facilities in Louisiana.
 
    The Company's  executive offices  are located  at 400  West Illinois,  Suite
1000, Midland, Texas, 79701 and its telephone number is (915) 683-3092.
 
                                 NOTES OFFERING
 
    Concurrently  with  the  Common  Stock  Offering,  the  Company  is offering
$100,000,000 of     % Senior Subordinated Notes due 2006. The Notes Offering and
the Common Stock  Offering are  each conditioned  upon the  consummation of  the
other.
 
                                       14
<PAGE>
                                USE OF PROCEEDS
 
    The  net proceeds to the Company from the Common Stock Offering are expected
to be $55.6 million, based upon an  initial public offering price of $15.00  per
share  after  deducting  underwriting discounts  and  commissions  and estimated
offering expenses  to the  Company  ($64.0 million  if the  Underwriters'  over-
allotment  option is exercised). The net proceeds  to the Company from the Notes
Offerings are estimated to be $96.2 million. Approximately $125 million of  such
proceeds,  including all the net proceeds of the Notes Offering, will be used to
repay all of  the existing  senior indebtedness  of the  Company (the  "Existing
Debt")  incurred in connection  with the 1996 Acquisition,  and to refinance its
previous credit facility. The Existing Debt matures in June 1999.  Approximately
$30 million of the Existing Debt currently bears interest at 14.0% per annum and
the  balance currently bears interest at a rate selected by the Company equal to
a base rate  (generally the prime  rate established by  NationsBank, N.A.)  plus
0.75%  or  LIBOR  plus  3.0%.  See  "Description  of  Certain  Indebtedness." In
addition, $20.4 million of the net proceeds will be used to pay certain  amounts
incurred  in  connection  with  the  Corporate  Reorganization,  including $15.4
million to redeem certain membership interests of  NBCC in the LLC prior to  the
Merger,  $0.7 million to acquire  the stock of Valley and  the assets of CSL and
$4.3 million in distributions to the members of the LLC, $3.5 million of  which,
in  the case of Messrs. Liedtke, Grella  and Musselman, will be provided to such
persons for certain  estimated federal  income tax  effects of  the Merger.  See
"Certain  Transactions." The  remaining estimated  net proceeds  of $6.4 million
will be used by the Company for general corporate purposes.
 
    The following is  a description  of sources and  uses of  proceeds from  the
Offerings,  assuming the Underwriters' over-allotment  option in connection with
the Common Stock Offering is not exercised (in millions):
 
<TABLE>
<S>                                                                           <C>
Sources:
  Notes Offering............................................................  $   100.0
  Common Stock Offering.....................................................       60.0
                                                                              ---------
                                                                              $   160.0
                                                                              ---------
                                                                              ---------
Uses:
  Refinance Existing Debt...................................................  $   125.0
  Redeem membership interests...............................................       15.4
  Distributions to individual members to pay estimated income tax liability
   of such members..........................................................        3.5
  Pro rata distribution to remaining member.................................        0.8
  Purchase of stock of Valley and assets of CSL.............................        0.7
  Working capital...........................................................        6.4
  Estimated fees, commissions, underwriting discounts and expenses related
   to the Offerings.........................................................        8.2
                                                                              ---------
                                                                              $   160.0
                                                                              ---------
                                                                              ---------
</TABLE>
 
                                DIVIDEND POLICY
 
    The Company intends to  retain future earnings for  use in its business  and
does  not anticipate declaring  or paying any cash  dividends in the foreseeable
future. The terms of the Credit Facility  are expected to limit or prohibit  the
payment  of dividends by  the Company. In addition,  the Indenture governing the
Notes also contains provisions  restricting the payment  of dividends (or  other
restricted  payments) generally  to (i)  50% of  consolidated net  income of the
Company (less 100% of losses) for the period commencing the first fiscal quarter
after the closing of  the Offerings to the  most recently ended fiscal  quarter,
plus  (ii) 100% of certain equity sales after the date of the Indenture. Subject
to the restrictions  imposed by  the Company's lenders,  future dividend  policy
will  depend  on  a  number  of  factors,  including  future  earnings,  capital
requirements, the financial condition  and future prospects  of the Company  and
such other factors as the Board of Directors may deem relevant.
 
                                       15
<PAGE>
                                    DILUTION
 
    Purchasers  of Common Stock offered hereby  will experience an immediate and
substantial dilution in the net tangible book value of the Common Stock from the
initial public offering price.  At March 31, 1996,  the net tangible book  value
per  share of  Common Stock of  the Company, on  a pro forma  basis after giving
effect to the issuance of 6,000,000 shares  in the Merger and the redemption  of
certain  membership interests in the LLC was  ($2.59). Such amount does not give
effect to the Offerings  or to the  distributions to members of  the LLC in  the
Corporate  Reorganization.  Net tangible  book  value per  share  represents the
amount of the Company's tangible book value (total book value of tangible assets
less total liabilities) divided  by the total number  of shares of Common  Stock
outstanding.  After giving effect  to the receipt of  $55.6 million of estimated
proceeds from the Common Stock Offering, the issuance of the Notes in the  Notes
Offering  and the completion  of the Corporate  Reorganization, the net tangible
book value of the  Common Stock outstanding  at March 31,  1996 would have  been
$32.0  million or  $3.20 per  share, representing  an immediate  increase in net
tangible book value of approximately $5.79 per share to current stockholders and
an immediate dilution of  $11.80 per share (the  difference between the  assumed
initial  public offering price and  the net tangible book  value per share after
the Offerings) to persons purchasing Common Stock at the assumed initial  public
offering price. The following table illustrates such per share dilution:
 
<TABLE>
<S>                                                           <C>        <C>
Assumed public offering price...............................             $   15.00
  Net tangible book value before Offerings..................  $   (2.59)
  Increase in net tangible book value attributable to sale
   of Common Stock in the Common Stock Offering.............       5.79
                                                              ---------
Net tangible book value after giving effect to the
 Offerings..................................................                  3.20
                                                                         ---------
Dilution in net tangible book value to new investors........             $   11.80
                                                                         ---------
                                                                         ---------
</TABLE>
 
    Messrs.  Liedtke,  Grella and  Musselman  will receive  4,919,992  shares of
Common Stock in the Corporate Reorganization. These shares of Common Stock  will
be  issued to such persons in exchange  for the membership interests in the LLC.
The effective  cash  cost  of  these  shares  to  Messrs.  Liedtke,  Grella  and
Musselman,  on a  per share  basis, is not  significant. In  February 1995, upon
formation of the LLC, NBCC contributed $10,000,000 in cash in exchange for a 30%
membership interest in the LLC. Forty  percent of such interest was  immediately
redeemable  for $10,000,000 plus a premium. Therefore, the effective cost of the
1,080,008 shares  of  Common Stock  to  be received  by  NBCC in  the  Corporate
Reorganization is deemed to be zero.
 
                                       16
<PAGE>
                                 CAPITALIZATION
 
    The  following table sets forth the  unaudited capitalization of the Company
as of March 31,  1996, on an historical  basis and on a  pro forma basis  giving
effect  to the 1996 Acquisition, the  Corporate Reorganization and the Offerings
and the application of the net  proceeds therefrom, as if such transactions  had
been consummated as of March 31, 1996, assuming an initial public offering price
for  the Common  Stock in  the Common  Stock Offering  of $15.00  per share. The
following table should be  read in conjunction  with the Consolidated  Financial
Statements  of the LLC, the unaudited  Pro Forma Condensed Financial Statements,
the related  notes,  and  the  other information  contained  elsewhere  in  this
Prospectus,  including the information set forth in "Management's Discussion and
Analysis  of  Financial  Condition  and  Results  of  Operations."  For  further
information regarding the terms of the long-term debt reflected in the following
table,  see "Description of Certain Indebtedness" and  Note 7 and Note 12 of the
Notes to Consolidated Financial Statements.
 
<TABLE>
<CAPTION>
                                                                                                 MARCH 31, 1996
                                                                                            ------------------------
                                                                                            HISTORICAL    PRO FORMA
                                                                                            -----------  -----------
                                                                                                 (IN THOUSANDS)
<S>                                                                                         <C>          <C>
Long-term debt:
  Existing debt...........................................................................   $  74,494    $      --
  Credit Facility.........................................................................          --           --
     % Senior Subordinated Notes due 2006.................................................          --      100,000
                                                                                            -----------  -----------
Total long-term debt......................................................................      74,494      100,000
                                                                                            -----------  -----------
Redeemable members' capital...............................................................      11,678           --
                                                                                            -----------  -----------
Members' capital and stockholders' equity:
  Members' capital........................................................................      (7,535)          --
  Preferred stock, $.10 par value (3,000,000 shares authorized; no shares issued or
   outstanding)...........................................................................          --           --
  Common Stock, $.10 par value (20,000,000 shares authorized; no shares outstanding
   actual, 10,000,000 shares outstanding pro forma).......................................          --        1,000
  Paid-in capital.........................................................................          --       34,843
                                                                                            -----------  -----------
Total members' capital and stockholders' equity...........................................     ( 7,535)      35,843
                                                                                            -----------  -----------
Total capitalization......................................................................   $  78,637    $ 135,843
                                                                                            -----------  -----------
                                                                                            -----------  -----------
</TABLE>
 
                                       17
<PAGE>
                    PRO FORMA CONDENSED FINANCIAL STATEMENTS
 
    The  unaudited Pro Forma Condensed Financial  Statements of the Company have
been prepared to give effect to  the 1995 Acquisition and the 1996  Acquisition,
the  Corporate  Reorganization, and  the Offerings  and  the application  of the
estimated net proceeds  therefrom as  if such  transactions (to  the extent  not
already  reflected) had taken  place on March  31, 1996 for  purposes of the Pro
Forma Condensed Balance  Sheet and  as if the  transactions had  taken place  on
January  1,  1995  for  purposes  of  the  Pro  Forma  Condensed  Statements  of
Operations. The Pro Forma Condensed Financial Statements of the Company are  not
necessarily  indicative of  the results for  the periods presented  had the 1995
Acquisition and  the 1996  Acquisition, the  Corporate Reorganization,  and  the
Offerings  and the  application of  the estimated  net proceeds  therefrom taken
place on January  1, 1995. In  addition, future results  may vary  significantly
from  the results  reflected in the  accompanying Pro  Forma Condensed Financial
Statements because of normal production declines, changes in product prices, and
the success  of  future  exploration and  development  activities,  among  other
factors.  This information should  be read in  conjunction with the Consolidated
Financial Statements  of  Costilla  Energy, L.L.C.  and  subsidiaries,  and  the
Statements  of  Revenues  and  Direct Operating  Expenses  with  respect  to the
properties acquired  in  the 1995  Acquisition  and the  1996  Acquisition,  all
included elsewhere herein.
 
                                       18
<PAGE>
                             COSTILLA ENERGY, INC.
 
                 PRO FORMA CONDENSED BALANCE SHEET -- UNAUDITED
 
                                 MARCH 31, 1996
 
                                 (IN THOUSANDS)
<TABLE>
<CAPTION>
                                                                                                                      PRO FORMA
                                                                                        PRE OFFERING    PRO FORMA     COSTILLA
                                                                           PRO FORMA      COSTILLA       OFFERING      ENERGY,
                        ASSETS                          COSTILLA L.L.C.   ADJUSTMENTS      L.L.C.      ADJUSTMENTS      INC.
- ------------------------------------------------------  ---------------  -------------  -------------  ------------  -----------
<S>                                                     <C>              <C>            <C>            <C>           <C>
Current assets:
  Cash and cash equivalents...........................     $   2,760      $    (700)(3)   $   2,060     $  (4,259)(4)  $  13,498
                                                                                                          151,800(5)
                                                                                                         (136,103)(6)
  Restricted cash.....................................           250                            250                         250
  Accounts receivable.................................         7,584                          7,584                       7,584
  Prepaid and other current assets....................           800                            800                         800
                                                             -------                    -------------                -----------
      Total current assets............................        11,394                         10,694                      22,132
Oil and gas properties, using the successful efforts
 method of accounting:
  Proved properties...................................        83,965         40,500(1)      124,465                     124,465
  Unproved properties.................................         3,580                          3,580                       3,580
  Accumulated depreciation, depletion and
   amortization.......................................       (11,281)                       (11,281)                    (11,281)
                                                             -------                    -------------                -----------
                                                              76,264                        116,764                     116,764
Other property and equipment, net.....................         1,024            700(3)        1,724                       1,724
Deferred charges (Note 2).............................         1,658          3,650(1)        3,650         3,813(5)      3,813
                                                                             (1,658)(2)                    (3,650)(6)
Note receivable -- affiliate..........................           684                            684                         684
                                                             -------                    -------------                -----------
                                                           $  91,024                      $ 133,516                   $ 145,117
                                                             -------                    -------------                -----------
                                                             -------                    -------------                -----------
 
<CAPTION>
 LIABILITIES, REDEEMABLE MEMBERS' CAPITAL AND EQUITY
- ------------------------------------------------------
<S>                                                     <C>              <C>            <C>            <C>           <C>
Current liabilities:
  Trade accounts payable..............................     $   6,190      $  (3,113)(1)   $   3,077                   $   3,077
  Undistributed revenue...............................         1,026                          1,026                       1,026
  Other current liabilities...........................         2,074                          2,074                       2,074
                                                             -------                    -------------                -----------
      Total current liabilities.......................         9,290                          6,177                       6,177
Long-term debt, less current maturities...............        74,494         47,263(1)      121,757     $ 100,000(5)    100,000
                                                                                                         (121,757)(6)
Deferred income.......................................         3,097                          3,097                       3,097
                                                             -------                    -------------                -----------
      Total liabilities...............................        86,881                        131,031                     109,274
Redeemable members' capital...........................        11,678                         11,678       (11,678)(6)         --
Members' capital and capital of affiliates............        (7,535)        (1,658)(2)      (9,193)        9,193(4)         --
Stockholders' equity..................................            --                             --        (2,668)(6)     35,843
                                                                                                           (4,259)(4)
                                                                                                           (9,193)(4)
                                                                                                           55,613(5)
                                                                                                           (3,650)(6)
                                                             -------                    -------------                -----------
                                                           $  91,024                      $ 133,516                   $ 145,117
                                                             -------                    -------------                -----------
                                                             -------                    -------------                -----------
</TABLE>
 
 See accompanying notes to unaudited pro forma condensed financial statements.
 
                                       19
<PAGE>
                             COSTILLA ENERGY, INC.
 
            PRO FORMA CONDENSED STATEMENT OF OPERATIONS -- UNAUDITED
 
                          YEAR ENDED DECEMBER 31, 1995
 
                     (IN THOUSANDS, EXCEPT PER SHARE DATA)
<TABLE>
<CAPTION>
                                                                                                    PRE OFFERING     PRO FORMA
                                                              1995         1996        PRO FORMA      COSTILLA       OFFERING
                                          COSTILLA L.L.C.  ACQUISITION  ACQUISITION   ADJUSTMENTS      L.L.C.       ADJUSTMENTS
                                          ---------------  -----------  -----------  -------------  -------------  -------------
<S>                                       <C>              <C>          <C>          <C>            <C>            <C>
Revenues................................     $  21,816      $  10,930    $  19,891                    $  52,637
Expenses:
  Oil and gas production................        10,355          5,473       11,409    $    (300)(3)      26,937
  General and administrative............         3,571             --           --         (172)(3)       4,850
                                                                                          1,451(7)
  Exploration and abandonments..........         1,650            109        1,002                        2,761
  Depreciation, depletion and
   amortization.........................         6,095             --           --          100(3)       14,313
                                                                                          8,118(8)
  Interest..............................         4,454             --           --        9,388(9)       13,842     $  (2,211)(10)
  Other.................................             2             --           --                            2
                                               -------     -----------  -----------                 -------------
                                                26,127          5,582       12,411                       62,705
                                               -------     -----------  -----------                 -------------
Net income (loss) before federal income
 taxes..................................        (4,311)         5,348        7,480                      (10,068)
Provision for federal income taxes......             3             --           --                            3
                                               -------     -----------  -----------                 -------------
Net income (loss).......................     $  (4,314)     $   5,348    $   7,480                    $ (10,071)
                                               -------     -----------  -----------                 -------------
                                               -------     -----------  -----------                 -------------
Net income (loss) per share.............
 
<CAPTION>
                                           PRO FORMA
                                           COSTILLA
                                            ENERGY,
                                             INC.
                                          -----------
<S>                                       <C>
Revenues................................   $  52,637
Expenses:
  Oil and gas production................      26,937
  General and administrative............       4,850
 
  Exploration and abandonments..........       2,761
  Depreciation, depletion and
   amortization.........................      14,313
 
  Interest..............................      11,631
  Other.................................           2
                                          -----------
                                              60,494
                                          -----------
Net income (loss) before federal income
 taxes..................................      (7,857)
Provision for federal income taxes......           3
                                          -----------
Net income (loss).......................   $  (7,860)
                                          -----------
                                          -----------
Net income (loss) per share.............   $   (0.80)
                                          -----------
                                          -----------
</TABLE>
 
 See accompanying notes to unaudited pro forma condensed financial statements.
 
                                       20
<PAGE>
                             COSTILLA ENERGY, INC.
 
            PRO FORMA CONDENSED STATEMENT OF OPERATIONS -- UNAUDITED
 
                       THREE MONTHS ENDED MARCH 31, 1996
 
                     (IN THOUSANDS, EXCEPT PER SHARE DATA)
<TABLE>
<CAPTION>
                                                                                                             PRO FORMA
                                                                1996         PRO FORMA     PRE OFFERING      OFFERING
                                           COSTILLA L.L.C.   ACQUISITION    ADJUSTMENTS   COSTILLA L.L.C.   ADJUSTMENTS
                                           ---------------  -------------  -------------  ---------------  -------------
<S>                                        <C>              <C>            <C>            <C>              <C>
Revenues.................................     $   8,951       $   5,087                      $  14,038
Expenses:
  Oil and gas production.................         3,659           2,699     $     (75)(3)        6,283
  General and administrative.............         1,362                           (43)(3)        1,505
                                                                                  186(7)
  Exploration and abandonments...........           228             247                            475
  Depreciation, depletion and
   amortization..........................         1,986                            25(3)         3,166
                                                                                1,155(8)
  Interest...............................         1,704                         2,330(9)         4,034      $  (1,126)(10)
                                                 ------          ------                        -------
                                                  8,939           2,946                         15,463
                                                 ------          ------                        -------
Net income (loss) before federal income
 taxes...................................            12           2,141                         (1,425)
                                                 ------          ------                        -------
Net income (loss)........................     $      12       $   2,141                      $  (1,425)
                                                 ------          ------                        -------
                                                 ------          ------                        -------
Net income (loss) per share..............
 
<CAPTION>
                                            PRO FORMA
                                            COSTILLA
                                             ENERGY,
                                              INC.
                                           -----------
<S>                                        <C>
Revenues.................................   $  14,038
Expenses:
  Oil and gas production.................       6,283
  General and administrative.............       1,505
 
  Exploration and abandonments...........         475
  Depreciation, depletion and
   amortization..........................       3,166
 
  Interest...............................       2,908
                                           -----------
                                               14,337
                                           -----------
Net income (loss) before federal income
 taxes...................................        (299)
                                           -----------
Net income (loss)........................   $    (299)
                                           -----------
                                           -----------
Net income (loss) per share..............   $   (0.03)
                                           -----------
                                           -----------
</TABLE>
 
 See accompanying notes to unaudited pro forma condensed financial statements.
 
                                       21
<PAGE>
                             COSTILLA ENERGY, INC.
          NOTES TO UNAUDITED PRO FORMA CONDENSED FINANCIAL STATEMENTS
 
NOTE 1. -- BASIS OF PRESENTATION
    The  Pro  Forma  Condensed Financial  Statements  of the  Company  have been
prepared to give effect  to the 1995 Acquisition  and the 1996 Acquisition,  the
Corporate  Reorganization and the Offerings and the application of estimated net
proceeds therefrom, as if  such transactions had taken  place on March 31,  1996
for purposes of the Pro Forma Condensed Balance Sheet (with the exception of the
1995 Acquisition which was previously reflected in the balance sheet of Costilla
Energy,  L.L.C.), and as if each of  the transactions had taken place on January
1, 1995 for purposes  of the Pro Forma  Condensed Statements of Operations.  The
1995 Acquisition and 1996 Acquisition are accounted for by the purchase method.
 
        Costilla  L.L.C.  -- Represents  the  consolidated balance  sheet of
    Costilla Energy, L.L.C. and  subsidiaries as of March  31, 1996 and  the
    related  consolidated  statements  of  operations  for  the  year  ended
    December 31, 1995 and the three months ended March 31, 1996.
 
        1995 Acquisition  -- Represents  the revenues  and direct  operating
    expenses  of the  properties acquired  in the  1995 Acquisition  for the
    period from  January  1,  1995  to  June 12,  1995  (date  of  the  1995
    Acquisition).
 
        1996  Acquisition --  Represents the  revenues and  direct operating
    expenses of the properties acquired in the 1996 Acquisition for the year
    ended December 31, 1995 and the  three months ended March 31, 1996.  The
    1996 Acquisition was completed on June 14, 1996.
 
NOTE 2. -- PRO FORMA ENTRIES
 
    (1)  To record the issuance of  additional long-term debt under the Existing
Debt Facility (as defined under  "Description of Certain Indebtedness"),  funded
on  June 14, 1996 (net of amounts  used to repay indebtedness under the previous
credit agreement),  and to  record the  use of  the net  proceeds for  the  1996
Acquisition,  to  pay  debt  issuance fees  associated  with  the  Existing Debt
approximating $3,650,000 (including amounts which  would be required to be  paid
in September 1996) and to reflect payment of certain trade accounts payable.
 
    (2)  To record  the write-off of  capitalized loan fees  associated with the
previous credit agreement.
 
    (3) To record the acquisition of Valley Gathering Company and CSL Management
Corporation from certain members  of Costilla Energy, L.L.C.  and to record  the
related  additional depreciation and amortization, and  reduction in oil and gas
production and general and administrative expenses.
 
    (4) To  reflect  the  Corporate Reorganization  including  the  transfer  of
members'  and affiliates'  capital to stockholders'  equity; and  to reflect the
distribution of cash to certain members. See "Use of Proceeds."
 
    (5) To  reflect the  issuance of  4,000,000  shares of  Common Stock  at  an
estimated  price of $15.00 per share  for estimated proceeds of $55,613,000, net
of estimated expenses of the Common Stock Offering, and issuance of the Notes at
$100,000,000; and  to  reflect payment  of  related debt  issuance  expenses  of
$3,812,000.
 
    (6)  To  record the  repayment of  the  Existing Debt  and the  write-off of
related debt issuance costs and the repurchase of redeemable members capital for
approximately $14,346,000 from proceeds of the Offerings.
 
    (7) Estimated incremental general and administrative expenses necessary  due
to  estimated  public  reporting  costs  and  increased  personnel  required  to
administer the  properties  acquired in  the  1996 Acquisition  and  to  reflect
incremental  general  and administrative  expenses due  to the  1995 Acquisition
experienced subsequent to June 12, 1995.
 
    (8) To record  estimated incremental  depletion expense  for the  properties
acquired  in the  1995 Acquisition  from January 1,  1995 through  June 12, 1995
(date of  the 1995  Acquisition) and  for the  properties acquired  in the  1996
Acquisition from January 1, 1995 through March 31, 1996.
 
                                       22
<PAGE>
                             COSTILLA ENERGY, INC.
    NOTES TO UNAUDITED PRO FORMA CONDENSED FINANCIAL STATEMENTS (CONTINUED)
 
NOTE 2. -- PRO FORMA ENTRIES (CONTINUED)
    (9)  To adjust  interest expense  to reflect  additional borrowings  for the
properties acquired in  the 1995 Acquisition  from January 1,  1995 to June  12,
1995  (date of the 1995 Acquisition) and for the properties acquired in the 1996
Acquisition for  the period  of January  1,  1995 through  March 31,  1996.  The
adjustment  also reflects  adjusted interest expense  due to  the Existing Debt.
Also included is the amortization of estimated debt issuance costs of $3,650,000
over a three-year period.
 
    (10) To adjust interest  expense to reflect issuance  of the Notes plus  the
amortization of estimated debt issuance costs over 10 years.
 
NOTE 3. -- INCOME TAXES
    Upon  consummation of the  Corporate Reorganization, the  Company intends to
account for income taxes pursuant  to the provisions of  SFAS 109. At March  31,
1996,  the pro forma tax basis of  the Company's assets and liabilities exceeded
the pro forma book  basis by approximately $6,400,000.  The pro forma  temporary
differences  are primarily related to  the differences in book  and tax basis of
oil and gas properties due to the expensing of intangible development costs  for
tax  purposes and other income tax differences arising from the tax treatment of
oil and gas producing activities.
 
NOTE 4. -- NET INCOME (LOSS) PER SHARE
    Net income (loss) per  share is calculated based  on the pro forma  weighted
average  shares  outstanding  during the  respective  periods.  Weighted average
shares reflect the  pro forma issuance  of 1,080,008 shares  of Common Stock  to
NBCC  on February  17, 1995 and  the pro  forma issuance of  4,919,992 shares of
Common Stock to the remaining holders prior to January 1, 1995. In addition, the
issuance of 4,000,000  shares in the  Common Stock Offering  is assumed to  have
taken place on January 1, 1995 and assumes that the Underwriters' over-allotment
option is not exercised.
 
NOTE 5. -- SUPPLEMENTAL OIL AND GAS RESERVE INFORMATION
    The  estimates of  proved oil  and gas  reserves, which  are located  in the
United States, were prepared by  the Company as of  December 31, 1993, 1994  and
1995, and Williamson as of March 31, 1996. Reserves were estimated in accordance
with  guidelines established by the Securities  and Exchange Commission and FASB
which require that  reserve estimates  be prepared under  existing economic  and
operating conditions with no provision for price and cost escalations, except by
contractual  arrangements.  The  Company  has presented  the  pro  forma reserve
estimates utilizing an oil price of $17.79 per Bbl and a gas price of $2.03  per
Mcf  as of December 31, 1995, and an oil price of $20.91 per Bbl and a gas price
of $2.02 per Mcf as  of March 31, 1996. The  pro forma information assumes  that
both  the 1995  Acquisition and  the 1996 Acquisition  took place  on January 1,
1995.
 
OIL AND GAS PRODUCING ACTIVITIES
 
    Oil and gas reserve quantity estimates are subject to numerous uncertainties
inherent in  the  estimation  of  quantities  of  proved  reserves  and  in  the
projection  of  future  rates  of  production  and  the  timing  of  development
expenditures. The accuracy  of such estimates  is a function  of the quality  of
available  data and of  engineering and geological  interpretation and judgment.
Results of subsequent drilling, testing  and production may cause either  upward
or  downward revision of previous estimates.  Further, the volumes considered to
be commercially  recoverable  fluctuate with  changes  in prices  and  operating
costs. The
 
                                       23
<PAGE>
                             COSTILLA ENERGY, INC.
    NOTES TO UNAUDITED PRO FORMA CONDENSED FINANCIAL STATEMENTS (CONTINUED)
 
NOTE 5. -- SUPPLEMENTAL OIL AND GAS RESERVE INFORMATION (CONTINUED)
Company  emphasizes  that reserve  estimates are  inherently imprecise  and that
estimates of  new  discoveries  are  more  imprecise  that  those  of  currently
producing  oil and gas properties. Accordingly,  these estimates are expected to
change as additional information becomes available in the future.
 
<TABLE>
<CAPTION>
                                                                              OIL AND            GAS
                                                                        CONDENSATE (MBBLS)     (MMCF)
                                                                        -------------------  -----------
<S>                                                                     <C>                  <C>
Balance, January 1, 1995..............................................          17,990          115,281
  Revisions of previous estimates.....................................            (570)             425
  Extensions and discoveries..........................................             605            8,922
  Production..........................................................          (2,085)         (11,984)
                                                                               -------       -----------
Balance, December 31, 1995............................................          15,940          112,644
  Revisions of previous estimates.....................................             436            2,614
  Extensions and discoveries..........................................             592              296
  Production..........................................................            (492)          (2,634)
                                                                               -------       -----------
Balance, March 31, 1996...............................................          16,476          112,920
                                                                               -------       -----------
                                                                               -------       -----------
Proved Developed Reserves:
  December 31, 1995...................................................          13,235           87,345
  March 31, 1996......................................................          13,552           84,369
</TABLE>
 
STANDARDIZED MEASURE OF DISCOUNTED FUTURE NET CASH FLOWS RELATING TO PROVED OIL
AND GAS RESERVES
 
    The standardized measure of discounted future net cash flows is computed  by
applying  period-end prices of oil and  gas (with consideration of price changes
only to the extent provided by contractual arrangements) to the estimated future
production of proved oil  and gas reserves less  estimated future production  of
proved  oil  and  gas  reserves less  estimated  future  expenditures  (based on
period-end costs)  to  be  incurred  in  developing  and  producing  the  proved
reserves,  less  estimated  future  income  tax  expenses  (based  on period-end
statutory tax rates, with consideration of future tax rates already  legislated)
to  be  incurred on  pretax  net cash  flows less  tax  basis of  properties and
available credits, and  assuming continuation of  existing economic  conditions.
The  estimated future net cash flows are then discounted using a rate of 10% per
year to reflect the estimated timing of the future cash flows.
 
    Discounted future  cash  flow  estimates  like those  shown  below  are  not
intended  to represent estimates  of the fair  value of oil  and gas properties.
Estimates of  fair value  should also  consider probable  reserves,  anticipated
future oil and gas prices, interest rates, changes in development and production
costs  and risks associated  with future production. Because  of these and other
considerations, any  estimate  of  fair  value  is  necessarily  subjective  and
imprecise.
 
<TABLE>
<CAPTION>
                                                                           DECEMBER 31,    MARCH 31,
                                                                               1995           1996
                                                                           ------------  --------------
                                                                                  (IN THOUSANDS)
<S>                                                                        <C>           <C>
Future cash flows........................................................   $  512,363    $    572,425
Future costs:
  Production.............................................................     (239,388)       (253,347)
  Development............................................................      (20,907)        (22,076)
                                                                           ------------  --------------
Future net cash flows....................................................      252,068         297,002
10% annual discount for estimated timing of cash flows...................      (98,695)       (117,475)
                                                                           ------------  --------------
Discounted future net cash flows.........................................      153,373         179,527
Future income taxes......................................................      (12,739)        (22,302)
                                                                           ------------  --------------
Standardized measure of discounted net cash flows........................   $  140,634    $    157,225
                                                                           ------------  --------------
                                                                           ------------  --------------
</TABLE>
 
                                       24
<PAGE>
                             COSTILLA ENERGY, INC.
    NOTES TO UNAUDITED PRO FORMA CONDENSED FINANCIAL STATEMENTS (CONTINUED)
 
NOTE 5. -- SUPPLEMENTAL OIL AND GAS RESERVE INFORMATION (CONTINUED)
Changes in Standardized Measure of Discounted Future Net Cash Flows From Proved
Reserves:
 
<TABLE>
<CAPTION>
                                                                           YEAR ENDED    THREE MONTHS
                                                                          DECEMBER 31,  ENDED MARCH 31,
                                                                              1995           1996
                                                                          ------------  ---------------
                                                                                 (IN THOUSANDS)
<S>                                                                       <C>           <C>
Increase (decrease):
  Extensions and discoveries and improved recovery, net of future
   production and development costs.....................................   $    9,598     $     6,002
  Accretion of discount.................................................       14,147           3,516
  Net change in sales prices, net of production costs...................        2,992          20,807
  Changes in estimated future development costs.........................       (1,651)           (238)
  Revisions of quantity estimates.......................................       (2,392)          4,694
  Net change in income taxes............................................        1,633          (9,563)
  Sales, net of production costs........................................      (27,055)         (7,264)
  Changes of production rates (timing) and other........................        1,893          (1,363)
                                                                          ------------  ---------------
    Net increase (decrease).............................................         (835)         16,591
Standardized measure of discounted future net cash flows:
  Beginning of period...................................................      141,469         140,634
                                                                          ------------  ---------------
  End of period.........................................................   $  140,634     $   157,225
                                                                          ------------  ---------------
                                                                          ------------  ---------------
</TABLE>
 
                                       25
<PAGE>
                         SELECTED FINANCIAL INFORMATION
 
    The  following table sets forth selected  financial data of Costilla Energy,
L.L.C. See  "Management's Discussion  and Analysis  of Financial  Condition  and
Results of Operations." The historical information should be read in conjunction
with  the  Consolidated  Financial  Statements and  the  notes  thereto included
elsewhere in  this  Prospectus.  Costilla Energy,  L.L.C.  acquired  significant
producing  oil  and gas  properties in  certain of  the periods  presented which
affect the comparability of the historical financial and operating  information.
The  historical results are  not necessarily indicative  of the Company's future
operations or financial results.
 
<TABLE>
<CAPTION>
                                                                                                        THREE MONTHS ENDED
                                                               YEAR ENDED DECEMBER 31,                      MARCH 31,
                                                -----------------------------------------------------  --------------------
                                                  1991       1992       1993       1994       1995       1995       1996
                                                ---------  ---------  ---------  ---------  ---------  ---------  ---------
                                                                       (IN THOUSANDS, EXCEPT RATIOS)
<S>                                             <C>        <C>        <C>        <C>        <C>        <C>        <C>
STATEMENT OF OPERATIONS DATA:
  Operating revenues..........................  $   1,623  $   2,364  $   4,231  $   7,637  $  21,693  $   2,177  $   8,833
  Total revenues..............................      2,134      2,887      4,397      7,836     21,816      2,180      8,951
  Expenses:
    Oil and gas production....................        769      1,340      1,688      2,351     10,355        896      3,659
    General and administrative................        354        388        952      1,184      3,571        459      1,362
    Exploration and abandonments..............        106          4        218        793      1,650      1,007        228
    Depreciation, depletion and
     amortization.............................        494        404        884      1,847      6,095        462      1,986
    Interest..................................        179        365        605      1,458      4,454        407      1,704
    Other.....................................         --         --         --         --          2         --         --
                                                ---------  ---------  ---------  ---------  ---------  ---------  ---------
  Net income (loss) before income taxes.......        232        386         50        203     (4,311)    (1,051)        12
  Net income (loss)...........................        234        368         73        163     (4,314)    (1,051)        12
STATEMENT OF CASH FLOWS DATA:
  Net cash provided by (used in):
    Operating activities......................  $     276  $     140  $     322  $   1,527  $   6,366  $  (1,827) $   2,276
    Investing activities......................     (2,659)    (1,432)    (6,731)   (12,146)   (62,467)    (1,389)    (5,132)
    Financing activities......................      2,440      1,450      6,315     10,618     58,830      3,272      3,000
OTHER FINANCIAL DATA:
  Capital expenditures........................  $   3,092  $   3,720  $   6,862  $  11,868  $  62,220  $   1,389  $   5,132
  Distributions to members....................         --         --        456        961         55         55         --
  EBITDA (1)..................................      1,011      1,159      1,757      4,301      7,888        825      3,930
  EBITDA/Interest expense (2).................        5.6x       3.2x       2.9x       2.9x       1.8x       2.0x       2.3x
  Ratio of earnings to fixed charges (3)......        1.3        1.5        1.0        1.1         --         --        1.0
BALANCE SHEET DATA (AS OF PERIOD END):
  Working capital.............................  $    (580) $     185  $   1,612  $   1,081  $   2,496         --  $   2,104
  Total assets................................      4,602      6,675     13,365     24,904     87,367         --     91,024
  Total debt..................................      2,870      5,304     12,006     23,591     71,494         --     74,494
  Redeemable members' capital.................         --         --         --         --     11,320         --     11,678
  Members' capital............................        504        434         51       (747)    (7,189)        --     (7,535)
</TABLE>
 
- ------------------------------
(1) EBITDA is presented because of its wide acceptance as a financial  indicator
    as  to a company's  ability to service  or incur debt.  EBITDA should not be
    considered as  an alternative  to earnings  (loss) as  an indicator  of  the
    Company's financial performance or to cash flow as a measure of liquidity.
 
(2)  Calculated  by  dividing  EBITDA by  interest.  Interest  includes interest
    expense accrued and amortization of deferred financing costs.
 
(3) For  purposes  of  calculating  the ratio  of  earnings  to  fixed  charges,
    "earnings"  are net income (loss) plus income taxes and fixed charges. Fixed
    charges are comprised of interest on indebtedness, amortization of  deferred
    financing costs, and that portion of operating lease expense which is deemed
    to  be representative of  an interest factor.  Earnings were insufficient to
    cover fixed charges by $4,311,000, and $1,051,000 for the historical periods
    ended December 31, 1995 and March 31, 1995, respectively.
 
                                       26
<PAGE>
          MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION
                           AND RESULTS OF OPERATIONS
 
GENERAL
 
    Costilla  is  an  independent  energy company  engaged  in  the exploration,
acquisition and development of oil and gas properties. The Company's predecessor
began operating  in 1988  and through  mid-1995 had  grown primarily  through  a
series  of small acquisitions of oil and  gas properties and the exploitation of
those properties. In June 1995, Costilla consummated the 1995 Acquisition for  a
purchase  price  of approximately  $46.6  million, and  in  June 1996,  the 1996
Acquisition was consummated for a purchase price of approximately $42.5 million.
 
    To date, the Company has achieved its high rate of growth primarily  through
acquisitions.  This has impacted  its reported financial results  in a number of
ways. Properties sold by others  frequently have not received focused  attention
prior  to sale. After  acquisition, certain of  these properties are  in need of
maintenance,  workovers,   recompletions  and   other  remedial   activity   not
constituting  capital expenditures, which substantially increase lease operating
expenses. The increased production and revenue resulting from these expenditures
is predominately realized  in periods subsequent  to the period  of expense.  In
addition,  the rapid growth of the Company has required it to develop operating,
accounting and administrative personnel compatible with its increased size.  The
Company  believes it has  now achieved a  sufficient size to  expand its reserve
base without a corresponding increase in its general and administrative expense.
The Company also believes it now has a sufficient inventory of prospects and the
professional staff necessary to  follow a more  balanced program of  exploration
and exploitation activities to complement its acquisition efforts.
 
    Costilla's  strategy is to increase its oil and gas reserves, production and
cash flow  from operations  through  a two-pronged  approach which  combines  an
active  exploration  program with  the  acquisition and  exploitation  of proved
reserves. In  addition,  Costilla  continues  to  evaluate  the  acquisition  of
undeveloped   acreage  for  its  exploration   efforts.  Costilla  has  in-house
exploration expertise  using 3-D  seismic technology  to identify  new  drilling
opportunities as well as for the exploitation of acquired properties.
 
    Costilla  has  shown a  significant increase  in its  oil and  gas reserves,
production and  EBITDA, especially  due to  the 1995  Acquisition and  the  1996
Acquisition.  The following table sets forth  certain operating data of Costilla
for the periods presented:
 
<TABLE>
<CAPTION>
                                                                                           THREE MONTHS ENDED
                                                             YEAR ENDED DECEMBER 31,           MARCH 31,
                                                         -------------------------------  --------------------
                                                           1993       1994       1995       1995       1996
                                                         ---------  ---------  ---------  ---------  ---------
<S>                                                      <C>        <C>        <C>        <C>        <C>
OIL AND GAS PRODUCTION:
  Oil (MBbls)..........................................        158        330        950         86        338
  Gas (Mmcf)...........................................        865      1,600      4,806        477      1,643
  MBOE.................................................        302        597      1,751        166        612
AVERAGE SALES PRICES (1):
  Oil (per Bbl)........................................  $   16.93  $   15.25  $   15.53  $   17.82  $   17.32
  Gas (per Mcf)........................................       1.82       1.63       1.45       1.34       1.81
PRODUCTION COST (2):
  Per BOE (3)..........................................  $    5.59  $    3.94  $    5.91  $    5.40  $    5.98
  Per dollar of sales..................................       0.40       0.31       0.48       0.41       0.41
DEPRECIATION, DEPLETION AND AMORTIZATION:
  Per BOE..............................................  $    2.93  $    3.09  $    3.48  $    2.78  $    3.25
  Per dollar of sales..................................       0.21       0.24       0.28       0.21       0.22
</TABLE>
 
- ------------------------
(1) Before deduction of production taxes and net of hedging results.
 
(2) Excludes depreciation, depletion and amortization. Production cost  includes
    lease operating expenses and production and ad valorem taxes, if applicable.
 
                                       27
<PAGE>
(3) Production  costs per BOE in  1995 and for the  three months ended March 31,
    1996 were unusually high  as a result of  relatively high workover  expenses
    with  respect to properties  acquired in the 1995  Acquisition which did not
    produce  related  production  improvement   until  subsequent  periods.   In
    addition, the Company expended approximately $1.6 million during 1995 in one
    field  in  the Permian  Basin primarily  for plugging  wells to  comply with
    applicable regulatory requirements.
 
    Costilla uses the successful  efforts method of accounting  for its oil  and
gas activities. Costs to acquire mineral interests in oil and gas properties, to
drill  and equip exploratory wells that result  in proved reserves, and to drill
and equip development wells  are capitalized. Costs  to drill exploratory  wells
that  do  not result  in proved  reserves,  geological, geophysical  and seismic
costs, and costs  of carrying  and retaining unproved  properties are  expensed.
Capitalized  costs  of  producing  oil  and  gas  properties,  after considering
estimated dismantlement and abandonment costs and estimated salvage values,  are
depreciated  and depleted using the  unit-of-production method. Unproved oil and
gas properties that are individually  significant are periodically reviewed  for
impairment  of value,  and a  loss is  recognized at  the time  of impairment by
providing an impairment allowance. Other unproved properties are amortized based
on the Company's experience of successful drilling and average holding period.
 
    The Company utilizes option contracts to  hedge the effect of price  changes
on  a portion of  its future oil  and gas production.  Premiums paid and amounts
receivable under the option contracts are  amortized and accrued to oil and  gas
sales, respectively. See "Business and Properties -- Risk Management."
 
    The  Company's  predecessors  were classified  as  partnerships  for federal
income tax purposes. Therefore, no income taxes were paid or provided for by the
Company prior to the  Offerings. Future tax amounts,  if any, will be  dependent
upon  several factors,  including but  not limited  to the  Company's results of
operations.
 
RESULTS OF OPERATIONS
 
  THREE MONTHS ENDED MARCH 31, 1996 COMPARED TO THREE MONTHS ENDED MARCH 31,
1995
 
    The Company's total oil  and gas revenues for  the three months ended  March
31,  1996 were  $8,833,000, representing an  increase of  $6,656,000 (306%) over
revenues of $2,177,000  for the  comparable period  in 1995.  This increase  was
primarily  due  to  the  1995  Acquisition  which  accounted  for  approximately
$5,722,000 of the revenue increase.
 
    Oil and gas production was 612 MBOE in the 1996 period compared to 166  MBOE
in the 1995 period. Of the 446 MBOE increase, 380 MBOE was due to the properties
acquired  in the 1995  Acquisition. The remainder  of the increase  was due to a
combination of successful  drilling activities and  the enhancement of  existing
production.
 
    Interest  and other revenues  were $88,000 for the  three months ended March
31, 1996 compared to $3,000 for  the comparable period in 1995, representing  an
increase  of $85,000, which was  comprised of an increase  in interest income of
$21,000 in  1996 due  to increased  funds earning  interest and  $65,000 in  oil
marketing income. Also in the 1996 period, the Company realized gains of $30,000
on  the sale of various properties for  which there were no comparable sales for
the three months ended March 31, 1995.
 
    Oil and gas production costs in  the 1996 period were $3,659,000 ($5.98  per
BOE),  compared to $896,000 in the 1995  period ($5.40 per BOE), representing an
increase of $2,763,000 (308%), due principally to the 1995 Acquisition. On a per
BOE basis, production costs increased $0.58  due primarily to costs incurred  to
exploit  the properties acquired  in the 1995 Acquisition  which did not produce
related production improvement for the full period. In addition, the 1995 period
was negatively affected by operating costs incurred in connection with  plugging
and abandoning certain wells on properties acquired in late 1994.
 
    General and administrative expense for the three months ended March 31, 1996
was  $1,362,000, representing an increase of $903,000 (197%) from the comparable
period in 1995  of $459,000. The  increase is  primarily due to  an increase  in
personnel and related costs necessary to accommodate the increased activities of
the  Company  due  to the  1995  Acquisition  and in  anticipation  of  the 1996
Acquisition.
 
                                       28
<PAGE>
    Exploration and abandonment expense decreased to $228,000 in the 1996 period
compared to $1,007,000  in the 1995  period. The Company  did not incur  seismic
costs for the three months ended March 31, 1996, compared to $467,000 which were
incurred  for  the comparable  period  in 1995.  Dry  hole costs  decreased from
$540,000 to $228,000 for the comparable periods in 1995 and 1996, respectively.
 
    Depreciation, depletion and  amortization expense  for the  1996 period  was
$1,986,000 compared to $462,000 for the 1995 period, representing an increase of
$1,524,000  (330%). During 1996, depreciation, depletion and amortization on oil
and gas production was provided at an average rate of $3.25 per BOE compared  to
$2.78 per BOE for 1995. The increase was due primarily to the 1995 Acquisition.
 
    Interest expense was $1,704,000 in the 1996 period, compared to $407,000 for
the  comparable period in 1995. The  $1,297,000 (319%) increase was attributable
to increased  levels  of  debt  which  the Company  used  to  finance  the  1995
Acquisition.  The average  amounts of  applicable interest-bearing  debt for the
comparable  periods  in  1996  and   1995  were  $71,923,000  and   $19,820,000,
respectively.
 
  YEAR ENDED DECEMBER 31, 1995 COMPARED TO YEAR ENDED DECEMBER 31, 1994
 
    The  Company's  total  oil  and  gas  revenues  for  1995  were $21,693,000,
representing an increase of  $14,056,000 (184%) over  revenues of $7,637,000  in
1994.  This increase was  primarily due to the  1995 Acquisition which accounted
for approximately $12,032,000 of the revenue increase.
 
    Oil and gas production was 1,751 MBOE in  1995 and 597 MBOE in 1994. Of  the
1,154  MBOE increase, 1,099 MBOE was due  to the properties acquired in the 1995
Acquisition.
 
    Interest and other  revenues were $123,000  in 1995 compared  to $87,000  in
1994,  representing  an increase  of $36,000  (41%), which  was comprised  of an
increase in interest income  of $59,000 in  1995 due to  an increased amount  of
funds  earning  interest, partially  offset  by a  decrease  of other  income of
$23,000. In 1994, the Company realized a gain of $112,000 on the sale of various
properties for which there were no comparable gains in 1995.
 
    Oil and  gas production  costs in  1995 were  $10,355,000 ($5.91  per  BOE),
compared  to $2,351,000  in 1994  ($3.94 per  BOE), representing  an increase of
$8,004,000 (340%).  The major  portion  of the  increase  was due  to  increased
production  associated with the 1995  Acquisition. In addition, certain acquired
properties required remedial workovers and other activity immediately  following
acquisition  resulting  in  unusual operating  costs  of  approximately $600,000
during 1995. In  addition, $1,605,000  of operating costs  were incurred  during
1995  primarily  in connection  with plugging  and  abandoning certain  wells to
comply with applicable  regulatory requirements on  properties acquired in  late
1994.
 
    General  and administrative expense for 1995 was $3,571,000, representing an
increase of $2,387,000 (202%) from 1994  expense of $1,184,000. The increase  is
primarily  due  to  an increase  in  personnel  and related  costs  necessary to
accommodate the increased activities of the Company due to the 1995 Acquisition.
 
    Exploration and abandonment expense increased to $1,650,000 in 1995 compared
to $793,000 in 1994. The increase  of $857,000 (108%) was comprised  principally
of $790,000 of seismic costs.
 
    Depreciation,  depletion and  amortization expense  for 1995  was $6,095,000
compared to $1,847,000 for 1994, representing an increase of $4,248,000  (230%).
During  1995, depreciation, depletion and amortization on oil and gas production
was provided at an average rate of $3.48  per BOE compared to $3.09 per BOE  for
1994. The increase was due primarily to the 1995 Acquisition.
 
    Interest  expense was $4,454,000 in 1995 compared to $1,458,000 in 1994. The
$2,996,000 (205%) increase was  attributable to increased  levels of debt  which
the  Company  used  to finance  the  1995  Acquisition. The  average  amounts of
applicable  interest-bearing  debt  in  1995  and  1994  were  $49,972,000   and
$17,632,000, respectively.
 
                                       29
<PAGE>
  YEAR ENDED DECEMBER 31, 1994 COMPARED TO YEAR ENDED DECEMBER 31, 1993
 
    The  Company's  total  oil  and  gas  revenues  for  1994  were  $7,637,000,
representing an  increase of  $3,406,000 (81%)  over revenues  of $4,231,000  in
1993.  The  primary  reason  for  the  increase  in  revenues  was  due  to  two
acquisitions of properties in  1994, one of which  occurred in January 1994  and
the other in October 1994.
 
    Oil  and gas  production was  597 MBOE  in 1994  and 302  MBOE in  1993. The
increase in  production  of 295  MBOE  was  principally due  to  the  properties
acquired during 1994.
 
    Interest  and other  revenues were  $87,000 in  1994 compared  to $56,000 in
1993. The increase of $31,000 was comprised of an increase in interest income of
$26,000 in 1994,  due to  increased funds  earning interest,  and an  additional
$5,000 in other income.
 
    Oil  and  gas production  costs  in 1994  were  $2,351,000 ($3.94  per BOE),
compared to $1,688,000  in 1993  ($5.59 per  BOE), representing  an increase  of
$663,000.  The increase  in production  costs is  primarily attributable  to two
acquisitions in 1994.
 
    In 1994, general and administrative expense was $1,184,000, representing  an
increase of $232,000 (24%) from 1993 expense of $952,000. The increase is due to
an  increase in  personnel and costs  related primarily to  acquisitions made in
1994.
 
    Exploration and abandonment expense increased  to $793,000 in 1994  compared
to  $218,000 in 1993. The increase of $575,000  (264%) was due to an increase in
non-productive wells drilled in 1994 compared to 1993.
 
    Depreciation, depletion  and amortization  expense for  1994 was  $1,847,000
compared  to $884,000  for 1993,  representing an  increase of  $963,000 (109%),
primarily due to increased production. During 1994, depreciation, depletion  and
amortization  expense on oil and gas production  was provided at an average rate
of $3.09 per BOE  compared to $2.93 per  BOE for 1993. The  increase was due  to
increased   drilling  and   development,  and  the   acquisition  of  additional
properties.
 
    Interest expense was $1,458,000  in 1994 compared to  $605,000 in 1993.  The
$853,000 increase was attributable to increased debt levels related primarily to
the  Company's acquisition  of additional  oil and  gas properties  in 1994. The
average amount  of  applicable  interest-bearing  debt  in  1994  and  1993  was
$17,632,000 and $8,258,000, respectively.
 
LIQUIDITY AND CAPITAL RESOURCES
 
  CAPITAL SOURCES
 
    Funding for the Company's business activities has historically been provided
by  bank financings, cash  flow from operations,  private equity sales, property
divestitures  and  joint  ventures  with  industry  participants.  The   Company
completed a $10 million private equity placement in February 1995. Subsequently,
the  1995 Acquisition and the 1996 Acquisition were substantially funded by bank
financings. The Company plans to  finance its continuing operations and  execute
its  business strategy  with cash  flow from  operations, net  proceeds from the
Offerings and borrowings under the Credit Facility.
 
    The  Company  believes  that  cash   flow  from  operations  and   borrowing
availability  under  the  Credit  Facility will  be  sufficient  for anticipated
operating and  capital expenditure  requirements. However,  because future  cash
flows  and the availability  of financing are  subject to a  number of variables
beyond the  Company's control,  there can  be no  assurance that  the  Company's
capital  resources will  be sufficient to  maintain currently  planned levels of
capital expenditures.
 
    While the Company  regularly engages  in discussions  relating to  potential
acquisitions,  the Company has no present agreement, commitment or understanding
with respect to any such acquisition, other than the acquisition of  undeveloped
acreage  and royalty  and overriding royalty  interests in its  normal course of
business. Any future acquisition  may require additional  financing and will  be
dependent upon financing arrangements available at the time.
 
                                       30
<PAGE>
    The  Company  is in  discussion  with several  banks  to provide  the Credit
Facility following the closing of the Offerings. The Company anticipates that it
will have approximately $50.0 million available under the Credit Facility,  none
of which is expected to be outstanding immediately following the Offerings.
 
    Although  certain of  the Company's  costs and  expenses may  be affected by
inflation, inflationary costs have not had a significant effect on the Company's
results of operations.
 
  CAPITAL EXPENDITURES
 
    The Company requires capital primarily for the exploration, development  and
acquisition of oil and gas properties, the repayment of indebtedness and general
working capital needs.
 
    The  following  table  sets  forth  costs incurred  by  the  Company  in its
development,  exploration  and   acquisition  activities   during  the   periods
indicated. The table does not include the 1996 Acquisition which was consummated
in June 1996 for an approximate purchase price of $42.5 million.
 
<TABLE>
<CAPTION>
                                                                                            THREE MONTHS
                                                               YEAR ENDED DECEMBER 31,          ENDED
                                                           -------------------------------    MARCH 31,
                                                             1993       1994       1995         1996
                                                           ---------  ---------  ---------  -------------
                                                                   (IN THOUSANDS)
<S>                                                        <C>        <C>        <C>        <C>
Development costs........................................  $      --  $      --  $     158    $     232
Exploration costs........................................      2,017      2,167      5,627        1,822
Acquisition costs:
  Unproved properties....................................        829      1,232      1,742          677
  Proved properties......................................      4,665      9,649     52,470        2,246
                                                           ---------  ---------  ---------       ------
    Total................................................  $   7,511  $  13,048  $  59,997    $   4,977
                                                           ---------  ---------  ---------       ------
                                                           ---------  ---------  ---------       ------
</TABLE>
 
    The  Company anticipates that costs incurred  for 1996 will be approximately
$64.8 million, of which  approximately $42.5 million was  expended for the  1996
Acquisition,  and approximately  $5.0 million  was expended  for exploration and
development activities during the three months ended March 31, 1996.
 
                                       31
<PAGE>
                            BUSINESS AND PROPERTIES
 
GENERAL
 
    Costilla  is  an  independent  energy company  engaged  in  the exploration,
acquisition and development  of oil  and gas properties.  The Company's  primary
operations  are in  the Permian  Basin, the  Gulf Coast  and the  Rocky Mountain
regions. The Company's strategy focuses on increasing reserves through  targeted
exploration  programs, the exploitation of its existing properties and selective
property acquisitions. In addition, the Company recently acquired an interest in
a concession  for  the development  of  mineral  interests in  the  Republic  of
Moldova, in Eastern Europe. The Company also has minor interests in the domestic
gas gathering and transmission business.
 
    The  Company's  predecessor began  operating in  1988  with the  strategy of
acquiring and exploiting undervalued oil and gas properties, and at December 31,
1992 had net proved reserves  of 4.7 MMBOE. Since  January 1, 1993, the  Company
has  successfully closed seven  transactions for an  aggregate purchase price of
approximately $101  million.  As  of  March 31,  1996,  the  Company  had  total
estimated  net  proved reserves  of 16.5  Mmbbls of  oil and  112.9 Bcf  of gas,
aggregating 35.3  MMBOE, with  a PV-10  Value of  approximately $179.5  million,
assuming  the 1996 Acquisition had occurred at  March 31, 1996. The Company also
has substantial undeveloped  acreage consisting of  205,908 gross (141,384  net)
undeveloped  acres.  The  Company  has  identified  in  excess  of  200 drilling
locations of which 82 are included in its proved reserves.
 
    Costilla  has  in-house  exploration   expertise  which  uses  3-D   seismic
technology  as  a  primary  tool to  identify  drilling  opportunities,  and has
experienced high rates of  success in each  of its first  two major 3-D  seismic
drilling  programs. Since 1994, the Company has  drilled 23 wells based on these
3-D surveys,  20  of  which  have been  productive.  The  Company  has  recently
completed  a third  3-D survey  in Pecos County,  Texas and  intends to commence
drilling on this acreage in  the second half of  1996. Moreover, the Company  is
currently  conducting two additional 3-D surveys. The Company currently plans to
drill 81 wells through 1997 based on its 3-D surveys.
 
    Since  1993,  Costilla  has   generated  significant  growth  in   reserves,
production  and EBITDA. The Company increased its estimated proved reserves from
6.0 MMBOE at December 31,  1993 to 35.3 MMBOE at  March 31, 1996 (pro forma  for
the  1996 Acquisition), representing a compound annual growth rate of 114%. This
reserve growth has been achieved at an average all-in finding cost of $3.49  per
BOE  over such period, a level which the Company believes is lower than industry
averages. Concurrently, the Company increased  its average net daily  production
from  827 BOE for the year  ended December 31, 1993 to  10,703 BOE for the three
months ended March 31, 1996 (pro forma for the 1996 Acquisition), representing a
compound annual growth rate of 195%. EBITDA increased at a 240% compound  annual
growth  rate from $1.8 million for 1993 to $20.8 million for 1995 (pro forma for
the 1995 Acquisition and the 1996 Acquisition).
 
BUSINESS STRATEGY
 
    The Company's strategy is to increase  its oil and gas reserves,  production
and  cash flow from operations through  a two-pronged approach which combines an
active exploration program  using 3-D seismic  and other technological  advances
with the acquisition and exploitation of producing properties. The Company seeks
to  reduce its operating and  commodity risks by holding  a diverse portfolio of
properties. The  Company also  seeks  to manage  the  elements of  its  business
strategy  through the operation of a  significant portion of its properties, the
use of  a disciplined  rate of  return  analysis and  the direct  marketing  and
hedging  of its oil and  gas production. The elements  of the Company's strategy
may be further described as follows:
 
    - EXPLORATION  EFFORTS.     The  Company  uses   extensive  geological   and
      geophysical  analysis  to carefully  focus its  3-D seismic  surveys. This
      focus allows the Company to successfully direct the size and scope of  its
      exploration  program in order  to improve the  likelihood of success while
      managing overall exploration costs. The Company's exploration efforts  are
      concentrated  currently on known  producing regions. The  Company plans to
      drill 26 exploratory wells during the remainder of 1996 and 36 exploratory
      wells in 1997. Capital budgeted for exploration activities is $8.4 million
      for the last nine months of 1996 and $10.8 million for 1997.
 
                                       32
<PAGE>
    - EXPLOITATION ACTIVITIES.    The  Company  is  actively  pursuing  numerous
      exploitation opportunities within its existing properties, including areas
      where  no proved reserves are  currently assigned. Exploitation activities
      currently in  progress  include  a carbon  dioxide  flood,  recompletions,
      workovers,  infill  and  horizontal  drilling  and  a  secondary  recovery
      project. The Company's capital budget for such activities is $8.9  million
      for the last nine months of 1996 and $9.2 million for 1997, which includes
      the  drilling of 17 development wells in  1996 and 13 development wells in
      1997.
 
    - PROPERTY ACQUISITIONS.  The Company seeks to acquire producing  properties
      where  it has identified opportunities to increase production and reserves
      through both  exploitation and  exploration  activities. The  Company  has
      increased  the  value of  its  acquisitions by  aggressively  managing the
      operations of existing proved  properties and by successfully  identifying
      and  developing  previously  unproved reserves  on  acquired  acreage. The
      Company seeks to acquire reserves  which will fit its existing  portfolio,
      are  generally not  being actively  marketed and  where a  negotiated sale
      would be the method of  purchase. The Company does  not rely on major  oil
      company divestitures or property auctions.
 
    - PROPERTY  DIVERSIFICATION.  The  Company holds a portfolio  of oil and gas
      properties located in  the Permian  Basin, the  Gulf Coast  and the  Rocky
      Mountain  regions. The Company believes  that by conducting its activities
      in distinct  regions  it is  able  to  reduce commodity  price  and  other
      operational risks. The Company's Moldovan interest is an extension of this
      strategy  and  can  be  characterized by  low  initial  costs, significant
      reserve potential  and the  availability  of technical  data that  may  be
      further developed by the Company.
 
    - CONTROL  OF  OPERATIONS.   The  Company  prefers  to operate  and  own the
      majority working  interest  in its  properties.  This allows  the  Company
      greater  control over future development, drilling, completing and lifting
      costs and  marketing of  production.  At December  31, 1995,  the  Company
      operated  wells constituting  approximately 65%  of its  total PV-10 Value
      (pro forma for the 1996 Acquisition).
 
SIGNIFICANT ACQUISITIONS
 
    1995 ACQUISITION.  In  a $46.6 million acquisition  completed in June  1995,
the  Company acquired a group  of oil and gas  properties located in the Permian
Basin, Gulf Coast and  Rocky Mountain regions. At  the date of acquisition,  the
net  proved reserves included 6.9 Mmbbls of oil and 40.0 Bcf of gas, aggregating
13.6 MMBOE.  From the  date of  acquisition until  March 31,  1996, the  Company
produced  1.1  MMBOE from  the acquired  properties  and sold  a portion  of the
acquired properties for approximately $3.6 million.  At March 31, 1996, the  net
proved  reserves  of  the remaining  properties  were 13.4  MMBOE.  The acquired
properties also included 103,010 gross (93,786 net) undeveloped acres.
 
    1996 ACQUISITION.  In June 1996, the Company acquired a group of oil and gas
properties located primarily  in the Permian  Basin and Gulf  Coast regions  for
approximately  $42.5  million.  This acquisition  included  properties  with net
proved reserves at  March 31, 1996  of 5.0 Mmbbls  of oil and  33.5 Bcf of  gas,
aggregating  10.6  MMBOE. The  acquired  properties also  included  42,855 gross
(10,172 net) undeveloped acres and a pipeline located in Pennsylvania which  had
an allocated purchase price of $3.5 million.
 
                                       33
<PAGE>
PRINCIPAL PROPERTIES
 
    The  following table  sets forth certain  information, as of  March 31, 1996
(pro forma for the 1996 Acquisition), which relates to the principal oil and gas
properties owned by the Company.
 
<TABLE>
<CAPTION>
                                                                                     PROVED RESERVES
                                                              -------------------------------------------------------------
                                                                                                  TOTAL OIL    PERCENT OF
                                                                GROSS        OIL         GAS     EQUIVALENT     TOTAL OIL
AREA                                                            WELLS      (MBBLS)     (MMCF)      (MBOE)      EQUIVALENT
- ------------------------------------------------------------  ---------  -----------  ---------  -----------  -------------
<S>                                                           <C>        <C>          <C>        <C>          <C>
Permian Basin...............................................      1,890       9,200      55,200      18,400         52.1%
Gulf Coast..................................................        968       2,054      38,440       8,461         24.0
Rocky Mountain..............................................        236       4,526      12,886       6,674         18.9
Other.......................................................        428         696       6,394       1,762          5.0
                                                              ---------  -----------  ---------  -----------       -----
Total.......................................................      3,522      16,476     112,920      35,297        100.0%
                                                              ---------  -----------  ---------  -----------       -----
                                                              ---------  -----------  ---------  -----------       -----
</TABLE>
 
    PERMIAN BASIN.  At  March 31, 1996, 52.1%  of the Company's proved  reserves
were  concentrated in  the Permian Basin,  an approximately  70-county region in
West Texas and Southeast  New Mexico. The Company's  production comes from  well
known  fields such  as the  Spraberry Trend,  Sawyer Canyon,  Goldsmith Unit and
Susan Peak. The  majority of the  Company's producing intervals  in the  Permian
Basin range from 4,500 feet to 9,500 feet in depth.
 
    The  Company has  several exploratory  projects in  the Permian  Basin based
primarily on 3-D seismic surveys. The most significant include:
 
    EDWARDS/MCELROY RANCH PROSPECT, ECTOR AND  CRANE COUNTIES, TEXAS.   Costilla
has  identified 75 drilling  locations on the Company's  9,849 gross (4,334 net)
acres in  this prospect  based on  3-D seismic  data. The  Company  successfully
completed  the Edwards  14-1 well  in the  Strawn formation  in May  1996, which
initially flowed at a rate  of 360 Bbls of  oil per day and  258 Mcf of gas  per
day.  At June 30, 1996, the well was flowing at a rate of 150 Bbls of oil and 85
Mcf of gas  per day.  Six miles  south of the  Edwards 14-1  well, Costilla  has
drilled  the University 30-1  well, which has confirmed  the Strawn and Wolfcamp
trends defined by the Company's extensive approximate 50-square mile 3-D seismic
project  undertaken  jointly  with   Texaco  Exploration  and  Producing,   Inc.
("Texaco").  This well  is currently being  completed. Two  additional wells are
being drilled  on seismic  delineated features  similar to  the initial  Edwards
discovery.  The Company plans to drill 25  wells in this trend through 1997. The
Company's working interest in this prospect is approximately 44%.
 
    Costilla and Texaco are also developing  a Queen Sand field identified  from
the  Edwards/McElroy Ranch seismic program. The  four wells drilled through June
30, 1996 are producing an aggregate of approximately 80 Bbls of oil per day  and
the  Company is in the  process of completing two  additional wells. Drilling of
six wells is anticipated through 1997, with the field ultimately being developed
on a planned  waterflood pattern in  order to  maximize recovery of  the oil  in
place.
 
    MCGYVER-GREEN  ACRES  PROSPECT,  HOWARD  COUNTY,  TEXAS.    The  Company has
identified 41 drilling locations in  this prospect based on information  derived
from approximately 30 square miles of 3-D seismic data that the Company acquired
on  the area in 1994. The  Talbot Fuller well was the  first well drilled by the
Company on this prospect and was completed in the Canyon Lime formation at 8,200
feet in August 1994. Since completion, the well has produced 62,000 Bbls of  oil
and  207 Mmcf of gas, and averaged 77 Bbls of oil per day and 320 Mcf of gas per
day during June  1996. Subsequent to  the first well,  11 additional wells  have
been  drilled on this prospect of which  ten are productive. The Company intends
to drill eight additional wells  during the balance of  1996 on its 9,148  gross
(6,587  net) acres.  The Company's  working interest  in this  prospect averages
approximately 72%.
 
    The following two 3-D programs currently being undertaken by the Company  in
the Permian Basin are expected to provide additional drilling locations:
 
    WILSON  RANCH 3-D PROJECT, PECOS COUNTY, TEXAS.  The Wilson Ranch is located
in northeastern Pecos County,  approximately 10 miles west  of the Yates  field.
The Company recently completed an approximate
 
                                       34
<PAGE>
17-square  mile seismic survey on the project.  A second phase will be initiated
in the first quarter of 1997. The project presents several potential exploration
targets, including the  Queen, San  Andres, Wolfcamp,  Devonian and  Ellenberger
formations,  found at depths ranging  from 1,600 to 8,000  feet. The Company has
agreed to lease 3,750 gross acres on this 50,000 acre ranch. Upon acquiring  the
lease,  the  Company intends  to sell  one-half of  its approximate  75% working
interest to a major oil company. The Company believes that there is  significant
additional potential in this area.
 
    DAVAN  UNIT 3-D PROJECT,  STONEWALL COUNTY, TEXAS.   The Company has another
3-D  seismic   project  under   way   with  Texaco   to  further   develop   the
Company-operated  Davan Unit. The  project involves a  3-D seismic evaluation of
approximately 3,200 gross acres adjacent to a Company-operated waterflood  which
has produced in excess of three Mmbbls of oil.
 
    Two  examples of the  Company's current exploitation  efforts in the Permian
Basin include:
 
    EAST  GOLDSMITH  FIELD  QUEEN  DISCOVERY  AND  C02  PROJECT,  ECTOR  COUNTY,
TEXAS.   The Company owns 3,053 gross (2,073 net) acres in this field located 20
miles northwest of Midland, Texas. Since  its discovery, the field has  produced
in  excess of 17 Mmbbls of oil  from seven formations. The most productive zones
in the East Goldsmith Field have been  the San Andres and Holt formations,  both
of  which have been subject to  secondary recovery by waterflooding. The Company
has been analyzing a  tertiary recovery project in  those formations using  CO2,
and intends to initiate the project in the fourth quarter of 1996. The Company's
working interest in this project averages approximately 87%.
 
    SUSAN PEAK FIELD WORKOVER AND HORIZONTAL DRILLING PROGRAM, TOM GREEN COUNTY,
TEXAS.   The Company recently completed the  first horizontal well in this field
located south of San  Angelo, Texas, in  which it owns  a 100% working  interest
until  payout. Production from this well drilled in the Strawn formation was 110
Bbls of oil per day and 240 Mcf of gas per day on June 30, 1996. Since  February
1996,  with only  two workovers  and the  new horizontal  well, the  Company has
increased Susan Peak production  from approximately 30 Bbls  of oil per day  and
700  Mcf of gas per day  to a current rate of  approximately 200 Bbls of oil per
day and 2,000 Mcf of gas per day. Two possible horizontal drilling locations and
additional workover  candidates remain  on  this 7,461  gross (3,730  net)  acre
lease. The Company's working interest in this project ranges from 50% to 100%.
 
    GULF  COAST.  At March 31, 1996, 24.0% of the Company's proved reserves were
concentrated in the Gulf Coast region.  The Company's production in this  region
primarily  comes from  known formations  such as  Frio, Yegua,  Austin Chalk and
Wilcox.
 
    The Company  plans  to use  its  expertise in  aggressively  developing  3-D
opportunities on the extensive acreage position it holds in the region. Examples
of such exploration projects in progress include:
 
    SEALY  PROSPECT, AUSTIN COUNTY, TEXAS.  The Sealy Field, consisting of 3,534
gross (1,767  net) acres,  was  acquired in  the  1995 Acquisition.  The  Wilcox
formation in this field has produced over 66 Bcf of gas and there are subsurface
indications  of  the presence  of several  fault blocks  that lie  untested. The
Company's working interest in this prospect is 100%.
 
    SOUTHWEST SPEAKS, LAVACA COUNTY, TEXAS.   This project, consisting of  5,078
gross  (2,539 net) acres, was also acquired  in the 1995 Acquisition and is held
by several  shallow Company-operated  wells.  Multiple producing  horizons  from
shallow  depths to below 14,000 feet have produced over 199 Bcf of gas from this
highly faulted field. A recent well was completed in the Rainbow Wilcox sand  on
acreage  adjoining  Costilla's  lease. A  well,  in  which Costilla  holds  a 5%
interest as a result of a farmout, has also been completed on Costilla's  lease.
The  Company's plans  include a  3-D survey  in the  Speaks area.  The Company's
working interest in this prospect is approximately 50%.
 
    BORCHERS FIELD,  LAVACA COUNTY,  TEXAS.   This  field  was acquired  by  the
Company  in  the 1996  Acquisition. The  property  is on  trend with  the Speaks
project and is  also a highly  faulted field providing  opportunity for  further
development. The Borchers field has produced a total of 17.5 Bcf of gas from two
Wilcox  sands. Costilla has a 100% working  interest in this field consisting of
1,321 gross and net acres.
 
                                       35
<PAGE>
    Examples of exploitation activities in this region include:
 
    JOSEY RANCH LEASE,  HARRIS COUNTY,  TEXAS.   Two examples  of the  Company's
production  enhancement  of  Gulf  Coast  properties  were  undertaken  on  this
prospect. When the lease  was acquired in the  1995 Acquisition, production  had
nearly  ceased. Through  a series of  workovers, the Company  has improved daily
production, as of June 30, 1996, to 63 Bbls of oil per day and 73 Mcf of gas per
day. In addition, Costilla has  participated in a 13,000  foot test well on  the
Josey  Ranch lease to test the Wilcox formation. The well was completed in April
1996 and has consistently produced  in excess of 1,000 Mcf  of gas per day.  The
Josey  Ranch lease covers 1,661 gross (649 net) acres, and the Company's working
interest in this prospect is approximately 39%.
 
    PERSONVILLE, LIMESTONE COUNTY, TEXAS.  The Company has recently completed an
11,200 foot Cotton Valley well, with initial production rates of 1.1 Mmcf of gas
per day prior to stimulation. Costilla leases 412 gross (111 net) acres in  this
prospect,  and has identified two additional  drilling locations. The Company is
the operator of this prospect and its working interest is approximately 30%.
 
    AUSTIN CHALK, BRAZOS, BURLESON, FAYETTE  AND LEE COUNTIES, TEXAS.   Costilla
acquired  the majority of the working interest  in nine gross Austin Chalk wells
in the  1995 Acquisition  and an  additional 80  gross Austin  Chalk wells  were
included  in the 1996 Acquisition. The  Company intends to enhance production on
certain of these wells through stimulation and workover activities, and  analyze
further  development potential. Costilla has 30,414  gross (20,985 net) acres in
the  Austin  Chalk  area,  and  its  working  interest  in  this  area  averages
approximately 69%.
 
    ROCKY  MOUNTAIN.  At March 31, 1996,  18.9% of the Company's proved reserves
were concentrated in the  Rocky Mountain region,  which includes Montana,  North
Dakota, Wyoming, Colorado and Utah.
 
    RAYMOND  FIELD, SHERIDAN COUNTY, MONTANA.   Since its discovery in 1972, the
Raymond Field  has  produced  over  five  Mmbbls  of  oil  from  five  different
formations.  Daily production from the field has  increased from 180 Bbls of oil
per day since its acquisition in  June 1995 to 369 Bbls  of oil per day at  June
30, 1996 primarily as a result of the Company's improved operations. The Company
plans  a 3-D program on its  960 gross and net acres  in this field. The Company
owns a 100% working interest in this prospect.
 
    OUTLOOK FIELD, SHERIDAN COUNTY,  MONTANA.  The  Company undertook its  first
Rocky  Mountain 3-D seismic  survey in the  Outlook area to  further develop the
field. Three  drilling locations  were  identified from  the data.  The  Company
anticipates  commencing  an Outlook  test well  in September  1996 that  will be
drilled to 10,500 feet, a depth sufficient to test several different formations.
Costilla leases 5,168 gross (1,292 net) acres in the Outlook prospect, and  owns
an approximate 25% working interest in this prospect.
 
    NATURAL  BUTTES FIELD, UINTAH COUNTY, UTAH.  The Company owns a 100% working
interest in 1,280  gross and net  acres in this  prospect. Development by  prior
owners  was  on 640-acre  spacing  while offset  acreage  has been  developed on
80-acre spacing. Low  gas prices in  the area have  precluded the assignment  of
proved  resources to any  undeveloped acres. As gas  prices improve, the Company
plans to drill additional wells on the prospect.
 
    The Company owns an interest in  significant acreage positions in the  Rocky
Mountain  region which  are operated  by third  parties and  are the  subject of
active exploitation efforts. The most significant property is:
 
    CIRCLE RIDGE FIELD,  FREMONT COUNTY, WYOMING.   The Circle  Ridge Field,  in
which  the  Company has  an  approximate 18%  working  interest, is  operated by
Marathon Oil Company. This field is an approximate 1,100 acre waterflood located
in the Wind River  Basin of Wyoming, approximately  30 miles north of  Riverton,
Wyoming.  There are 97 active  producing wells and 10  active injection wells in
the field.  Production  originates  from the  Phosphoria,  Tensleep  and  Amsden
formations  that are  present at  depths ranging from  500 to  2,000 feet. Since
January 1995,  45 projects  have been  completed in  the field.  These  projects
include  recompletions,  stimulation  treatments and  reactivations,  which have
increased production from 1,469 Bbls
 
                                       36
<PAGE>
of oil per day in January  1995 to a rate of 1,876  Bbls of oil per day for  May
1996.  The operator  has several other  projects scheduled for  the remainder of
1996 and is evaluating  various different methods of  enhanced oil recovery  for
the field.
 
MARKETING ARRANGEMENTS
 
    The  Company utilizes an active marketing program for a portion of its crude
oil production in order to enhance the net price it receives. The Company  sells
its  crude oil production from operated  properties in North Dakota, Montana and
Wyoming, at the  lease level  to an oil  transportation company  for the  posted
price,  plus an agreed upon bonus,  with a corresponding agreement to repurchase
this production at its delivery point (typically, Cushing, Oklahoma) for a price
equal to the then  posted price for  West Texas Intermediate  crude oil less  an
agreed  upon  deduction for  transportation and  quality differentials,  if any,
between the repurchased  crude oil and  West Texas Intermediate  crude oil.  The
Company  then employs  a broker to  resell its crude  oil to end  users (such as
refineries) on  a month-to-month  basis. The  lease level  sales and  repurchase
contracts  are  typically of  six  months duration.  With  respect to  its other
operated oil  production (primarily  located in  Texas), the  Company employs  a
similar  price enhancement strategy, although  the repurchase feature is absent.
Instead, the lease level  purchaser resells the  crude oil to  end users at  the
delivery  point for  the account  of the  Company. The  Company markets  its gas
production at the lease  level pursuant to  month-to-month contracts. No  single
purchaser  of  oil  or gas  accounted  for in  excess  of 10%  of  the Company's
consolidated revenues for the year ended December 31, 1995.
 
RISK MANAGEMENT
 
    The Company typically  employs a  strategy of  purchasing put  options on  a
portion  of its anticipated oil and gas production. This strategy is designed to
protect the  Company from  significant downward  movements in  commodity  prices
while  preserving the benefit  of rising prices. The  Company does not establish
hedges in  excess  of  its  anticipated production.  Upon  consummation  of  the
Offerings,  substantially  all of  the Company's  debt will  be fixed  rate. The
Company's current position with regard to its commodity hedges is as follows:
 
    OIL SALES.   The Company  has purchased "put  options" to  provide a  "floor
price"  for 3,000  Bbls of  oil per day  of its  oil production  for August 1996
through  December  1996.  These  put   options  currently  in  place   represent
approximately  57% of  the Company's  estimated oil  production for  August 1996
through December 1996. The floor price  the Company has an agreement to  receive
is $18.00 per Bbl, irrespective of the prices actually paid by purchasers of the
oil at the lease level.
 
    GAS  SALES.  The Company has purchased  "put options" which provide a "floor
price" for 900,000 Mmbtu's per month of its gas production through October 1996.
The put options currently in place represent approximately 68% of the  Company's
estimated  gas production for  July 1996 through October  1996. The floor prices
with respect to such put options varies from $1.65 to $1.75 per Mmbtu  depending
on the area in which the gas is produced.
 
OIL AND GAS RESERVES
 
    The  Company's estimated total  proved and proved  developed reserves of oil
and gas as of December 31, 1993, 1994 and 1995, and as of March 31, 1996 were as
follows:
 
<TABLE>
<CAPTION>
                                                             AS OF DECEMBER 31,
                                   ----------------------------------------------------------------------        PRO FORMA
                                                                                                                 MARCH 31,
                                            1993                    1994                    1995                  1996 (1)
                                   ----------------------  ----------------------  ----------------------  ----------------------
                                       OIL         GAS         OIL         GAS         OIL         GAS         OIL         GAS
                                     (MBBLS)     (MMCF)      (MBBLS)     (MMCF)      (MBBLS)     (MMCF)      (MBBLS)     (MMCF)
                                   -----------  ---------  -----------  ---------  -----------  ---------  -----------  ---------
<S>                                <C>          <C>        <C>          <C>        <C>          <C>        <C>          <C>
Proved developed producing.......       1,785      13,268       2,632      15,757       8,338      50,542      13,122      76,439
Proved developed non-producing...           0           0           0         583         228       6,851         429       7,930
Proved undeveloped...............         580       8,351       1,377      11,172       2,222      20,759       2,925      28,551
                                        -----   ---------  -----------  ---------  -----------  ---------  -----------  ---------
  Total proved...................       2,365      21,619       4,009      27,512      10,788      78,152      16,476     112,920
                                        -----   ---------  -----------  ---------  -----------  ---------  -----------  ---------
                                        -----   ---------  -----------  ---------  -----------  ---------  -----------  ---------
</TABLE>
 
- ------------------------
(1)  Assumes that the 1996 Acquisition had been consummated at March 31, 1996.
 
                                       37
<PAGE>
    The following table sets forth the future net cash flows from the  Company's
estimated proved reserves:
 
<TABLE>
<CAPTION>
                                                                               DECEMBER 31,             PRO FORMA
                                                                     --------------------------------   MARCH 31,
                                                                       1993       1994        1995      1996 (1)
                                                                     ---------  ---------  ----------  -----------
                                                                                   (IN THOUSANDS)
<S>                                                                  <C>        <C>        <C>         <C>
Future net cash flows before income taxes..........................  $  47,213  $  68,596  $  188,337   $ 297,002
Future net cash flows before income taxes, discounted at 10%.......  $  26,377  $  36,779  $  113,296   $ 179,527
</TABLE>
 
- ------------------------
(1)  Assumes that the 1996 Acquisition had been consummated at March 31, 1996.
 
    The  reserve estimates reflected above for 1993, 1994 and 1995 were prepared
by the Company. The Company's 1995  estimates of gross reserves with respect  to
certain  of the Company's producing properties  were subject to a limited review
by Williamson.  The  pro forma  estimates  for  March 31,  1996,  including  the
properties acquired in the 1996 Acquisition, were prepared by Williamson and are
part  of reports on the Company's oil and gas properties prepared by Williamson,
a summary of which is set forth herein as Appendix A.
 
    The reserve  data  set forth  herein  present estimates  only.  In  general,
estimates of economically recoverable oil and gas reserves and of the future net
revenues therefrom are based upon an number of variable factors and assumptions,
such  as historical production from the  subject properties, the assumed effects
of regulation by governmental agencies and assumptions concerning future oil and
gas prices and future operating costs,  all of which may vary considerably  from
actual  results.  All  such  estimates  are  to  some  degree  speculative,  and
classifications  of  reserves  are  only  attempts  to  define  the  degree   of
speculation   involved.  For  these  reasons,   estimates  of  the  economically
recoverable oil  and  gas  reserves  attributable to  any  particular  group  of
properties,  classifications  of such  reserves based  on  risk of  recovery and
estimates of the future net  revenues expected therefrom, prepared by  different
engineers  or by the same engineers  at different times, may vary substantially.
The Company therefore emphasizes that the actual production, revenues, severance
and excise taxes,  development and  operating expenditures with  respect to  its
reserves  will  likely vary  from such  estimates, and  such variances  could be
material.
 
    Estimates with respect to proved reserves that may be developed and produced
in the future are often based  upon volumetric calculations and upon analogy  to
similar types of reserves rather than actual production history. Estimates based
on  these  methods  are  generally  less reliable  than  those  based  on actual
production history.  Subsequent  evaluation  of the  same  reserves  based  upon
production  history will result in variations,  which may be substantial, in the
estimated reserves.
 
    In accordance with  applicable requirements of  the Securities and  Exchange
Commission (the "Commission"), the estimated discounted future net revenues from
estimated  proved reserves are based  on prices and costs as  of the date of the
estimate unless such prices or costs are contractually determined at such  date.
Actual  future prices and costs may be materially higher or lower. Actual future
net revenues also will be affected by factors such as actual production,  supply
and  demand for oil and natural gas, curtailments or increases in consumption by
natural gas purchasers, changes in governmental regulations or taxation and  the
impact of inflation on costs.
 
                                       38
<PAGE>
EXPLORATION AND DEVELOPMENT ACTIVITIES
 
    The  Company  drilled, or  participated in  the  drilling of,  the following
number of wells during the periods indicated. At March 31, 1996, the Company was
in the process of drilling one gross (0.50  net) well and was in the process  of
completing  three gross (1.32 net) wells as producers which are not reflected in
the following table.
<TABLE>
<CAPTION>
                                                                1993                    1994                    1995
                                                       ----------------------  ----------------------  ----------------------
                                                          GROSS        NET        GROSS        NET        GROSS        NET
                                                       -----------  ---------  -----------  ---------  -----------  ---------
<S>                                                    <C>          <C>        <C>          <C>        <C>          <C>
Exploratory:
  Productive.........................................           3        0.83           9        2.27          10        4.58
  Dry................................................           2        1.06          10        3.73           6        2.57
                                                              ---         ---         ---         ---         ---         ---
    Total............................................           5        1.89          19        6.00          16        7.15
                                                              ---         ---         ---         ---         ---         ---
                                                              ---         ---         ---         ---         ---         ---
Development:
  Productive.........................................          --          --          --          --           1        0.44
  Dry................................................          --          --          --          --          --          --
                                                              ---         ---         ---         ---         ---         ---
    Total............................................          --          --          --          --           1        0.44
                                                              ---         ---         ---         ---         ---         ---
                                                              ---         ---         ---         ---         ---         ---
Total:
  Productive.........................................           3        0.83           9        2.27          11        5.02
  Dry................................................           2        1.06          10        3.73           6        2.57
                                                              ---         ---         ---         ---         ---         ---
    Total............................................           5        1.89          19        6.00          17        7.59
                                                              ---         ---         ---         ---         ---         ---
                                                              ---         ---         ---         ---         ---         ---
 
<CAPTION>
 
                                                         THREE MONTHS ENDED
                                                           MARCH 31, 1996
                                                       ----------------------
                                                          GROSS        NET
                                                       -----------  ---------
<S>                                                    <C>          <C>
Exploratory:
  Productive.........................................           3        2.02
  Dry................................................           1        0.72
                                                              ---         ---
    Total............................................           4        2.74
                                                              ---         ---
                                                              ---         ---
Development:
  Productive.........................................           4        1.98
  Dry................................................          --          --
                                                              ---         ---
    Total............................................           4        1.98
                                                              ---         ---
                                                              ---         ---
Total:
  Productive.........................................           7        4.00
  Dry................................................           1        0.72
                                                              ---         ---
    Total............................................           8        4.72
                                                              ---         ---
                                                              ---         ---
</TABLE>
 
    The Company  does  not  own  any  drilling rigs  and  all  of  its  drilling
activities  are  conducted by  independent  contractors under  standard drilling
contracts.
 
PRODUCTIVE WELL SUMMARY
 
    The following table  sets forth  the Company's  gross and  net interests  in
productive oil and gas wells as of June 30, 1996. Productive wells are producing
wells and wells capable of production.
 
<TABLE>
<CAPTION>
                                                                                                       ACTUAL (1)
                                                                                                  --------------------
                                                                                                    GROSS       NET
                                                                                                  ---------  ---------
<S>                                                                                               <C>        <C>
Oil wells.......................................................................................      2,245     678.54
Gas wells.......................................................................................      1,277     231.11
                                                                                                  ---------  ---------
    Total.......................................................................................      3,522     909.65
                                                                                                  ---------  ---------
                                                                                                  ---------  ---------
</TABLE>
 
- ------------------------
(1) Does not include royalty and overriding royalty interests owned by Statewide
    or  the Company. See "-- Other  Activities -- Minerals Acquisition Program."
    In addition, one well with multiple completions is counted as a single well.
 
ACREAGE
 
    The following table sets forth  certain information regarding the  Company's
developed  and undeveloped  leasehold acreage as  of March 31,  1996. Acreage in
which the Company's interest is limited to royalty, overriding royalty,  mineral
and similar interests (such as all acreage owned by Statewide) is excluded.
 
<TABLE>
<CAPTION>
                                                         DEVELOPED            UNDEVELOPED            TOTAL (1)
                                                    --------------------  --------------------  --------------------
                                                      GROSS       NET       GROSS       NET       GROSS       NET
                                                    ---------  ---------  ---------  ---------  ---------  ---------
<S>                                                 <C>        <C>        <C>        <C>        <C>        <C>
Permian Basin.....................................     27,049     23,489     52,903     42,250     79,951     65,742
Gulf Coast........................................     34,324     29,746     28,457     19,958     62,781     49,703
Rocky Mountain....................................      8,967      8,676     47,510     40,799     56,477     49,453
Other.............................................     13,439     12,492     34,183     28,225     47,623     40,717
                                                    ---------  ---------  ---------  ---------  ---------  ---------
    Total.........................................     83,779     74,403    163,053    131,212    246,832    205,615
</TABLE>
 
                                       39
<PAGE>
- ------------------------
(1) In  the 1996 Acquisition,  the Company acquired  an additional 292,146 gross
    (73,528 net)  developed  acres and  42,855  gross (10,172  net)  undeveloped
    acres.
 
OTHER ACTIVITIES
 
    MOLDOVA  CONCESSION  AGREEMENT.    In July  1995,  the  Republic  of Moldova
(located in Eastern Europe between Romania and the Ukraine) granted a Concession
Agreement to Resource Development Company Limited, L.L.C. ("Redeco"), an  entity
not  affiliated with the Company. The Company has paid Redeco $90,000 and agreed
to bear the  first $2.0 million  of Concession expenses  ($882,000 of which  had
been  expended through  March 31, 1996)  in return  for a 50.0%  interest in the
Concession. After the initial $2.0  million expenditure, Redeco and the  Company
are  responsible for  bearing 50.0%  each of  future expenses.  The Company will
serve as operator  with respect  to all  activities undertaken  pursuant to  the
Concession.  The Concession Agreement covers the  entire country with respect to
oil and gas and other minerals and continues for various time periods  depending
on  the  nature of  the activity  conducted. In  connection with  two previously
producing but now abandoned fields, the Company's exclusive rights continue  for
20  years. The Company's exclusive period to explore throughout the remainder of
Moldova expires in  2005, but  the Company will  maintain exclusive  development
rights  with respect to fields discovered for a period of 20 years from the date
of first  production  from  such  field. The  Company  has  no  fixed  financial
commitments with respect to the Concession.
 
    MINERALS   ACQUISITION  PROGRAM.    Statewide,  a  Company  subsidiary,  was
organized for the purpose  of acquiring overriding  royalty interests and  other
types  of non  cost-bearing mineral interests  underlying producing  oil and gas
fields primarily in Texas. The strategy of such acquisitions is to make  blanket
offers  to holders  of small interests.  From inception through  March 31, 1996,
Statewide  expended  approximately  $2.9  million  in  acquiring  interests   in
approximately  1,400 properties. Through March  31, 1996, Statewide had received
revenues from such interests aggregating approximately $1.2 million, as well  as
proceeds from sales of such interests of approximately $150,000.
 
    GAS  GATHERING AND  TRANSMISSION.   In 1996,  the Company  purchased a 45.0%
membership interest (which reduces to 32.4%  when the Company and certain  other
members  recoup their original  investment) in Republic  Gas Partners, L.L.C., a
Texas  limited  liability  company  ("Republic"),  for  approximately  $800,000.
Republic  owns all  of the  stock of  Mid Louisiana  Gas Company,  Mid Louisiana
Marketing Company and Mid Louisiana Gas Transmission Company (collectively,  the
"Midla  Companies").  The assets  of the  Midla Companies  include 409  miles of
mainly 22 inch pipeline extending from the  Monroe field area south of the  city
of   Baton  Rouge  serving  various  Louisiana  and  Mississippi  municipal  and
industrial customers along its  route. Mid Louisiana  Gas Company's pipeline  is
subject  to  the  jurisdiction  of  the  Federal  Energy  Regulatory  Commission
("FERC").
 
    Valley, a Company  subsidiary, owns  a small gas  gathering system,  several
small  gas plants,  11 salt water  disposal wells  located in each  of its three
principal regions and compressors used in the compression of gas located in  the
Gulf  Coast region. For the year ended December 31, 1995, Valley had revenues of
$553,000 and net income of $264,000, substantially all of which were related  to
transactions with Costilla.
 
    In the 1996 Acquisition, Pipeline, a Company subsidiary, acquired a 120 mile
gas  transportation pipeline in southwestern Pennsylvania for an allocated value
of $3.5 million. The Company regards this asset as non-strategic to its business
activities and is presently marketing the pipeline for sale.
 
COMPETITION AND MARKETS
 
    Competition in all areas of the  Company's operations is intense. Major  and
independent  oil and gas companies  and oil and gas  syndicates actively bid for
desirable oil  and  gas properties,  as  well as  for  the equipment  and  labor
required  to  operate and  develop such  properties. A  number of  the Company's
competitors  have   financial  resources   and  acquisition,   exploration   and
development  budgets that are  substantially greater than  those of the Company,
which  may  adversely  affect  the  Company's  ability  to  compete  with  these
companies.  Many of  the Company's competitors  have been engaged  in the energy
business for a much longer time than the Company. Such companies may be able  to
pay more for productive oil and gas
 
                                       40
<PAGE>
properties  and  exploratory  prospects and  to  define, evaluate,  bid  for and
purchase a  greater  number  of  properties and  prospects  than  the  Company's
financial or human resources permit. The Company's ability to acquire additional
properties  and to  discover reserves  in the  future will  be dependent  on its
ability  to  evaluate   and  select  suitable   properties  and  to   consummate
transactions in a highly competitive environment.
 
    The  market for  oil, gas  and natural gas  liquids produced  by the Company
depends on factors beyond its control, including domestic and foreign  political
conditions,  the overall level of supply of  and demand for oil, gas and natural
gas liquids, the price of imports of oil and gas, weather conditions, the  price
and  availability  of  alternative  fuels, the  proximity  and  capacity  of gas
pipelines and other transportation  facilities and overall economic  conditions.
The  oil and  gas industry  as a  whole also  competes with  other industries in
supplying the  energy  and  fuel  requirements  of  industrial,  commercial  and
individual consumers.
 
REGULATION
 
    The Company's oil and gas exploration, production and related operations are
subject  to extensive  rules and regulations  promulgated by  federal, state and
local agencies. Failure to comply with such rules and regulations can result  in
substantial  penalties.  The  regulatory  burden on  the  oil  and  gas industry
increases the Company's cost  of doing business  and affects its  profitability.
Because  such rules and regulations are frequently amended or reinterpreted, the
Company is unable to predict  the future cost or  impact of complying with  such
laws.
 
    The  State  of Texas  and  many other  states  require permits  for drilling
operations, drilling bonds  and reports concerning  operations and impose  other
requirements  relating to  the exploration and  production of oil  and gas. Such
states also  have  statutes  or  regulations  addressing  conservation  matters,
including  provisions for the unitization or  pooling of oil and gas properties,
the establishment of maximum rates of production from oil and gas wells and  the
regulation  of spacing, plugging and abandonment of such wells. The statutes and
regulations of  certain states  limit  the rate  at which  oil  and gas  can  be
produced from the Company's properties.
 
    The  FERC regulates interstate natural  gas transportation rates and service
conditions, which affect the marketing of  gas produced by the Company, as  well
as  the revenues received by the Company for sales of such production. Since the
mid-1980s, the FERC  has issued a  series of orders,  culminating in Order  Nos.
636,  636-A  and  636-B  ("Order  636"),  that  have  significantly  altered the
marketing  and  transportation  of  gas.   Order  636  mandates  a   fundamental
restructuring of interstate pipeline sales and transportation service, including
the unbundling by interstate pipelines of the sales, transportation, storage and
other  components  of the  city-gate  sales services  such  pipelines previously
performed. One  of the  FERC's purposes  in issuing  the orders  is to  increase
competition within all phases of the gas industry. Order 636 and subsequent FERC
orders  on rehearing have been appealed and are pending judicial review. Because
these orders may  be modified as  a result of  the appeals, it  is difficult  to
predict  the ultimate impact of the orders  on the Company and its gas marketing
efforts. Generally,  Order  636  has eliminated  or  substantially  reduced  the
interstate  pipelines' traditional role  as wholesalers of  natural gas, and has
substantially increased competition and volatility in natural gas markets. While
significant regulatory uncertainty remains, Order 636 may ultimately enhance the
Company's ability to market and transport its gas, although it may also  subject
the  Company to greater competition and  the more restrictive pipeline imbalance
tolerances and greater associated penalties for violation of such tolerances.
 
    Sales of oil and natural  gas liquids by the  Company are not regulated  and
are made at market prices. The price the Company receives from the sale of these
products  is  affected  by the  cost  of  transporting the  products  to market.
Effective as of January  1, 1995, FERC  implemented regulations establishing  an
indexing  system for transportation  rates for oil  pipelines, which, generally,
would  index  such  rates  to  inflation,  subject  to  certain  conditions  and
limitations.  These regulations could increase the  cost of transporting oil and
natural gas liquids by pipeline,  although the most recent adjustment  generally
decreased rates. These regulations are subject to pending petitions for judicial
review.  The Company is not able to  predict with certainty what effect, if any,
these regulations  will  have  on  it,  but,  other  factors  being  equal,  the
regulations  may, over  time, tend  to increase  transportation costs  or reduce
wellhead prices for oil and natural gas liquids.
 
                                       41
<PAGE>
ENVIRONMENTAL MATTERS
 
    Operations of the Company  are subject to  numerous and constantly  changing
federal,  state  and  local  laws and  regulations  governing  the  discharge of
materials  into  the   environment  or  otherwise   relating  to   environmental
protection.  These laws and  regulations may require  the acquisition of certain
permits, restrict  or  prohibit  the  types,  quantities  and  concentration  of
substances that can be released into the environment in connection with drilling
and  production,  restrict or  prohibit  drilling activities  that  could impact
wetlands, endangered or threatened species or other protected natural  resources
and  impose substantial liabilities  for pollution resulting  from the Company's
operations. Such laws  and regulations  may substantially increase  the cost  of
exploring  for, developing or producing oil and gas and may prevent or delay the
commencement or continuation of a given project. In the opinion of the Company's
management, the Company  is in  substantial compliance  with current  applicable
environmental  laws and regulations,  and the cost of  compliance with such laws
and regulations has not been material and is not expected to be material  during
the  next fiscal year. Nevertheless, changes  in existing environmental laws and
regulations or in interpretations thereof could have a significant impact on the
operating costs of the Company, as well as the oil and gas industry in  general.
For  instance, legislation has been proposed in  Congress from time to time that
would reclassify certain oil  and gas production  wastes as "hazardous  wastes,"
which  reclassification would make exploration  and production wastes subject to
much  more  stringent  handling,  disposal  and  clean-up  requirements.   State
initiatives to further regulate the disposal of oil and gas wastes and naturally
occurring  radioactive materials are  also pending in  certain states, including
Texas, and these various initiatives could have a similar impact on the Company.
 
    The Comprehensive Environmental  Response, Compensation,  and Liability  Act
("CERCLA"), also known as the "Superfund" law, imposes liability, without regard
to  fault or the legality of the original conduct, on certain classes of persons
that are  considered  to  have  contributed  to  the  release  of  a  "hazardous
substance"  into the environment. These persons include the owner or operator of
the disposal site  or the  site where the  release occurred  and companies  that
disposed  or arranged for the disposal of  the hazardous substances found at the
site. Persons who are or were  responsible for releases of hazardous  substances
found  at  the site  and persons  who are  or were  responsible for  releases of
hazardous substances under CERCLA may be subject to joint and several  liability
for  the costs of cleaning  up the hazardous substances  that have been released
into the  environment  and for  damages  to natural  resources,  and it  is  not
uncommon  for neighboring landowners and other  third parties to file claims for
person injury and property damage  allegedly caused by the hazardous  substances
released  into  the environment.  The Company  is able  to control  directly the
operation of  only those  wells with  respect  to which  its acts  as  operator.
Notwithstanding the Company's lack of control over wells operated by others, the
failure of the operator to comply with applicable environmental regulations may,
in  certain  circumstances, be  attributed to  the Company.  The Company  has no
material  commitments  for   capital  expenditures  to   comply  with   existing
environmental requirements.
 
EMPLOYEES
 
    At  June 30,  1996, the  Company had  109 full-time  employees. None  of the
Company's employees is subject to a collective bargaining agreement. The Company
considers its relations with its employees to be good.
 
LEGAL PROCEEDINGS
 
    The Company is a defendant or codefendant in minor lawsuits that have arisen
in the ordinary  course of  business. While the  outcome of  the these  lawsuits
cannot  be predicted with certainty, management does  not expect any of these to
have a material adverse effect on the Company's consolidated financial condition
or results of operations.
 
TITLE TO PROPERTIES
 
    The Company  has  obtained  title  opinions  on  substantially  all  of  its
producing  properties  and  believes  that it  has  satisfactory  title  to such
properties in accordance with  standards generally accepted in  the oil and  gas
industry.  As is customary in  the oil and gas  industry, the Company performs a
minimal title  investigation before  acquiring undeveloped  properties. A  title
opinion    is    obtained    prior    to    the    commencement    of   drilling
 
                                       42
<PAGE>
operations on such properties. The Company's properties are subject to customary
royalty interests, liens  incident to  operating agreements,  liens for  current
taxes  and other burdens which the  Company believes do not materially interfere
with the use of or affect the value of such properties. Substantially all of the
Company's oil and gas  properties are mortgaged to  secure borrowings under  the
Company's  Existing Debt  Facility and will  continue to be  mortgaged to secure
borrowings under the Credit Facility. See "Management's Discussion and  Analysis
of  Financial  Conditions and  Results of  Operations  -- Liquidity  and Capital
Resources," and "Description of Certain Indebtedness."
 
OPERATIONAL HAZARDS AND INSURANCE
 
    The Company's operations are  subject to the hazards  and risks inherent  in
drilling  and production  and transportation  of oil  and gas,  including fires,
natural disasters, explosions, encountering formations with abnormal  pressures,
blowouts,  cratering, pipeline ruptures, and spills,  any of which can result in
loss of hydrocarbons, environmental pollution, personal injury or loss of  life,
severe  damage to and destruction  of properties of the  Company and others, and
suspension of operations. See "Risk Factors -- Drilling Risks" and "Risk Factors
- -- Operating Hazards and Uninsured Risks."
 
    The Company maintains insurance  of various types  to cover its  operations.
The  limits provided under its liability policies total $6 million. In addition,
the Company maintains operator's extra expense coverage which provides for care,
custody and control of  all material wells drilled  by the Company as  operator.
The  Company believes that its insurance is adequate and customary for companies
of a similar size  engaged in operations  similar to those  of the Company,  but
losses could occur for uninsurable or uninsured risks or in amounts in excess of
existing  insurance coverage.  The Company's  general policy  is to  only engage
drilling contractors who  provide substantial  insurance coverage  and name  the
Company  as an additional named insured. The occurrence of a significant adverse
event, the risks  of which  are not  fully covered  by insurance,  could have  a
material  adverse effect  on the  Company's financial  condition and  results of
operations. Moreover, no assurances can be  given that the Company will be  able
to maintain adequate insurance in the future at rates it considers reasonable.
 
                                       43
<PAGE>
                                   MANAGEMENT
 
    The  executive officers and directors of the Company following completion of
the Corporate Reorganization are  listed below, together  with a description  of
their experience and certain other information (ages provided are as of June 30,
1996).  Each of the directors serve for  a one year term. Executive officers are
appointed by the Board of Directors.
 
<TABLE>
<CAPTION>
NAME                            AGE       EMPLOYED SINCE                         POSITION WITH COMPANY
- --------------------------      ---      -----------------  ---------------------------------------------------------------
<S>                         <C>          <C>                <C>
Cadell S. Liedtke                   41            1988      Chairman of the Board, Chief Executive Officer and Director
Michael J. Grella                   47            1988      President, Chief Operating Officer and Director
Henry G. Musselman                  42            1992      Executive Vice President and Director
Jerry J. Langdon                    43             n/a      Director
W.D. Kennedy                        76             n/a      Director
Bobby W. Page                       53            1996      Senior Vice President, Treasurer and Chief Financial Officer
Clifford N. Hair, Jr.               49            1992      Vice President -- Land and Secretary
Roger J. Wetz                       47            1992      Vice President -- Exploration (Geology)
Roger A. Freidline                  46            1993      Vice President -- Exploration (Geophysics)
Brian K. Miller                     36            1992      Vice President -- Reservoir Engineering
Sal J. Pagano                       45            1995      Vice President -- Engineering and Operations
Keith Atwood                        42            1992      Vice President -- Field Operations
Celia A. Zinn                       48            1996      Controller
</TABLE>
 
    Cadell S. Liedtke entered the oil and gas business in Midland, Texas in 1977
as an independent landman generating oil and gas prospects in the Permian Basin.
He founded the  Company's predecessor  with Michael J.  Grella in  1988 and  has
served  as managing partner and/or chief  executive officer since that time. Mr.
Liedtke has served  on the  Board of  Directors of  Texas Commerce  Bank-Permian
Basin and has been appointed by Texas Governor George W. Bush to the Oil and Gas
Compact  Commission. Mr.  Liedtke is  a member  of the  All-American Wildcatters
Association,  the  Permian  Basin  Petroleum  Association,  the  Permian   Basin
Landman's Association and the Independent Producer's Association of America. Mr.
Liedtke  graduated from the  University of Texas  at Austin in  1977 with a B.A.
degree in economics.
 
    Michael J. Grella has served as  Chief Operating Officer of the Company  and
its predecessor entities since their formation in 1988. He owned and operated an
independent  oil and gas  company and has  invested in the  oil and gas business
since 1982. Mr. Grella  is a member of  the Permian Basin Petroleum  Association
and  the Independent  Producer's Association of  America. Mr. Grella  has a B.S.
degree in computer science from the University of California.
 
    Henry G.  Musselman began  his oil  and gas  career in  1975 with  Musselman
Petroleum  and Land  Company where  he served as  Vice President  and a Director
until forming Musselman, Owen & King in 1982. For the 10 years until merging his
company into  Costilla's  predecessor  in  1992,  Mr.  Musselman  developed  and
acquired oil and gas properties throughout the Permian Basin. Mr. Musselman is a
member  and prior director of the Independent Producer's Association of America.
Mr. Musselman graduated from the  University of Texas at  Austin in 1975 with  a
B.B.A. degree.
 
    Jerry  J. Langdon has previously held positions with WP Corporation, Houston
Pipeline Company, Texas  Oil &  Gas Corporation  and W.  Wilson Corporation.  In
1980,  Mr. Langdon formed  Texas IntraMark Gas Company,  Inc., an intrastate gas
gathering company engaging in the business of constructing and operating natural
gas gathering, treating and processing  facilities. In 1984, Mr. Langdon  formed
Langdon  &  Associates,  a  natural  gas  consulting  group  advising  petroleum
resource-oriented companies, financial institutions and  law firms on a  variety
of  technical, commercial and regulatory issues.  Mr. Langdon served as a member
of the FERC from 1988 to June  1993. Since leaving the FERC, Mr. Langdon  formed
Republic Gas Corp. to
 
                                       44
<PAGE>
acquire,  construct  and  operate intrastate  natural  gas  pipeline, gathering,
processing, treating and marketing facilities.  Mr. Langdon is the President  of
both  Republic and the  Midla Companies. Mr.  Langdon is a  1975 graduate of the
University of Texas at Austin with a B.S. degree.
 
    W. D. Kennedy  has been  continually involved in  the oil  and gas  business
since  1948. From  1953 until  1980, Mr.  Kennedy was  an executive  officer and
director of C&K Petroleum, Inc., and its predecessor. C&K Petroleum, Inc. was  a
publicly held corporation from 1971 until 1980, when the company was sold for in
excess  of $200 million. Mr.  Kennedy remains an active  investor in the oil and
gas business. Mr. Kennedy is a graduate of the University of Texas, and a member
of the All-American  Wildcatters Association,  a past president  of the  Permian
Basin  Petroleum Association, a  former director of  the Texas Mid-Continent Oil
and Gas Association, and an advisory director of Norwest Bank Texas, Midland.
 
    Bobby W. Page began his oil and gas career with MGF Oil Corporation in 1967,
where he remained until  1988, ultimately serving  as Executive Vice  President,
Chief  Financial Officer and a  member of the Board  of Directors. Following two
years as  a self-employed  financial  consultant, Mr.  Page joined  Alta  Energy
Corporation  in 1990 as Executive Vice  President, Treasurer and Chief Financial
Officer. From  July 1993  until joining  the Company,  Mr. Page  served as  Vice
President, Chief Financial Officer and Secretary of Marcum Natural Gas Services,
Inc.  Mr. Page graduated from the University of Oklahoma with a B.B.A. degree in
accounting in 1965.
 
    Clifford N. Hair, Jr. has served in district and division landman roles,  as
well  as a corporate officer with Texas Gas Exploration Corporation, Samedan Oil
Corporation, Henry Petroleum Corporation and Donald C. Slawson Oil Producer. For
the two  year period  prior to  joining the  Company in  1992, Mr.  Hair was  an
independent  landman involved  in drilling projects  in Texas  and Oklahoma. Mr.
Hair is a Certified Petroleum Landman  and a member of the American  Association
of  Petroleum Landmen  and the Petroleum  Basin Landman's  Association. Mr. Hair
graduated with  honors from  the University  of Houston  in 1971  with a  B.B.A.
degree in accounting.
 
    Roger J. Wetz began his oil and gas career with IMCO Services, a division of
Halliburton,  Inc. in 1974. He held a  variety of geological positions with Gulf
Energy & Minerals Company, TXO Production Corporation and Terra Resources,  Inc.
from  1976 to 1989. From 1989 until joining the Company in 1992, Mr. Wetz was an
independent geologist  generating  prospects  in the  Permian  Basin.  Mr.  Wetz
graduated from St. Mary's University in 1973 with a B.S. degree in geology.
 
    Roger  A.  Freidline began  his industry  career with  Union Oil  Company of
California. From 1976 until  1985, Mr. Freidline  served in various  geophysical
capacities  with Forest  Oil Corporation,  Gifford, Mitchell  and Wisenbaker and
Heritage Resources, Inc. Mr. Freidline was an independent geophysicist from 1985
until joining  the  Company, except  for  a  period of  employment  as  district
geologist  for Hondo  Oil & Gas  Company prior to  its sale. Mr.  Freidline is a
Certified Petroleum  Geologist,  and a  member  of the  Society  of  Exploration
Geophysicists,  the  Permian  Basin  Geophysical  Society  and  the  West  Texas
Geological Society. He has co-authored papers which have appeared in Geology and
The Bulletin of the Seismological Society  of America. Mr. Freidline received  a
B.S.  degree with  highest honors  from the New  Mexico Institute  of Mining and
Technology in  1972 and  a Masters  of  Science degree  in geophysics  from  the
University of Utah in 1974.
 
    Brian  K. Miller entered the oil and  gas business as an operations engineer
for ARCO Oil and  Gas Company. From  1984 to 1987, he  was a reservoir  engineer
with  First City  National Bank of  Midland, Texas,  and from 1987  to 1989, Mr.
Miller was an independent consulting engineer.  Prior to joining the Company  in
1992,  Mr. Miller  served as  an oil  and gas  analyst under  appointment to the
Federal Deposit Insurance Corporation. Mr. Miller is a member of the Society  of
Petroleum  Engineers. Mr. Miller  received a B.S. degree  with highest honors in
petroleum engineering  from the  University of  Texas at  Austin in  1982 and  a
Master of Business Administration degree with honors in finance in 1984.
 
    Sal  J. Pagano began  his oil and  gas career with  Amoco Production Company
where he  was  employed until  1978.  From 1978  through  1989, Mr.  Pagano  was
employed  by several independent  oil and gas  companies in Midland,  Texas in a
variety of petroleum  engineering capacities.  Prior to joining  the Company  in
1995,
 
                                       45
<PAGE>
Mr.  Pagano  was employed  by  Midland Resources  Company  from 1989  as  a vice
president. Mr. Pagano  is a registered  petroleum engineer and  a member of  the
Society of Petroleum Engineers. Mr. Pagano graduated in 1973 from the University
of Missouri at Rolla with a B.S. degree in petroleum engineering.
 
    Keith  Atwood began his  oil and gas  career with Otis  Engineering Corp. in
1974. Mr. Atwood worked as an independent  consultant from 1979 to 1983 when  he
joined  Musselman,  Owen &  King Operating  Co. to  manage field  operations. He
served in that capacity until joining  the Company in 1992. Mr. Atwood  attended
Southwest Texas State University and the University of Texas.
 
    Celia  A. Zinn joined the Company in  1996. From 1992 to 1996, she practiced
public accounting in Midland. Ms.  Zinn has 18 years  experience in the oil  and
gas  industry, including  12 years as  Controller for Clayton  W. Williams, Jr.,
Inc. from 1981  to 1992. Ms.  Zinn is  a certified public  accountant. Ms.  Zinn
graduated  from  the  University  of  Texas-Arlington in  1978  with  a  B.A. in
mathematics.
 
                                       46
<PAGE>
                    SECURITY OWNERSHIP OF CERTAIN BENEFICIAL
                             OWNERS AND MANAGEMENT
 
    The following  table sets  forth the  names  and addresses  of each  of  the
Company's  stockholders  who  beneficially own  more  than five  percent  of the
Company's Common  Stock,  the  number  of  shares  beneficially  owned  by  such
shareholders  and the percentage of the Common  Stock so owned at June 30, 1996,
assuming in each case the Corporate Reorganization had been consummated at  June
30, 1996.
 
<TABLE>
<CAPTION>
                                       AMOUNT AND NATURE OF
                                       BENEFICIAL OWNERSHIP    PERCENT OF
NAME AND ADDRESS OF BENEFICIAL OWNER           (1)                CLASS
- ------------------------------------  ----------------------  -------------
<S>                                   <C>                     <C>
Cadell S. Liedtke ..................          2,656,796              26.6%
400 W. Illinois
Midland, Texas 79701
Michael J. Grella ..................          1,558,161              15.6%
400 W. Illinois
Midland, Texas 79705
NationsBanc Capital Corp. ..........          1,080,008              10.8%
100 North Tryon Street
Charlotte, North Carolina 28255
Henry G. Musselman .................            705,035               7.0%
400 W. Illinois
Midland, Texas 79701
</TABLE>
 
- ------------------------
(1) Unless otherwise indicated, all persons own the listed shares of record.
 
    The  table  appearing  below sets  forth  information  as of  June  30, 1996
(assuming the Corporate Reorganization had  been consummated on such date)  with
respect  to  the  shares of  Common  Stock  beneficially owned  by  each  of the
Company's Directors, the Chief Executive Officer and the three other most highly
compensated executive officers for 1996 (whose annualized compensation for  such
year  based on compensation levels following  the Offering is expected to exceed
$100,000) and all Directors and executive  officers as a group, and the  percent
of the outstanding Common Stock owned by each.
 
<TABLE>
<CAPTION>
DIRECTORS AND NAMED                    AMOUNT AND NATURE OF    PERCENT OF
EXECUTIVE OFFICER                      BENEFICIAL OWNERSHIP     CLASS (1)
- ------------------------------------  ----------------------  -------------
<S>                                   <C>                     <C>
Cadell S. Liedtke...................          2,656,796              26.6%
Michael J. Grella...................          1,558,161              15.6%
Henry G. Musselman..................            705,035               7.0%
Bobby W. Page.......................             75,000(2)            0.7%
All Officers and Directors as a
group (13 persons)..................          4,994,992(2)           49.6%
</TABLE>
 
- ------------------------
(1) For the sole purpose of calculating these percentages, the shares, which the
    named  person has the  right to acquire  within 60 days,  by exercise of the
    options described in  these footnotes,  are deemed  outstanding shares  with
    respect  to  that  person's percentage  ownership  and with  respect  to the
    percentage ownership of all Officers and Directors as a group.
 
(2) Includes 75,000 shares issuable pursuant to options under the Company's 1996
    Stock Option Plan which options will be immediately exercisable upon closing
    of the Offerings at a  price equal to the  initial public offering price  of
    the Common Stock.
 
                                       47
<PAGE>
                  EXECUTIVE COMPENSATION AND OTHER INFORMATION
 
SUMMARY COMPENSATION TABLE
 
    The following table sets forth information for the Company's Chief Executive
Officer  and the  three other most  highly compensated  executive officers whose
annual compensation for the fiscal year ending December 31, 1996 is expected  to
exceed  $100,000.  Information  is  presented  for  1995,  and  for  1996  on an
annualized basis based on salaries to be effective following consummation of the
Offerings. Information for  1994 and  prior years  is not  comparable since  the
Company's  predecessor was a general partnership  in which the partners received
periodic partnership distributions in lieu of salary.
 
<TABLE>
<CAPTION>
                                                                                        LONG-TERM
                                                                                      COMPENSATION
                                                                                         AWARDS
                                                                                      -------------
                                                  ANNUAL COMPENSATION                  SECURITIES
                                   -------------------------------------------------   UNDERLYING
                                                                      OTHER ANNUAL      OPTIONS/        ALL OTHER
NAME AND PRINCIPAL POSITION          YEAR     SALARY($)  BONUS($)   COMPENSATION($)    SARS(#)(2)    COMPENSATION($)
- ---------------------------------  ---------  ---------  ---------  ----------------  -------------  ----------------
<S>                                <C>        <C>        <C>        <C>               <C>            <C>
Cadell S. Liedtke
  Chairman of the Board and Chief       1995    185,700         --             --              --               --
   Executive Officer                    1996    300,000         --             --              --               --
Michael J. Grella
  President and Chief Operating         1995    261,750         --             --              --               --
   Officer                              1996    300,000         --             --              --               --
Henry G. Musselman
                                        1995    139,800         --             --              --               --
  Executive Vice President              1996    215,000         --             --              --               --
Bobby W. Page
  Senior Vice President,
   Treasurer and Chief Financial        1995(1)        --        --            --              --               --
   Officer                              1996    150,000         --             --          75,000               --
</TABLE>
 
- ------------------------
(1) Mr. Page joined the Company in June 1996.
 
(2) The amount shown represents the number  of shares subject to a stock  option
    to  be granted upon the  closing of the Offerings  pursuant to the Company's
    1996 Stock  Option Plan  described under  "-- Benefit  Plans --  1996  Stock
    Option  Plan." The option will  be granted with an  exercise price per share
    equal to  the initial  public offering  price of  the Common  Stock will  be
    granted for a 10-year term.
 
DIRECTORS' COMPENSATION
 
    Compensation  for non-employee directors (Messrs.  Langdon and Kennedy) will
consist of an annual retainer fee of  $10,000, plus a $1,000 fee for each  Board
meeting  attended and a $1,000  fee for attending a  committee meeting held on a
day other than the same day of  a Board meeting. In addition, outside  Directors
are  participants in the Company's Outside Directors Stock Option Plan described
under "--  Benefit  Plans --  Outside  Directors Stock  Option  Plan."  Employee
Directors  do not receive compensation  for serving on the  Board or the Board's
committees.
 
EMPLOYMENT AGREEMENTS
 
    Messrs.  Liedtke,  Grella  and   Musselman  have  entered  into   employment
agreements  (the "Founders Employment  Agreements") with the  Company which will
become effective upon the closing of the Offerings and replace certain  existing
agreements.  The  Founders  Employment  Agreements  are  each  for  three years,
commencing on the closing of the Offerings and each will automatically renew for
successive one-year periods thereafter  unless the employee  is notified to  the
contrary  thereafter.  The  Founders Employment  Agreements  provide  for salary
levels for  Messrs. Liedtke,  Grella  and Musselman  of $300,000,  $300,000  and
$215,000, respectively.
 
                                       48
<PAGE>
    Each  of Messrs. Liedtke, Grella and  Musselman would receive his salary for
the remaining  term  of the  applicable  Founders Employment  Agreement  if  the
Company  were  to  terminate  such person's  employment  other  than  for cause.
However, if  such person  were  to voluntarily  leave  his employment  with  the
Company,  no  further  payments  would  be  required.  Each  Founders Employment
Agreement provides that the covered employee  will not compete with the  Company
for  a  one  year period  following  his  voluntary cessation  of  employment or
termination of  employment  for cause.  Competitive  activities are  defined  as
engaging  in the oil and gas  business in any area in  which the Company is then
active.
 
    Bobby W. Page has entered into an employment agreement (the "Page Employment
Agreement") with  the  Company effective  June  30, 1996.  The  Page  Employment
Agreement  is  for  a  period  of  three  years  from  June  30,  1996  and will
automatically renew for successive one-year  periods thereafter unless Mr.  Page
is  notified  to the  contrary  by the  Company.  The Page  Employment Agreement
provides a $25,000 bonus (which includes Mr. Page's cost of relocation), plus  a
base  salary of $150,000 until January 1,  1997; $175,000 until January 1, 1998;
and $185,000 thereafter. In addition, Mr. Page will receive options to  purchase
75,000  shares of  Common Stock, certain  insurance benefits  and other benefits
generally available  to the  Company's  employees. Mr.  Page would  receive  his
salary  for the remaining term  of the Page Employment  Agreement if the Company
were to terminate the Page Employment  Agreement other than for cause.  However,
if  Mr.  Page were  to voluntarily  leave  his employment  with the  Company, no
further payments would be required.
 
BENEFIT PLANS
 
    OUTSIDE DIRECTORS STOCK  OPTION PLAN.   The Outside  Directors Stock  Option
Plan  provides for the issuance of stock options to the outside directors of the
Company. A total  of          shares  of Common  Stock has  been authorized  and
reserved  for issuance under the plan, subject to adjustments to reflect changes
in the Company's capitalization resulting from stock splits, stock dividends and
similar events. Only outside directors are eligible to participate in the  plan.
Outside  directors  are those  directors of  the Company  who are  not executive
officers or regular salaried employees of the  Company as of the date an  option
is  granted. Under the plan, an option for        shares of Common Stock will be
granted to each person who qualifies as an outside director as of the  effective
date  of the  plan and  each year thereafter  that such  person is  elected as a
director of the  Company. The exercise  price of each  option granted under  the
plan  will be the fair market value  (as reported on the Nasdaq National Market)
of the Common Stock at the time the option is granted, and may be paid either in
cash or shares of Common Stock. Each option will be exercisable immediately, and
will expire ten years from the date  of grant. An option granted under the  plan
is not transferrable other than by will or the laws of descent and distribution.
In  the event a participant in the plan  ceases to be an outside director, other
than by reason of death  or change of control  of the Company, such  participant
may  exercise an outstanding option under the plan within ninety days after such
termination, to the extent the participant  was entitled to exercise the  option
on the date of termination. In the event of the death of a participant under the
plan,  such  participant's  option(s)  may  be  exercised  by  the  executors or
administrators of the optionee's estate or  by the legatees of such  participant
within  one year  after his death,  so long  as the term  of the  option has not
expired. The  Company does  not  receive any  consideration  upon the  grant  of
options  under the plan. The  options granted under the  plan are intended to be
non-qualifying options for  federal income tax  purposes. Because options  under
the  plan are  not generally  transferrable, do  not appear  to be  subject to a
substantial risk of forfeiture  and the exercise price  will be the fair  market
value  of the  common stock  on the  date of  grant, the  options should  not be
taxable to an optionee  until the optionee exercises  the option, at which  time
the optionee would recognize income on the difference between the exercise price
and  the fair market value of  the shares on the date  of exercise. The grant of
options under the plan should be treated as compensation paid by the Company for
purposes of  the  Company's federal  income  tax considerations.  The  Board  of
Directors  may amend the  plan without the  approval of the  stockholders of the
Company in  any respect  other  than the  following, which  require  stockholder
approval:  material increases in the number of shares which may be awarded under
the plan, material increases in the benefits accruing to participants under  the
plan,   material  modifications   of  the   requirements  for   eligibility  for
participation in the  plan, or  any other amendment  which requires  stockholder
approval  by law.  The Company  currently has  five directors,  two of  whom are
eligible to participate in the plan.
 
                                       49
<PAGE>
    1996 STOCK OPTION PLAN.   The 1996 Employee  Stock Option Plan provides  for
the  grant of qualified  stock options to  the employees of  the Company and its
subsidiaries, including officers  and directors  who are  salaried employees.  A
total  of         shares  of Common Stock  has been authorized  and reserved for
issuance under  the  plan, subject  to  adjustment  to reflect  changes  in  the
Company's  capitalization  resulting  from  stock  splits,  stock  dividends and
similar events. The plan is administered  by the Employee Plan Committee,  which
consists  of not  less than  two and not  more than  four directors  who are not
eligible to participate  in the plan.  The Committee has  the sole authority  to
interpret the plan, to determine the persons to whom options will be granted, to
determine the basis upon which the options will be granted, and to determine the
exercise  price, duration and other terms of the options to be granted under the
plan; provided that (a) the exercise price of each option granted under the plan
may not be less than the fair market  value of the Common Stock on the date  the
option  is granted (110% of fair market  value if the employee is the beneficial
owner of 10% or more of the Company's voting securities), (b) the exercise price
must be paid in cash or by surrendering previously owned shares of Common  Stock
upon  the exercise of the option, (c) the  term of the option may not exceed ten
years, and (d)  no option is  transferrable other than  by will or  the laws  of
descent  and distribution. Upon  termination of an  optionee's employment (other
than by  death  or  disability),  the  option may  be  exercised  prior  to  the
expiration  date of  the option or  within three  months after the  date of such
termination, whichever is earlier, but only  to the extent the optionee had  the
right  to exercise the option upon the date of such termination. In the event of
the death or  disability of an  optionee, the  option may be  exercised by  such
person,  his guardian, legatee  or personal representative at  any time prior to
the expiration date of the option, but  only to the extent the optionee had  the
right  to exercise the option as of the date of his death or disability. Options
may not be granted under the plan to any individual if the effect of such  grant
would permit that person to have the first opportunity to exercise such options,
in  any calendar year, for the purchase of shares having a fair market value (at
the time of grant of the option) in excess of $100,000. Neither the Company  nor
any  of  its subsidiaries  will receive  any consideration  for the  granting of
options under the plan. Options granted under the plan are intended to have  the
federal  income tax consequences of  a qualified stock option.  As a result, the
exercise of the option will not be a taxable event; the taxable event occurs  at
the  time the shares  of Common Stock  acquired upon exercise  of the option are
sold. If the optionee holds such shares for the later of two years from the date
the option was granted or one year from the date of exercise of the option,  the
difference  between the price paid for the  shares at exercise and the price for
which those shares  are sold will  be treated  as capital gains  income. If  the
optionee  does not hold the  shares for the required  holding period, the income
would be treated as ordinary income rather than capital gains income. The  grant
of  options under the  plan will be  treated as compensation  by the Company for
federal income tax purposes. The Board of Directors may amend the plan,  without
stockholder  approval,  in  any respect  other  than the  following,  which will
require stockholder approval: increasing  the total number  of shares for  which
options  may be  granted under  the plan,  changing the  minimum exercise price,
affecting outstanding options  or the unexercised  rights thereunder,  extending
the  option period,  or extending  the termination date  of the  plan. There are
currently approximately 100 persons  who are eligible  to participate under  the
plan.
 
                              CERTAIN TRANSACTIONS
 
    A&P  Meter Sales and Services, Inc.  ("A&P"), a corporation in which Messrs.
Liedtke, Grella  and  Musselman owns  60.0%  of the  outstanding  common  stock,
supplies  meter reading services which measure gas production to the Company, as
well as to unaffiliated oil and gas  companies. A&P is also engaged in the  sale
of  gas meter and regulating  equipment, and in certain  other oil field related
businesses. For the fiscal year ended  December 31, 1995, the Company  accounted
for  approximately 27% of A&P's  gross revenues. From time  to time, the Company
has advanced funds to  A&P for working capital  needs. These advances have  been
consolidated  into two promissory notes. One note was executed December 31, 1994
in the  original principal  amount of  $370,000. The  note bears  interest at  a
floating  rate equal  to the  "prime rate" plus  1.0%. No  principal or interest
payments are due until the maturity of  the note at December 31, 2004. The  note
is  secured  by  a  second  lien on  A&P's  accounts  receivable,  inventory and
equipment. The second note is in  the original principal amount of $247,000  and
is  dated May 22, 1996. The note bears  interest at 6.0% per annum, is unsecured
and is payable upon demand. During the fiscal year ended December 31, 1995,  A&P
received
 
                                       50
<PAGE>
$612,139  from the  Company for meter  reading, meter  repair, calibration, flow
line installation  and  other related  services  provided to  the  Company.  The
Company  believes that the services and charges therefor are comparable to those
the Company could have obtained from unaffiliated third parties.
 
    During 1994 and 1995, the Company paid $2,458 and $440,884, respectively, to
Valley for gas compression and salt water disposal charges. During 1995,  Valley
paid  the Company $109,399 for operating costs  of its salt water disposal wells
and gas  compressors.  Also during  1995,  the  Company paid  CSL  $592,920  for
management fees and lease payments on equipment.
 
    During  a portion of  1995, the Company  leased office space  from 511 Tex.,
L.C., in which Messrs. Liedtke, Grella  and Musselman are the sole members.  The
amount  of rental payments to 511 Tex, L.C. during 1995 was $67,896. The Company
no longer leases office space from any affiliated party.
 
    The Company  has  agreed that,  upon  the request  of  NBCC, on  up  to  two
occasions,  the  Company will  register  under the  Securities  Act of  1933, as
amended (the "Securities Act"), and applicable state securities laws the sale of
the Common Stock owned by NBCC.  The Company's obligation is subject to  certain
limitations regarding the timing of registrations and certain other matters. The
Company  is also  obligated to  offer to  NBCC and  Messrs. Liedtke,  Grella and
Musselman (collectively, the  "Affiliated Holders") the  opportunity to  include
shares  of the  Common Stock  owned by  them in  certain registration statements
filed by  the Company.  In addition,  the Company  has agreed  to indemnify  the
Affiliated   Holders  and  their  respective   officers  and  directors  against
securities law liabilities arising in connection with such offerings, other than
liabilities arising as a result of  information furnished to the Company by  the
Affiliated  Holders participating in the  registration. The Company is obligated
to  pay  all  expenses  incident  to  such  registration,  except  underwriters'
discounts  and commissions allocable to the sale of shares by Affiliated Holders
and any  professional  fees and  expenses  incurred by  the  Affiliated  Holders
incident to such registration. The Affiliated Holders have agreed that they will
not sell any shares of Common Stock for a period of 180 days after the Offerings
without the consent of Prudential Securities Incorporated.
 
    Certain   of  the  transactions   comprising  the  Corporate  Reorganization
represent transactions  between  the  Company,  or  its  predecessors,  and  its
affiliates.  Messrs. Liedtke, Grella  and Musselman, the  shareholders of Valley
and CSL will sell the stock of Valley  and the assets of CSL to the Company  for
$0.7  million.  The  purchase price  is  based on  negotiations  between Messrs.
Liedtke, Grella and Musselman, on the one hand, and NBCC, considering the  value
to  the Company of the stock and assets being acquired. No third party conducted
an appraisal of either Valley or CSL.
 
    In addition, Messrs. Liedtke, Grella and Musselman will receive an aggregate
distribution from the LLC of approximately $3.5 million which is estimated to be
the federal income tax liability (as well as the federal income tax liability on
such distribution) which will be owed  by Messrs. Liedtke, Grella and  Musselman
as a result of the Corporate Reorganization. However, the precise amount of such
liability  will be dependent upon a number of factors which cannot be determined
with certainty until  subsequent to December  31, 1996. While  the amount to  be
distributed  has  been determined  in good  faith  by the  Company's independent
accountants, there can be no assurance that  the actual tax liability of any  of
Messrs.  Liedtke,  Grella or  Musselman will  not  be less  or greater  than the
distributed  amounts.  If  the  distributed  amounts  exceed  the  ultimate  tax
liabilities,  none of such persons  will reimburse the Company. Correspondingly,
if the tax liability exceeds the amount of such distributions, the Company  will
not  make  any further  distributions  to cover  such  short-fall. NBCC  is also
receiving a  distribution  of  $800,000  which  represents  its  post-redemption
ownership  percentage of  the distribution made  to Messrs.  Liedtke, Grella and
Musselman. However, NBCC  has no  tax or other  liability with  respect to  such
distribution.
 
                      DESCRIPTION OF CERTAIN INDEBTEDNESS
 
EXISTING DEBT FACILITY
 
    In  June 1996,  the Company entered  into a credit  agreement (the "Existing
Debt Facility")  provided by  NationsBridge, L.L.C.  and NationsBank,  N.A.  and
consisting of a $95.0 million revolving credit loan (the
 
                                       51
<PAGE>
"Existing  Revolver") and a $30.0 million  term loan (the "Existing Term Loan").
The Existing Debt Facility provided funds to consummate the 1996 Acquisition and
to refinance the  Company's prior  senior bank  facility. Prudential  Securities
Group Inc. ("PGI") has purchased an interest in the Existing Debt Facility.
 
    The Existing Revolver and the Existing Term Loan each matures June 10, 1999.
No  periodic principal reductions are required with respect to the Existing Term
Loan; however, quarterly principal reductions in the amount of $3.0 million  are
required  with respect to the Existing  Revolver, commencing January 1, 1997. In
addition, the Existing  Debt Facility requires  that the net  proceeds from  the
Notes  Offering be applied to reduce  the amounts outstanding under the Existing
Revolver and the  Existing Term  Loan, and  100% of  the net  proceeds from  the
Common  Stock  Offering  are  required  to be  utilized  to  reduce  the amounts
outstanding under the Existing Term Loan and Existing Revolver.
 
    Interest accrues on  the Existing Term  Loan initially at  14.0% per  annum,
increasing  by 0.5% at per  annum the end of  each successive three month period
(commencing September 10, 1996) up to a maximum of 16.5% per annum. Interest may
be paid in cash  or "in kind"  by delivery of additional  notes having the  same
terms as the notes issued pursuant to the Existing Term Loan. Interest under the
Existing  Revolver accrues, at the option of  the Company, at a margin in excess
of either NationsBank, N.A. "LIBOR" rate, up to a maximum of 5.0% per annum,  or
NationsBank, N.A. fluctuating "prime rate" up to a maximum of 2.75% per annum.
 
    The  Existing Debt Facility is  secured by a pledge  of substantially all of
the Company's  assets, a  guaranty  by the  Company's subsidiaries  and  limited
guaranties  by  Messrs. Liedtke,  Grella  and Musselman  proportionate  to their
membership interests in the LLC.
 
CREDIT FACILITY
 
    The Company is negotiating with several banks to provide the Credit Facility
which  will  be  consummated  concurrently  with  the  Offerings.  The   Company
anticipates  that the Credit Facility will provide a revolving facility based on
the borrowing base of its oil and gas assets. Based on its negotiations to date,
the Company anticipates having approximately $50.0 million available pursuant to
the Credit  Facility,  none  of which  is  expected  to be  outstanding  at  its
inception.  The  Credit  Facility is  expected  to  be secured  by  a  pledge of
substantially all of the Company's assets. Messrs. Liedtke, Grella and Musselman
will not guaranty indebtedness due under the Credit Facility.
 
THE NOTES
 
    The Company is  concurrently offering  $100 million  in aggregate  principal
amount of the Notes by means of a separate prospectus. The closing of the Common
Stock Offering and the Notes Offering are conditioned upon each other.
 
    The  Notes will  be general  unsecured obligations  of the  Company, will be
subordinated in right of payment to all existing and future senior  indebtedness
of  the Company and will be senior in right of payment to or pari passu with all
other subordinated  indebtedness of  the Company.  The Notes  are guaranteed  by
certain  of the  Company's subsidiaries.  The Notes  will bear  interest payable
semi-annually at a rate to  be determined at the  pricing of the Notes  Offering
and will mature in 2006.
 
    The  Notes will not be redeemable  until               2001. Thereafter, the
Notes will be redeemable at any time at the option of the Company in whole or in
part at the  redemption prices  set forth  in the  Indenture. There  will be  no
mandatory  sinking  fund for  the  Notes. Upon  the  occurrence of  a  change of
control, the Company will be required to make an offer to purchase all the Notes
at 101% of the principal amount thereof, plus accrued and unpaid interest to the
date of purchase.
 
    The Indenture will contain certain covenants that, among other things, limit
the ability of the Company and certain  of its subsidiaries to pay dividends  or
make  certain other restricted payments, issue preferred stock, incur additional
indebtedness, enter into  transactions with affiliates,  incur liens, engage  in
certain  sale and  leaseback arrangements,  make certain  asset dispositions and
merge or consolidate with, or transfer
 
                                       52
<PAGE>
substantially all of its  assets to, any other  person. The Indenture will  also
contain  certain covenants  that limit the  ability of certain  of the Company's
subsidiaries to restrict  their ability  to make  payments to  the Company.  The
Indenture will contain customary events of default.
 
                          DESCRIPTION OF CAPITAL STOCK
 
    The authorized capital stock of the Company consists of 20,000,000 shares of
Common Stock, par value $0.10 per share ("Common Stock") and 3,000,000 shares of
Preferred  Stock,  par  value  $0.10 per  share  ("Preferred  Stock").  Upon the
completion of the  Offerings and  the Corporate Reorganization,  the issued  and
outstanding  capital stock of  the Company will consist  of 10,000,000 shares of
Common Stock (or 10,600,000 shares if the Underwriters' over-allotment option is
exercised in full).
 
    The following description of certain  matters relating to the capital  stock
of  the Company  is summary in  nature and is  qualified in its  entirety by the
provisions of the Company's Certificate  of Incorporation and Bylaws, copies  of
which  have been filed as  exhibits to the Registration  Statement of which this
Prospectus is a part.
 
COMMON STOCK
 
    Except as  otherwise  required by  law,  the  holders of  Common  Stock  are
entitled  to  one  vote  per  share  on  all  matters  submitted  to  a  vote of
stockholders of the Company. In addition,  such holders are entitled to  receive
ratably  such dividends,  if any, as  may be declared  from time to  time by the
Board of  Directors out  of funds  legally available  therefor, subject  to  the
payment  of preferential dividends with respect to any Preferred Stock that from
time to time may be outstanding. In the event of the dissolution, liquidation or
winding-up of the  Company, the holders  of Common Stock  are entitled to  share
ratably  in all assets remaining after payment of all liabilities of the Company
and subject to  the prior distribution  rights of the  holders of any  Preferred
Stock  that may be outstanding at that time.  The holders of Common Stock do not
have cumulative voting rights or preemptive  rights. All shares of Common  Stock
outstanding  and to be outstanding after the Common Stock Offering will be fully
paid and nonassessable.
 
PREFERRED STOCK
 
    The Board  of Directors  has  the authority  to  issue 3,000,000  shares  of
Preferred  Stock, in  one or  more series, and  to fix  the rights, preferences,
qualifications, privileges,  limitations or  restrictions  of each  such  series
without  any further vote or action  by the stockholders, including the dividend
rights, dividend rate,  conversion rights,  voting rights,  terms of  redemption
(including  sinking fund  provisions), redemption  price or  prices, liquidation
preferences and the number of shares constituting any series or the designations
of such series.  No shares of  Preferred Stock  have ever been  issued, and  the
Company  has  no  present plans  to  issue  any Preferred  Stock.  The Indenture
governing the Notes limits the issuance of Preferred Stock in some instances.
 
    While  providing   desirable  flexibility   in  connection   with   possible
acquisitions  and other  corporate purposes,  and eliminating  delays associated
with a stockholder vote on specific  issuances, the issuance of Preferred  Stock
could  adversely affect  the voting  power of  holders of  Common Stock  and the
likelihood that such holders  will receive dividend  payments and payments  upon
liquidation  and could  have the effect  of delaying, deferring  or preventing a
change in control of the Company.
 
REGISTRATION RIGHTS
 
    The Company  has  agreed that,  upon  the request  of  NBCC, on  up  to  two
occasions,  the Company  will register under  the Securities  Act and applicable
state securities laws the sale of the Common Stock owned by NBCC. The  Company's
obligation   is  subject  to   certain  limitations  regarding   the  timing  of
registrations and certain other matters. The Company is also obligated to  offer
to NBCC and Messrs. Liedtke, Grella and Musselman (collectively, the "Affiliated
Holders") the opportunity to include shares of the Common Stock owned by them in
certain  registration statements filed by the  Company. In addition, the Company
has agreed to indemnify the Affiliated Holders and their respective officers and
directors against securities  law liabilities  arising in  connection with  such
offerings,  other than liabilities arising as  a result of information furnished
by the Company by the Affiliated Holders participating in the registration.  The
Company is
 
                                       53
<PAGE>
obligated to pay all expenses incident to such registration, except underwriting
discounts  and commissions allocable to the sale of shares by Affiliated Holders
and any  professional  fees and  expenses  incurred by  the  Affiliated  Holders
incident to such registration.
 
ANTI-TAKEOVER PROVISIONS
 
    The  Certificate of Incorporation and Bylaws of the Company and the Delaware
General Corporation Law (the  "DGCL") include a number  of provisions which  may
have  the effect of encouraging persons considering unsolicited tender offers or
other unilateral takeover  proposals to  negotiate with the  Board of  Directors
rather  than pursue non-negotiated takeover attempts. These provisions include a
classified  board  of  directors,   authorized  blank  check  preferred   stock,
restrictions  on business  combinations and  the availability  of authorized but
unissued Common Stock.
 
    CLASSIFIED BOARD OF DIRECTORS.   The Company's Certificate of  Incorporation
and Bylaws contain provisions for a board of directors divided into classes with
only  one class standing for  election each year. Directors  can only be removed
for cause. A staggered board makes it more difficult for stockholders to  change
the  majority of  the directors  and instead  promotes a  continuity of existing
management.
 
    BLANK CHECK PREFERRED  STOCK.  The  Certificate of Incorporation  authorizes
blank  check Preferred Stock.  See "-- Preferred Stock."  The Board of Directors
can set the voting rights, redemption rights, conversion rights and other rights
relating to such Preferred Stock and could issue such stock in either a  private
or  public transaction. In  some circumstances, the  blank check Preferred Stock
could be issued  and have the  effect of  preventing a merger,  tender offer  or
other takeover attempt which the Board of Directors opposes.
 
DELAWARE TAKEOVER STATUTE
 
    The  Company is subject to Section 203  of the DGCL. In general, Section 203
prevents an "interested stockholder" from  engaging in a "business  combination"
with  a  Delaware corporation  for three  years following  the date  such person
became an  interested stockholder,  unless (i)  prior to  the date  such  person
became  an interested  stockholder, the  board of  directors of  the corporation
approved  the  transaction  in  which  the  interested  stockholder  became   an
interested   stockholder  or  approved  the   business  combination;  (ii)  upon
consummation of the  transaction that resulted  in the interested  stockholder's
becoming an interested stockholder, the interested stockholder owns at least 85%
of  the voting stock of the corporation  outstanding at the time the transaction
commenced, excluding  stock held  by  directors who  are  also officers  of  the
corporation  and stock  held by  certain employee  stock plans;  or (iii)  on or
subsequent to  the  date of  the  transaction in  which  such person  became  an
interested  stockholder, the  business combination is  approved by  the board of
directors of the corporation and authorized at a meeting of the stockholders  by
the  affirmative vote  of the  holders of  two-thirds of  the outstanding voting
stock of the corporation not owned by the interested stockholder.
 
    Section 203 defines a  "business combination" to include  (i) any merger  or
consolidation  involving the corporation and an interested stockholder; (ii) any
sale, transfer, pledge or other disposition involving an interested  stockholder
of  10%  or more  of the  assets of  the corporation;  (iii) subject  to certain
exceptions, any transaction  which results in  the issuance or  transfer by  the
corporation  of any stock of the  corporation to an interested stockholder; (iv)
any transaction involving the corporation which has the effect of increasing the
proportionate share  of the  stock of  any class  or series  of the  corporation
beneficially  owned  by the  interested  stockholder or  (v)  the receipt  by an
interested stockholder  of any  loans, guarantees,  pledges or  other  financial
benefits  provided by or  through the corporation. For  purposes of Section 203,
the term "corporation" also includes the Company's majority-owned  subsidiaries.
In  addition, Section  203 defines an  "interested stockholder" as  an entity or
person beneficially owning 15%  or more of the  outstanding voting stock of  the
corporation  and  any  entity  or  person  affiliated  with  or  controlling  or
controlled by such entity or person.
 
STOCKHOLDER ACTION
 
    With respect to  any act  or action  required of or  by the  holders of  the
Common  Stock, the affirmative vote of a  majority of the shares of Common Stock
present in person  or represented by  proxy at  a meeting and  entitled to  vote
thereon  is sufficient to  authorize, affirm, ratify  or consent to  such act or
actions,  except  as  otherwise  provided  by  law  or  in  the  Certificate  of
Incorporation. The DGCL requires the approval of the
 
                                       54
<PAGE>
holders  of a  majority of  the outstanding stock  entitled to  vote for certain
extraordinary corporate transactions,  such as a  merger, sale of  substantially
all assets, dissolution or amendment of the Certificate of Incorporation.
 
    Pursuant  to Delaware law, stockholders may take actions without the holding
of a  meeting  by  written consent  or  consents  signed by  the  holders  of  a
sufficient  number  of  shares  to  approve  the  transaction  had  all  of  the
outstanding shares of the capital stock of the Company entitled to vote  thereon
been  present  at  a meeting.  The  Affiliated  Holders will  own  49.2%  of the
outstanding Common Stock after the Offering. See "Security Ownership of  Certain
Beneficial  Owners and Management." Pursuant to the rules and regulations of the
Commission, if stockholder action is taken by written consent, the Company  will
be  required to send each  stockholder entitled to vote  on the matter acted on,
but  whose  consent  was  not  received,  an  information  statement  containing
information  substantially similar to that which  would have been contained in a
proxy statement.
 
TRANSFER AGENT AND REGISTRAR
 
    The  transfer   agent  and   registrar  for   the  Common   Stock  will   be
                            .
 
                                       55
<PAGE>
                        SHARES ELIGIBLE FOR FUTURE SALE
 
    Upon  completion of the Common Stock Offering, the Company will have a total
of 10,000,000 shares of Common Stock outstanding. Of these shares, the 4,000,000
shares of Common  Stock offered  hereby (4,600,000 shares  if the  Underwriters'
over-allotment  option is  exercised in  full) will  be freely  tradable without
restriction or  registration under  the  Securities Act  by persons  other  than
"affiliates"  of the Company, as defined under the Securities Act. The remaining
6,000,000 shares of Common Stock outstanding will be "restricted securities"  as
that term is defined by Rule 144 as promulgated under the Securities Act.
 
    In  general, under  Rule 144  as currently in  effect, a  person (or persons
whose shares are  aggregated) who has  beneficially owned restricted  securities
for  at least two years, including persons who may be deemed "affiliates" of the
Company, would be  entitled to sell  within any three-month  period a number  of
shares  that does not exceed the greater of  one percent of the number of shares
of Common Stock then outstanding  (approximately 100,000 shares upon  completion
of the Common Stock Offering) or the average weekly trading volume of the Common
Stock  during the four  calendar weeks preceding  the filing of  a Form 144 with
respect to such sale. Sales under Rule 144 are also subject to certain manner of
sale provisions  and notice  requirements, and  to the  availability of  current
public information about the Company. In addition, a person who is not deemed to
have been an affiliate of the Company at any time during the 90 days preceding a
sale, and who has beneficially owned the shares proposed to be sold for at least
three  years, would be  entitled to sell  such shares under  Rule 144(k) without
regard to the requirements described above.
 
    Under Rule 144 (and subject to the conditions thereof, including the  volume
limitations   described  above),   approximately  4,919,992   of  the  6,000,000
restricted shares will become eligible for  sale 90 days after the Common  Stock
Offering.  All  6,000,000  of  the  restricted  shares  are  subject  to  lockup
restrictions. Pursuant to  these restrictions  the holders  of these  restricted
shares, including certain of its executive officers and directors and NBCC, have
agreed   that  they  will  not,  subject  to  certain  exceptions,  directly  or
indirectly, offer, sell,  offer to  sell, contract  to sell,  pledge, grant  any
option  to purchase or otherwise  sell or dispose (or  announce any offer, sale,
offer of sale, contract  to sell, pledge,  grant of any  options to purchase  or
sale or disposition) of any shares of Common Stock or other capital stock of the
Company, or any securities convertible into, or exercisable or exchangeable for,
any  shares of Common  Stock or other  capital stock of  the Company without the
prior written consent of  Prudential Securities Incorporated,  on behalf of  the
Underwriters,  for a period of 180 days  from the date of this Prospectus. After
such 180-day period,  this restriction will  expire and shares  permitted to  be
sold  under Rule 144  would be eligible  for sale. In  addition, NBCC has demand
registration rights  to require  the  Company to  file  up to  two  registration
statements  under the Securities Act of the  shares of Common Stock held by such
holder and the  other major stockholders  have "piggyback" registration  rights,
which  would permit  such holders to  resell such shares  without complying with
Rule 144. Registration and sale of such  shares could have an adverse effect  on
the  trading price of the Common Stock. The Company currently has only one stock
option outstanding  for 75,000  shares. See  "Executive Compensation  and  Other
Information."
 
    Prior  to the Common Stock Offering, there has been no public market for the
Common Stock and no predictions can be made of the effect, if any, that the sale
or availability for sale of shares of  additional Common Stock will have on  the
market  price of the Common Stock. Nevertheless, sales of substantial amounts of
such shares in the public market, or the perception that such sales could occur,
could materially and adversely affect the  market price of the Common Stock  and
could  impair the Company's future ability  to raise capital through an offering
of its equity securities.
 
                                       56
<PAGE>
                                  UNDERWRITING
 
    The Underwriters  named  below  (the "Underwriters"),  for  whom  Prudential
Securities  Incorporated  and  Rauscher  Pierce  Refsnes,  Inc.  are  acting  as
Representatives, have  severally agreed,  subject to  the terms  and  conditions
contained in the Underwriting Agreement, to purchase from the Company the number
of shares of Common Stock set forth below opposite their respective names:
 
<TABLE>
<CAPTION>
                                                                                           NUMBER
            UNDERWRITER                                                                  OF SHARES
- ---------------------------------------------------------------------------------------  ----------
<S>                                                                                      <C>
Prudential Securities Incorporated.....................................................
Rauscher Pierce Refsnes, Inc...........................................................
 
                                                                                         ----------
  Total................................................................................   4,000,000
                                                                                         ----------
                                                                                         ----------
</TABLE>
 
    The  Company is  obligated to  sell, and  the Underwriters  are obligated to
purchase, all of the shares of Common Stock offered hereby if any are purchased.
 
    The Underwriters, through the Representatives, have advised the Company that
they propose  to  offer the  shares  of Common  Stock  initially at  the  public
offering  price  set  forth on  the  cover  page of  this  Prospectus;  that the
Underwriters may allow to selected dealers a concession of $      per share; and
that such dealers may reallow a concession of $      per share to certain  other
dealers.  After  the  initial  public  offering,  the  offering  price  and  the
concessions may be changed by the Representatives.
 
    The Company has granted  to the Underwriters an  option, exercisable for  30
days  from the  date of  this Prospectus, to  purchase up  to 600,000 additional
shares of Common Stock  at the initial public  offering price less  underwriting
discounts  and commissions, as set  forth on the cover  page of this Prospectus.
The Underwriters may  exercise such option  solely for the  purpose of  covering
over-allotments  incurred  in the  sale of  the shares  of Common  Stock offered
hereby. To the  extent such option  to purchase is  exercised, each  Underwriter
will  become obligated, subject to certain conditions, to purchase approximately
the same percentage of such additional shares as the number of shares set  forth
opposite each Underwriters' name in the preceding table bears to 4,000,000.
 
    The  Company, its executive officers and directors, and all of the Company's
stockholders have  agreed that  they will  not, directly  or indirectly,  offer,
sell,  offer to sell, contract to sell, pledge, grant any option to purchase, or
otherwise sell  or dispose  of (or  announce  any offer,  sale, offer  of  sale,
contract  of sale,  pledge, grant  of any  option to  purchase or  other sale or
disposition) of any  shares of  Common Stock of  the Company  or any  securities
convertible into, or exercisable or exchangeable for, any shares of Common Stock
or  other capital  stock of  the Company  without the  prior written  consent of
Prudential Securities Incorporated, on behalf of the Underwriters, for a  period
of 180 days after the date of this Prospectus.
 
    The  Company  has  agreed  to  indemnify  the  several  Underwriters  or  to
contribute to losses arising out  of certain liabilities, including  liabilities
under the Securities Act.
 
    The  Representatives have informed the Company  that the Underwriters do not
intend to confirm sales to any  accounts over which they exercise  discretionary
authority.
 
    Prior  to the Common Stock Offering, there has been no public market for the
Common Stock of the Company. Consequently, the initial public offering price for
the Common Stock will be determined through negotiation between the Company  and
the  Representatives of the Underwriters. Among  the factors to be considered in
making such determination will be the prevailing market conditions, the  results
of operations of the Company in recent periods relevant to its prospects and the
prospects  for its industry  in general, the  management of the  Company and the
market prices of securities for companies  in businesses similar to that of  the
Company.
 
                                       57
<PAGE>
    PGI  is  a lender  under  the Existing  Debt  Facility. See  "Description of
Certain Indebtedness." The lenders under the Existing Debt Facility will receive
customary fees and other compensation. PGI will receive its proportionate  share
of  the repayment by the Company of  borrowings under the Existing Debt Facility
from the net proceeds of the Notes Offering. Prudential Securities  Incorporated
is  also acting as an underwriter in the Company's concurrent Notes Offering for
which it will receive customary underwriting discounts and commissions.
 
                                 LEGAL MATTERS
 
    Certain legal matters related to the  Common Stock offered hereby are  being
passed  upon for the Company by Cotton,  Bledsoe, Tighe & Dawson, a Professional
Corporation, Midland,  Texas.  Certain  matters  will be  passed  upon  for  the
Underwriters by Baker & Botts, L.L.P., Houston, Texas.
 
                                    EXPERTS
 
    The  consolidated  financial  statements  of  Costilla  Energy,  L.L.C.  and
subsidiaries as of December 31, 1995 and for the year then ended, the statements
of revenues and direct operating expenses of the 1996 Acquisition for the  years
ended  December 31,  1993, 1994  and 1995,  and the  statements of  revenues and
direct operating expenses of the 1995  Acquisition for the years ended  December
31, 1993 and 1994, and the period ended June 12, 1995, have been included herein
and  in the  registration statement  in reliance  upon the  report of  KPMG Peat
Marwick LLP,  independent  certified  public  accountants,  appearing  elsewhere
herein,  and  upon the  authority  of said  firm  as experts  in  accounting and
auditing.
 
    The  consolidated  financial  statements  of  Costilla  Energy,  L.L.C.  and
subsidiaries  as of December 31, 1994, and for the years ended December 31, 1993
and 1994,  have  been included  herein  and  in the  registration  statement  in
reliance  upon  the report  of Elms,  Faris &  Co., P.C.,  independent certified
public accountants, appearing elsewhere herein,  and upon the authority of  said
firm as experts in accounting and auditing.
 
    In  September 1995, the Company changed its principal accountants from Elms,
Faris & Co., P.C. to  KPMG Peat Marwick LLP. The  reports of Elms, Faris &  Co.,
P.C.  on the Company's financial statements for the year ended December 31, 1994
did not  contain an  adverse opinion  or a  disclaimer of  opinion, nor  was  it
qualified  or modified in any  way as to uncertainty,  audit scope or accounting
principles. Moreover, there were no disagreements  with Elms, Faris & Co.,  P.C.
on  any  matter  of  accounting  principles  or  practices,  financial statement
disclosure, or auditing scope or procedure.
 
    Certain  information  appearing  in  this  Prospectus  regarding   estimated
quantities  of oil and gas  reserves and the discounted  present value of future
pre-tax cash flows therefrom attributable to the Company's properties and to the
properties included in  the 1996  Acquisition is  based upon  estimates of  such
reserves  and present values prepared  by Williamson Petroleum Consultants, Inc.
All of  such  information has  been  so included  herein  in reliance  upon  the
authority  of such firm as  experts in such matters. Set  forth as Appendix A is
Williamson's Summary Reserve Report dated July 23, 1996 with respect to the  oil
and  gas interests of the Company and with respect to properties acquired in the
1996 Acquisition.
 
                             AVAILABLE INFORMATION
 
    Upon completion  of  the Offerings,  the  Company  will be  subject  to  the
informational  requirements of the  Securities Exchange Act  of 1934, as amended
(the "Exchange Act"),  and, in  accordance therewith, will  file reports,  proxy
statements  and other  information with  the Securities  and Exchange Commission
(the "Commission"). Such reports, proxy  statements and other information  filed
by  the Company  with the  Commission can be  inspected at  the Public Reference
Section of the Commission at Room 1024, Judiciary Plaza, 450 Fifth Street, N.W.,
Washington, D.C. 20549, and the Regional  Offices of the Commission at  Citicorp
Center, 500 West Madison Street, Suite 1400, Chicago, Illinois 60661-2511, and 7
World  Trade Center, New York, New York  10048. Copies of such material can also
be obtained from the  Public Reference Section of  the Commission at Room  1024,
Judiciary   Plaza,   450   Fifth   Street,   N.W.,   Washington,   D.C.   20549,
 
                                       58
<PAGE>
at prescribed  rates. The  Commission maintains  a World  Wide Web  site on  the
Internet  at  HTTP:\\WWW.SEC.GOV that  contains  reports, proxy  and information
statements and other information regarding registrants that file  electronically
with the Commission.
 
    The  Company has filed with the  Commission a Registration Statement on Form
S-1 under the Securities  Act with respect to  the Common Stock offered  hereby.
This  Prospectus, which constitutes  a part of  the Registration Statement, does
not contain all  of the  information set  forth in  the Registration  Statement,
certain  items of which are contained  in exhibits to the Registration Statement
as permitted  by  the rules  and  regulations  of the  Commission.  For  further
information  with respect  to the Company  and the Common  Stock offered hereby,
reference is made to the Registration Statement, including the exhibits thereto,
which may  be  inspected  without  charge at  the  public  reference  facilities
maintained  by the Commission at 450  Fifth Street, N.W., Washington, D.C. 20549
and at  the Regional  Offices of  the Commission,  and copies  of which  may  be
obtained  from  the  Commission at  prescribed  rates. Statements  made  in this
Prospectus concerning the contents  of any document referred  to herein are  not
necessarily  complete.  With  respect  to  each  such  document  filed  with the
Commission as an exhibit to the Registration Statement, reference is made to the
exhibit for a more  complete description of the  matter involved, and each  such
statement made herein shall be deemed qualified by such reference.
 
                                       59
<PAGE>
                                    GLOSSARY
 
    The terms defined in this section are used throughout this Prospectus.
 
    ALL-IN  FINDING COSTS.  The amount  of total capital expenditures, including
acquisition costs,  and  exploration  and  abandonment costs  for  oil  and  gas
activities  divided by  the amount of  proved reserves (expressed  in BOE) added
during the specified period (including the effect on proved reserves of  reserve
revisions).
 
    BBL.   One stock tank barrel, or  42 U.S. gallons liquid volume, used herein
in reference to crude oil or other liquid hydrocarbons.
 
    BCF.  One billion cubic feet.
 
    BOE.  Equivalent barrels  of oil. In reference  to natural gas, natural  gas
equivalents  are determined using the ratio of six Mcf of natural gas to one Bbl
of crude oil, condensate or natural gas liquids.
 
    BTU.  One British thermal unit. The  quantity of heat required to raise  the
temperature of one pound of water one degree Fahrenheit.
 
    DEVELOPED ACREAGE.  The number of acres which are allocated or assignable to
producing wells or wells capable of production.
 
    DEVELOPMENT  WELL.  A well  drilled within the proved area  of an oil or gas
reservoir to the depth of a stratigraphic horizon known to be productive.
 
    DRY WELL.  A well  found to be incapable of  producing either oil or gas  in
sufficient quantifies to justify completion of an oil or gas well.
 
    EBITDA.     Calculated  by  adding  interest,  income  taxes,  depreciation,
depletion and amortization and exploration  and abandonment costs to net  income
(loss).
 
    EXPLORATORY  WELL.   A well  drilled to find  and produce  oil or  gas in an
unproved area,  to find  a  new reservoir  in a  field  previously found  to  be
productive of oil or gas in another reservoir, or to extend a known reservoir.
 
    GROSS  ACRES OR GROSS WELLS.  The total  acres or wells, as the case may be,
in which a working interest is owned.
 
    MBBL.  One thousand barrels of crude oil or other liquid hydrocarbons.
 
    MBOE.  One thousand barrels of oil equivalent.
 
    MMBOE.  One million barrels of oil equivalent.
 
    MMBBLS.  One million barrels of crude oil or other liquid hydrocarbons.
 
    MMBTU.  One million Btu's.
 
    MCF.  One thousand cubic feet.
 
    MMCF.  One million cubic feet.
 
    NET ACRES OR NET WELLS.  The  sum of the fractional working interests  owned
in gross acres or gross wells.
 
    PRESENT  VALUE OF ESTIMATED FUTURE NET REVENUES OR PV-10 VALUE.  The present
value of estimated  future net revenues  is an estimate  of future net  revenues
from  a property at its  acquisition date, at a  specified date, after deducting
production and ad valorem  taxes, future capital  costs and operating  expenses,
but  before deducting  federal income taxes.  The future net  revenues have been
discounted at an  annual rate  of 10% to  determine their  "present value."  The
present  value is  shown to  indicate the  effect of  time on  the value  of the
revenue stream and should not  construed as being the  fair market value of  the
properties.  Estimates have been made using  constant oil and natural gas prices
and operating costs at the specified date.
 
    PRODUCTIVE WELL.  A  well that is  producing oil or gas  that is capable  of
production.
 
                                       60
<PAGE>
    PROVED  DEVELOPED RESERVES.   Reserves that can be  expected to be recovered
through existing wells with existing equipment and operating methods.
 
    PROVED RESERVES.   The estimated quantities  of crude oil,  natural gas  and
natural  gas  liquids which  geological  and engineering  data  demonstrate with
reasonable certainty to  be recoverable  in future years  from known  reservoirs
under existing economic and operating conditions.
 
    PROVED  UNDEVELOPED RESERVES.   Reserves that  are expected  to be recovered
from new wells on undrilled acreage,  or from existing wells where a  relatively
major expenditure is required for recompletion.
 
    ROYALTY  INTEREST.   An interest  in an oil  and gas  property entitling the
owner to a share of oil and gas production free of costs of production.
 
    3-D SEISMIC.    Advanced technology  method  of detecting  accumulations  of
hydrocarbons  identified by the collection and  measurement of the intensity and
timing of sound waves  transmitted into the  earth as they  reflect back to  the
surface.
 
    UNDEVELOPED  ACREAGE.  Lease acreage on which wells have not been drilled or
completed to a point that would  permit the production of commercial  quantities
of oil and gas regardless of whether such acreage contains proved reserves.
 
    WORKING INTEREST.  The operating interest which gives the owner the right to
drill,  produce and conduct operating activities on  the property and a share of
production.
 
                                       61
<PAGE>
                         INDEX TO FINANCIAL STATEMENTS
 
<TABLE>
<S>                                                                                    <C>
Financial Statements of Costilla Energy, L.L.C.:
  Independent Auditors' Reports......................................................        F-2
  Consolidated Balance Sheets as of December 31, 1994 and 1995, and March 31, 1996
   (unaudited).......................................................................        F-4
  Consolidated Statements of Operations for the Years Ended December 31, 1993, 1994,
   and 1995, and the Three Months ended March 31, 1995 and 1996 (unaudited)..........        F-5
  Consolidated Statements of Members' Capital for the Years Ended December 31, 1993,
   1994, and 1995, and the Three Months ended March 31, 1996 (unaudited).............        F-6
  Consolidated Statements of Cash Flows for the Years Ended December 31, 1993, 1994,
   and 1995, and the Three Months ended March 31, 1995 and 1996 (unaudited)..........        F-7
  Notes to Consolidated Financial Statements.........................................        F-8
 
Financial Statements of the 1995 Acquisition:
  Independent Auditors' Report.......................................................       F-21
  Statements of Revenues and Direct Operating Expenses for the Years Ended December
   31, 1993 and 1994 and the period ended June 12, 1995..............................       F-22
  Notes to the Statements of Revenues and Direct Operating Expenses..................       F-23
 
Financial Statements of the 1996 Acquisition:
  Independent Auditors' Report.......................................................       F-26
  Statements of Revenues and Direct Operating Expenses for the Years Ended December
   31, 1993, 1994 and 1995, and the periods ended March 31, 1995 and 1996
   (unaudited).......................................................................       F-27
  Notes to the Statements of Revenues and Direct Operating Expenses..................       F-28
</TABLE>
 
                                      F-1
<PAGE>
                          INDEPENDENT AUDITORS' REPORT
 
The Members
Costilla Energy, L.L.C. (a Texas limited liability company):
 
    We  have  audited the  accompanying consolidated  balance sheet  of Costilla
Energy, L.L.C.  (a  Texas limited  liability  company) and  subsidiaries  as  of
December  31,  1995,  and  the  related  consolidated  statement  of operations,
members' capital, and  cash flows for  the year then  ended. These  consolidated
financial  statements are  the responsibility  of the  Company's management. Our
responsibility is to express an opinion  on these financial statements based  on
our audit.
 
    We  conducted  our  audit  in accordance  with  generally  accepted auditing
standards. Those standards require that we plan and perform the audit to  obtain
reasonable assurance about whether the financial statements are free of material
misstatement.  An audit includes examining, on a test basis, evidence supporting
the amounts and disclosures in the financial statements. An audit also  includes
assessing  the  accounting principles  used  and significant  estimates  made by
management, as well as evaluating the overall financial statement  presentation.
We believe that our audit provides a reasonable basis for our opinion.
 
    In  our  opinion, the  consolidated financial  statements referred  to above
present fairly, in  all material  respects, the financial  position of  Costilla
Energy,  L.L.C. and  subsidiaries as  of December 31,  1995, and  the results of
their operations and  their cash flows  for the year  then ended, in  conformity
with generally accepted accounting principles.
 
                                                           KPMG PEAT MARWICK LLP
 
Midland, Texas
April 16, 1996 (except  with respect to matters  discussed in the last paragraph
               of Note 7 and Note 12, as to which the date is May 28, 1996.)
 
                                      F-2
<PAGE>
                          INDEPENDENT AUDITORS' REPORT
 
The Members
Costilla Energy, L.L.C.:
 
    We have  audited the  accompanying consolidated  balance sheet  of  Costilla
Energy,  L.L.C.  (a  Texas  limited  liability  company)  and  subsidiaries (the
combination of  CSL  Partners,  Costilla  Petroleum  Corporation  and  Statewide
Minerals, L.C.) as of December 31, 1994, and the related consolidated statements
of operations, members' capital, and cash flows for the years ended December 31,
1993 and 1994. These consolidated financial statements are the responsibility of
the  Company's management. Our responsibility is  to express an opinion on these
financial statements based on our audits.
 
    We conducted  our  audits in  accordance  with generally  accepted  auditing
standards. Those standards require that we plan and perform the audits to obtain
reasonable assurance about whether the financial statements are free of material
misstatement.  An audit includes examining, on a test basis, evidence supporting
the amounts and disclosures in the financial statements. An audit also  includes
assessing  the  accounting principles  used  and significant  estimates  made by
management, as well as evaluating the overall financial statement  presentation.
We believe that our audits provides a reasonable basis for our opinion.
 
    In  our  opinion, the  consolidated financial  statements referred  to above
present fairly, in all material respects, the consolidated financial position of
Costilla Energy,  L.L.C. and  subsidiaries  as of  December  31, 1994,  and  the
results  of their operations and  their cash flows for  the years ended December
31, 1993 and 1994, in conformity with generally accepted accounting principles.
 
                                          ELMS, FARIS & CO., P.C.
 
Midland, Texas
March 31, 1995
 
                                      F-3
<PAGE>
                            COSTILLA ENERGY, L.L.C.
                      (A TEXAS LIMITED LIABILITY COMPANY)
                          CONSOLIDATED BALANCE SHEETS
                                 (IN THOUSANDS)
 
                                     ASSETS
<TABLE>
<CAPTION>
                                                                                              DECEMBER 31,
                                                                                            ----------------   MARCH 31,
                                                                                             1994     1995       1996
                                                                                            -------  -------  -----------
                                                                                                              (UNAUDITED)
<S>                                                                                         <C>      <C>      <C>
Current assets:
  Cash and cash equivalents...............................................................  $   137  $ 2,616    $ 2,760
  Restricted cash.........................................................................       --      250        250
  Accounts receivable:
    Trade, net............................................................................    1,042    3,154      2,401
    Affiliates............................................................................       --      507        994
    Oil and gas sales.....................................................................    1,715    3,915      4,189
  Prepaid and other current assets........................................................      223      439        800
                                                                                            -------  -------  -----------
        Total current assets..............................................................    3,117   10,881     11,394
                                                                                            -------  -------  -----------
Property, plant and equipment, at cost:
  Oil and gas properties, using the successful efforts method of accounting:
    Proved properties.....................................................................   22,794   79,897     83,965
    Unproved properties...................................................................    2,060    2,903      3,580
  Accumulated depletion, depreciation and amortization....................................   (3,562)  (9,413)   (11,281)
                                                                                            -------  -------  -----------
                                                                                             21,292   73,387     76,264
                                                                                            -------  -------  -----------
Other property and equipment, net.........................................................       76      679      1,024
Deferred charges (Note 2).................................................................       29    1,736      1,658
Note receivable -- affiliate..............................................................      390      684        684
                                                                                            -------  -------  -----------
                                                                                            $24,904  $87,367    $91,024
                                                                                            -------  -------  -----------
                                                                                            -------  -------  -----------
 
<CAPTION>
 
                              LIABILITIES, REDEEMABLE MEMBERS' CAPITAL AND MEMBERS' CAPITAL
<S>                                                                                         <C>      <C>      <C>
Current liabilities:
  Current maturities of long-term debt....................................................  $    22  $    --    $    --
  Trade accounts payable..................................................................    1,712    5,467      6,190
  Undistributed revenue...................................................................      110    1,227      1,026
  Other current liabilities...............................................................      192    1,691      2,074
                                                                                            -------  -------  -----------
        Total current liabilities.........................................................    2,036    8,385      9,290
                                                                                            -------  -------  -----------
Long-term debt, less current maturities (Note 7)..........................................   23,591   71,494     74,494
Deferred income (Note 2)..................................................................       24    3,319      3,097
Other noncurrent liabilities..............................................................       --       38         --
                                                                                            -------  -------  -----------
        Total liabilities.................................................................   25,651   83,236     86,881
                                                                                            -------  -------  -----------
Redeemable members' capital (Note 10).....................................................       --   11,320     11,678
                                                                                            -------  -------  -----------
Members' capital (Note 10)................................................................     (747)  (7,189)    (7,535)
Commitments and contingencies (Note 8)....................................................       --       --         --
                                                                                            -------  -------  -----------
                                                                                            $24,904  $87,367    $91,024
                                                                                            -------  -------  -----------
                                                                                            -------  -------  -----------
</TABLE>
 
          See accompanying notes to consolidated financial statements.
 
                                      F-4
<PAGE>
                            COSTILLA ENERGY, L.L.C.
                      (A TEXAS LIMITED LIABILITY COMPANY)
                     CONSOLIDATED STATEMENTS OF OPERATIONS
                                 (IN THOUSANDS)
 
<TABLE>
<CAPTION>
                                                                                                   THREE MONTHS ENDED
                                                                    YEARS ENDED DECEMBER 31,           MARCH 31,
                                                                 -------------------------------  --------------------
                                                                   1993       1994       1995       1995       1996
                                                                 ---------  ---------  ---------  ---------  ---------
                                                                                                      (UNAUDITED)
<S>                                                              <C>        <C>        <C>        <C>        <C>
Revenues:
  Oil and gas sales............................................  $   4,231  $   7,637  $  21,693  $   2,177  $   8,833
  Interest and other...........................................         56         87        123          3         88
  Gain on sale of assets.......................................        110        112         --         --         30
                                                                 ---------  ---------  ---------  ---------  ---------
                                                                     4,397      7,836     21,816      2,180      8,951
                                                                 ---------  ---------  ---------  ---------  ---------
Expenses:
  Oil and gas production.......................................      1,688      2,351     10,355        896      3,659
  General and administrative...................................        952      1,184      3,571        459      1,362
  Exploration and abandonments.................................        218        793      1,650      1,007        228
  Depreciation, depletion and amortization.....................        884      1,847      6,095        462      1,986
  Interest.....................................................        605      1,458      4,454        407      1,704
  Other........................................................         --         --          2         --         --
                                                                 ---------  ---------  ---------  ---------  ---------
                                                                     4,347      7,633     26,127      3,231      8,939
                                                                 ---------  ---------  ---------  ---------  ---------
    Net income (loss) before federal income taxes..............  $      50  $     203  $  (4,311) $  (1,051)        12
Provision for federal income taxes
  Current......................................................        (25)         8          3         --         --
  Deferred.....................................................          2         32         --         --         --
                                                                 ---------  ---------  ---------  ---------  ---------
    Net income (loss)..........................................  $      73  $     163  $  (4,314) $  (1,051) $      12
                                                                 ---------  ---------  ---------  ---------  ---------
                                                                 ---------  ---------  ---------  ---------  ---------
</TABLE>
 
          See accompanying notes to consolidated financial statements.
 
                                      F-5
<PAGE>
                            COSTILLA ENERGY, L.L.C.
                      (A TEXAS LIMITED LIABILITY COMPANY)
                  CONSOLIDATED STATEMENTS OF MEMBERS' CAPITAL
                                 (IN THOUSANDS)
 
<TABLE>
<CAPTION>
                                                                                                          MEMBERS'
                                                                                                           CAPITAL
                                                                                                         -----------
<S>                                                                                                      <C>
Balance at January 1, 1993.............................................................................   $     433
  Net income...........................................................................................          73
  Contributions........................................................................................           1
  Withdrawals..........................................................................................        (456)
                                                                                                         -----------
Balance at December 31, 1993...........................................................................          51
  Net income...........................................................................................         163
  Withdrawals..........................................................................................        (961)
                                                                                                         -----------
Balance at December 31, 1994...........................................................................        (747)
  Issuance costs (Note 10).............................................................................        (753)
  Net loss.............................................................................................      (4,314)
  Withdrawals..........................................................................................         (55)
  Preferred return on redeemable members' capital......................................................      (1,320)
                                                                                                         -----------
Balance at December 31, 1995...........................................................................      (7,189)
  Net income (unaudited)...............................................................................          12
  Preferred return on redeemable members' capital (unaudited)..........................................        (358)
                                                                                                         -----------
Balance at March 31, 1996 (unaudited)..................................................................   $  (7,535)
                                                                                                         -----------
                                                                                                         -----------
</TABLE>
 
          See accompanying notes to consolidated financial statements.
 
                                      F-6
<PAGE>
                            COSTILLA ENERGY, L.L.C.
                      (A TEXAS LIMITED LIABILITY COMPANY)
                     CONSOLIDATED STATEMENTS OF CASH FLOWS
                                 (IN THOUSANDS)
<TABLE>
<CAPTION>
                                                                                                                   THREE
                                                                                                                  MONTHS
                                                                                                                   ENDED
                                                                                  YEARS ENDED DECEMBER 31,       MARCH 31,
                                                                              ---------------------------------  ---------
                                                                                1993        1994        1995
                                                                              ---------  ----------  ----------    1995
                                                                                                                 ---------
                                                                                                                 (UNAUDITED)
<S>                                                                           <C>        <C>         <C>         <C>
Cash flows from operating activities:
  Net income (loss).........................................................  $      73  $      163  $   (4,314) $  (1,051)
  Adjustments to reconcile net income (loss) to net cash provided by
   operating activities:
    Depreciation and amortization...........................................        884       1,847       5,958        462
    Amortization of deferred charges........................................         --          --         137         --
    Other noncash...........................................................        (21)         35         (75)       (67)
    Gain on sale of oil and gas properties..................................       (110)       (112)         --         --
    Change in operating assets and liabilities:
      Increase in accounts receivable.......................................       (837)     (1,535)     (4,818)    (1,562)
      Decrease (increase) in other assets...................................         20         301        (216)      (146)
      Increase in accounts payable..........................................        262         723       4,863        537
      Increase in other liabilities.........................................         59         102       1,537         --
      Increase (decrease) in deferred income................................         (8)          3       3,294         --
                                                                              ---------  ----------  ----------  ---------
        Total adjustments...................................................        249       1,364      10,680       (776)
                                                                              ---------  ----------  ----------  ---------
        Net cash provided by (used in) operating activities.................        322       1,527       6,366     (1,827)
                                                                              ---------  ----------  ----------  ---------
Cash flows from investing activities:
  Capital expenditures for oil and gas properties...........................     (6,634)    (11,819)    (61,500)    (1,342)
  Proceeds from sale of oil and gas properties..............................        131         112          --         --
  Additions to other property and equipment.................................       (228)        (49)       (720)       (47)
  Advances on affiliate notes receivable....................................         --        (390)       (247)        --
                                                                              ---------  ----------  ----------  ---------
        Net cash used in investing activities...............................     (6,731)    (12,146)    (62,467)    (1,389)
                                                                              ---------  ----------  ----------  ---------
Cash flows from financing activities:
  Borrowings under long-term debt...........................................      6,770      11,579      62,704      1,960
  Payments of long-term debt................................................         --          --     (11,232)    (7,880)
  Deferred loan and financing costs.........................................         --          --      (2,587)      (753)
  Proceeds from redeemable members' capital.................................         --          --      10,000     10,000
  Contributions.............................................................          1          --          --         --
  Withdrawals...............................................................       (456)       (961)        (55)       (55)
                                                                              ---------  ----------  ----------  ---------
        Net cash provided by financing activities...........................      6,315      10,618      58,830      3,272
                                                                              ---------  ----------  ----------  ---------
Net increase (decrease) in cash and cash equivalents........................        (94)         (1)      2,729         56
Cash and cash equivalents, beginning of period..............................        232         138         137        137
                                                                              ---------  ----------  ----------  ---------
Cash and cash equivalents, end of period....................................  $     138  $      137  $    2,866  $     193
                                                                              ---------  ----------  ----------  ---------
                                                                              ---------  ----------  ----------  ---------
 
<CAPTION>
 
                                                                                1996
                                                                              ---------
 
<S>                                                                           <C>
Cash flows from operating activities:
  Net income (loss).........................................................  $      12
  Adjustments to reconcile net income (loss) to net cash provided by
   operating activities:
    Depreciation and amortization...........................................      1,986
    Amortization of deferred charges........................................         78
    Other noncash...........................................................        (47)
    Gain on sale of oil and gas properties..................................        (30)
    Change in operating assets and liabilities:
      Increase in accounts receivable.......................................         (7)
      Decrease (increase) in other assets...................................       (361)
      Increase in accounts payable..........................................        522
      Increase in other liabilities.........................................        345
      Increase (decrease) in deferred income................................       (222)
                                                                              ---------
        Total adjustments...................................................      2,264
                                                                              ---------
        Net cash provided by (used in) operating activities.................      2,276
                                                                              ---------
Cash flows from investing activities:
  Capital expenditures for oil and gas properties...........................     (4,749)
  Proceeds from sale of oil and gas properties..............................         --
  Additions to other property and equipment.................................       (383)
  Advances on affiliate notes receivable....................................         --
                                                                              ---------
        Net cash used in investing activities...............................     (5,132)
                                                                              ---------
Cash flows from financing activities:
  Borrowings under long-term debt...........................................      3,000
  Payments of long-term debt................................................         --
  Deferred loan and financing costs.........................................         --
  Proceeds from redeemable members' capital.................................         --
  Contributions.............................................................         --
  Withdrawals...............................................................         --
                                                                              ---------
        Net cash provided by financing activities...........................      3,000
                                                                              ---------
Net increase (decrease) in cash and cash equivalents........................        144
Cash and cash equivalents, beginning of period..............................      2,866
                                                                              ---------
Cash and cash equivalents, end of period....................................  $   3,010
                                                                              ---------
                                                                              ---------
</TABLE>
 
          See accompanying notes to consolidated financial statements.
 
                                      F-7
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS
 
        (THE INFORMATION AND AMOUNTS FOR INTERIM PERIODS ARE UNAUDITED.)
 
(1) ORGANIZATION AND NATURE OF OPERATIONS
    Costilla  Energy, L.L.C. (the "Company"), a Texas limited liability company,
was formed on  February 14,  1995, as  the successor  to CSL  Partners, a  Texas
general  partnership, which was organized on January 11, 1989. The Company is an
unincorporated association of  several individuals  and a  corporation and  will
cease  to exist thirty (30)  years from the date  of formation. Its members have
limited personal liability for the Company's obligations and debts. The  Company
is classified as a partnership for federal income tax purposes.
 
    The  Company  is an  oil  and gas  exploration  and production  concern with
properties located  principally  in  West  Texas, South  Texas,  and  the  Rocky
Mountain regions of the United States.
 
(2) SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
 
    PRINCIPLES OF CONSOLIDATION
 
    As  of December 31, 1995, the  consolidated financial statements include the
accounts of  the  Company and  its  wholly-owned subsidiaries.  All  significant
accounts  and transactions  between the Company  and its  subsidiaries have been
eliminated. At  December 31,  1993 and  1994, the  financial statements  of  the
Company  and its affiliates were combined. Significant intercompany transactions
were eliminated.
 
    USE OF ESTIMATES
 
    Preparation  of  the  accompanying  consolidated  financial  statements   in
conformity  with generally accepted accounting principles requires management to
make estimates and assumptions  that affect the reported  amounts of assets  and
liabilities  and disclosure of contingent assets  and liabilities at the date of
the financial  statements and  the  reported amounts  of revenues  and  expenses
during the reporting period. Actual results could differ from those estimates.
 
    CASH AND CASH EQUIVALENTS
 
    For  purposes of  the statements  of cash  flows, cash  and cash equivalents
include cash on hand and depository accounts held by banks.
 
    CONCENTRATIONS OF CREDIT RISK
 
    Financial instruments that potentially expose the Company to  concentrations
of   credit  risk  consist  primarily  of  unsecured  accounts  receivable  from
unaffiliated working interest owners and crude oil and natural gas purchasers.
 
    HEDGING
 
    Premiums  paid  for  commodity  option  contracts  and  interest  rate  swap
agreements   are  amortized  to   oil  and  gas   sales  and  interest  expense,
respectively, over  the  terms  of  the  agreements.  Unamortized  premiums  are
included  in other assets in the  consolidated balance sheet. Amounts receivable
under the  commodity option  contracts  and interest  rate swap  agreements  are
accrued as an increase in oil and gas sales and a reduction of interest expense,
respectively, for the applicable periods.
 
    OIL AND GAS PROPERTIES
 
    The Company uses the successful efforts method of accounting for oil and gas
producing  activities.  Costs  to  acquire  mineral  interests  in  oil  and gas
properties, to drill and equip exploratory wells that find proved reserves,  and
to drill and equip development wells are capitalized. Costs to drill exploratory
wells  that do not  find proved reserves, geological  and geophysical costs, and
costs of carrying and retaining unproved properties are expensed.
 
    Unproved oil  and  gas  properties that  are  individually  significant  are
periodically  assessed for impairment of value, and  a loss is recognized at the
time  of  impairment  by  providing  an  impairment  allowance.  Other  unproved
properties  are  amortized  based  on  the  Company's  experience  of successful
drilling and
 
                                      F-8
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
        (THE INFORMATION AND AMOUNTS FOR INTERIM PERIODS ARE UNAUDITED.)
 
(2) SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED)
average holding period. Capitalized costs  of producing oil and gas  properties,
after  considering estimated  dismantlement and abandonment  costs and estimated
salvage values, are depreciated and  depleted by the unit-of-production  method.
Support  equipment and other  property and equipment  are depreciated over their
estimated useful lives.
 
    On sale or retirement of a complete unit of a proved property, the cost  and
related  accumulated  depreciation, depletion,  and amortization  are eliminated
from the property  accounts, and the  resultant gain or  loss is recognized.  On
retirement  or sale of a partial unit of proved property, the cost is charged to
accumulated depreciation, depletion, and amortization  with a resulting gain  or
loss recognized in income.
 
    On  sale of  an entire  interest in  an unproved  property for  cash or cash
equivalent, gain or loss  on the sale is  recognized, taking into  consideration
the  amount  of  any  recorded  impairment if  the  property  had  been assessed
individually. If a partial interest in an unproved property is sold, the  amount
received is treated as a reduction of the cost of the interest retained.
 
    IMPAIRMENT OF LONG-LIVED ASSETS
 
    As  of January 1, 1995,  the Company adopted the  provisions of Statement of
Financial Accounting  Standards No.  121  -- ACCOUNTING  FOR THE  IMPAIRMENT  OF
LONG-LIVED  ASSETS  AND FOR  LONG-LIVED ASSETS  TO BE  DISPOSED OF  ("FAS 121").
Consequently, the Company  reviews its long-lived  assets to be  held and  used,
including  oil and  gas properties  accounted for  under the  successful efforts
method of  accounting,  whenever  events  or  circumstances  indicate  that  the
carrying  value of those  assets may not  be recoverable. An  impairment loss is
indicated if the sum of the expected future cash flows is less than the carrying
amount of the assets. In this circumstance, the Company recognizes an impairment
loss for the amount by which the  carrying amount of the asset exceeds the  fair
value of the asset.
 
    DEFERRED CHARGES
 
    The  Company capitalized certain costs incurred in connection with obtaining
the Credit Agreement and  the related revolver  and term notes  (see Note 7  for
definitions  and descriptions of each). These costs are being amortized over the
lives of the notes.
 
    DEFERRED INCOME
 
    In November 1995, the Company entered  into gas sales agreements whereby  it
committed  to delivery  of a  total of  2,379,000 Mmbtu,  from December  1, 1995
through December 1, 1996, for a total fixed price of $3,429,610. Income from the
agreements is recognized in the period of delivery.
 
    REVENUE RECOGNITION
 
    The Company uses the production method of accounting for crude oil revenues.
To the extent  that crude oil  is produced but  not sold, the  oil in tanks,  if
material,  is recorded as  inventory in the  accompanying consolidated financial
statements.
 
    The Company uses  the sales method  of accounting for  natural gas  revenues
adjusted  for  over and  under produced  amounts  associated with  gas balancing
arrangements. Under this method, revenues are recognized based on actual volumes
of gas sold to purchasers.
 
    Deferred income  associated  with gas  balancing  is accounted  for  on  the
entitlements  method  and represents  amounts received  for  gas sold  under gas
balancing agreements in excess of  the Company's interest in properties  covered
by  such agreements. The Company had $157,785 of deferred income associated with
gas balancing at December 31, 1995. There was no significant deferred income  at
December 31, 1994.
 
                                      F-9
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
        (THE INFORMATION AND AMOUNTS FOR INTERIM PERIODS ARE UNAUDITED.)
 
(2) SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED)
    ENVIRONMENTAL
 
    The  Company is subject to extensive  Federal, state and local environmental
laws and regulations. These  laws, which are  constantly changing, regulate  the
discharge  of  materials into  the environment  and may  require the  Company to
remove or  mitigate the  environmental effects  of the  disposal or  release  of
petroleum  or chemical  substances at various  sites. Environmental expenditures
are  expensed  or  capitalized  depending  on  their  future  economic  benefit.
Expenditures  that relate to an existing condition caused by past operations and
that have no future economic benefits are expensed. Liabilities for expenditures
of a  noncapital  nature  are  recorded  when  environmental  assessment  and/or
remediation is probable, and the costs can be reasonably estimated.
 
    RECLASSIFICATIONS
 
    Certain  reclassifications have  been made  to the  1993 and  1994 financial
statements to conform to the 1995 presentation.
 
    INTERIM FINANCIAL STATEMENTS
 
    The interim financial information  as of March 31,  1996, and for the  three
months  ended March 31, 1995 and 1996,  is unaudited. However, in the opinion of
management,  these  interim  financial  statements  include  all  the  necessary
adjustments  to fairly present the  results of the interim  periods and all such
adjustments are of a normal  recurring nature. The interim financial  statements
should  be read  in conjunction  with the  audited financial  statements for the
years ended December 31, 1993, 1994 and 1995.
 
(3) ACQUISITION OF OIL AND GAS PROPERTIES
    On June 12, 1995, the Company  completed the acquisition of certain oil  and
gas  properties and  related assets from  Parker & Parsley  Development L.P. and
Parker &  Parsley  Producing  L.P.  for  $46,621,371.  The  Company  funded  the
acquisition  under the  Credit Agreement described  in Note (7).  Certain of the
acquired properties,  which  were located  outside  of the  Company's  areas  of
strategic focus, were sold in 1995. No gain or loss was recorded on these sales.
 
(4) IMPAIRMENT OF LONG-LIVED ASSETS
    The  Company  adopted FAS  121  effective as  of  January 1,  1995.  FAS 121
requires that long-lived assets  held and used by  an entity, including oil  and
gas  properties accounted for under the successful efforts method of accounting,
be reviewed for impairment whenever events or changes in circumstances  indicate
that  the carrying amount of an asset  may not be recoverable. Long-lived assets
to be disposed of  are to be accounted  for at the lower  of carrying amount  or
fair  value less cost to sell when management has committed to a plan to dispose
of  the  assets.  All  companies,  including  successful  efforts  oil  and  gas
companies,  are  required to  adopt  FAS 121  for  fiscal years  beginning after
December 15, 1995.
 
    In order  to  determine whether  an  impairment had  occurred,  the  Company
estimated  the expected  future cash  flows of  its oil  and gas  properties and
compared such  future cash  flows to  the carrying  amount of  the oil  and  gas
properties  to determine if  the carrying amount was  recoverable. Based on this
process, no writedown in the carrying amount of the Company's proved  properties
was necessary at December 31, 1995.
 
(5) DERIVATIVE FINANCIAL INSTRUMENTS
    The Company utilizes derivative financial instruments to manage well-defined
interest rate and commodity price risks. The Company is exposed to credit losses
in  the event of nonperformance by the  counterparties to its interest rate swap
agreements and its commodity hedges. The Company anticipates, however, that such
counterparties will  be  able  to  fully satisfy  their  obligations  under  the
contracts.  The Company does not obtain  collateral or other security to support
financial instruments subject to credit risk but monitors the credit standing of
the counterparties.
 
                                      F-10
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
        (THE INFORMATION AND AMOUNTS FOR INTERIM PERIODS ARE UNAUDITED.)
 
(5) DERIVATIVE FINANCIAL INSTRUMENTS (CONTINUED)
    COMMODITY HEDGES.  The Company utilizes option contracts to hedge the effect
of price changes  on future  oil and gas  production. The  following table  sets
forth the future volumes hedged by year and the weighted-average strike price of
the option contracts at December 31, 1995:
 
<TABLE>
<CAPTION>
                                                             OIL         GAS
                                                            VOLUME      VOLUME        STRIKE PRICE
                                                            (BBLS)     (MMBTU)       PER BBL/MMBTU
                                                          ----------  ----------  --------------------
<S>                                                       <C>         <C>         <C>
Oil:
  1996..................................................   1,830,000          --   $16.00 - $20.38(a)
  1997..................................................     912,500          --   $16.00 - $20.65(a)
Gas:
  1996..................................................          --   1,500,000        $1.65(b)
  1997..................................................          --   1,350,000        $1.65(b)
</TABLE>
 
- ------------------------
(a) Represents  the  weighted-average  price  of  collars  established  with the
    purchase of put option contracts and the sale of call option contracts.
 
(b) Represents the strike price on purchased put option contracts.
 
    INTEREST RATE  SWAP AGREEMENTS.   The  Company utilizes  interest rate  swap
agreements  to reduce  the potential  impact of  increases in  interest rates on
floating-rate, long-term debt. At December 31, 1995, the Company was a party  to
two  interest rate swap agreements, providing  the Company with a fixed interest
rate for the terms of the agreements. The following table sets forth the  terms,
fixed  rates, and notional amounts of the agreements in place as of December 31,
1995:
 
<TABLE>
<CAPTION>
                                      NOTIONAL
                                      PRINCIPAL                FIXED
               TERM                    AMOUNT              INTEREST RATE
- ----------------------------------  -------------  ------------------------------
<S>                                 <C>            <C>
Jan. 25, 1996 to Jan. 25, 1999       $24 million     ranging from 7.5% to 8.5%
May 24, 1995 to May 27, 1997         $60 million               5.99%
</TABLE>
 
(6) FAIR VALUE OF FINANCIAL INSTRUMENTS
    The following table presents the carrying amounts and estimated fair  values
of  the  Company's financial  instruments at  December 31,  1994 and  1995. FASB
Statement No.  107,  DISCLOSURES  ABOUT FAIR  VALUE  OF  FINANCIAL  INSTRUMENTS,
defines  the fair  value of a  financial instrument  as the amount  at which the
instrument could be exchanged in a current transaction between willing parties.
 
<TABLE>
<CAPTION>
                                                                                1994                  1995
                                                                        --------------------  --------------------
                                                                        CARRYING     FAIR     CARRYING     FAIR
                                                                         AMOUNT      VALUE     AMOUNT      VALUE
                                                                        ---------  ---------  ---------  ---------
<S>                                                                     <C>        <C>        <C>        <C>
                                                                                     ($ IN THOUSANDS)
Financial assets:
  Cash, cash equivalents and restricted cash..........................  $     137  $     137  $   2,866  $   2,866
  Receivables (trade).................................................      1,042      1,042      3,154      3,154
  Receivables (oil and gas sales).....................................      1,715      1,715      3,915      3,915
  Commodity option contracts..........................................         --         --        165        555
  Interest rate swap and option agreements............................        203         --        146     (2,970)
  Notes receivable -- affiliate.......................................        390        390        684        684
Financial liabilities:
  Payables (trade)....................................................      1,712      1,712      5,467      5,467
  Deferred income.....................................................         --         --      3,319      2,950
  Long-term debt......................................................     23,613     23,613     71,494     71,494
</TABLE>
 
                                      F-11
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
        (THE INFORMATION AND AMOUNTS FOR INTERIM PERIODS ARE UNAUDITED.)
 
(6) FAIR VALUE OF FINANCIAL INSTRUMENTS (CONTINUED)
    The carrying amounts  shown in the  table are included  in the statement  of
financial position under the indicated captions.
 
    The  following methods and assumptions were  used to estimate the fair value
of each class of financial instruments:
 
    CASH,  TRADE  RECEIVABLES,  AND  TRADE  PAYABLES:    The  carrying   amounts
approximate fair value because of the short maturity of those instruments.
 
    OTHER  CURRENT ASSETS:  The amounts  reported relate to the commodity option
contracts and interest rate  swap agreements described in  Note 5. The  carrying
amount comprises the unamortized premiums paid for the contracts. The fair value
is  estimated using option  pricing models and  essentially values the potential
for the  contracts and  agreements  to become  in-the-money through  changes  in
commodity prices and interest rates during the remaining terms.
 
    NOTES RECEIVABLE-AFFILIATE:  The amounts reported relate to notes receivable
from  an affiliated company. The carrying amount approximates fair value because
the rate given  to the affiliate  company is not  materially different from  the
affiliate company's bank debt.
 
    DEFERRED INCOME:  The amounts reported relate to the gas purchase agreements
described  in Note 2. The carrying amount represents the payments received under
the agreements for  which subsequent  delivery is  required. The  fair value  is
estimated  based upon the  commodity price at  December 31, 1995,  for a similar
agreement.
 
    LONG-TERM DEBT:  The fair value of the Company's long-term debt is estimated
by discounting expected cash flows at the rates currently offered to the Company
for debt of the same remaining maturities, as advised by the Company's bankers.
 
(7) LONG-TERM DEBT
    Long-term debt consists of the following (in thousands):
 
<TABLE>
<CAPTION>
                                                                              DECEMBER 31,
                                                                          --------------------
                                                                            1994       1995
                                                                          ---------  ---------
<S>                                                                       <C>        <C>
Revolver note...........................................................  $      --  $  59,824
Term notes..............................................................         --     11,670
Note payable to bank....................................................     23,591         --
Note payable to member..................................................         22         --
                                                                          ---------  ---------
                                                                             23,613     71,494
    Less current maturities.............................................         22         --
                                                                          ---------  ---------
                                                                          $  23,591  $  71,494
                                                                          ---------  ---------
                                                                          ---------  ---------
</TABLE>
 
    At December  31, 1995,  the  Company and  certain  of its  subsidiaries  are
parties  to a  Credit Agreement  with a  syndicate of  banks (the  "Banks"). The
Credit Agreement provides for an aggregate $185 million senior secured revolving
line of credit  ("Revolver Notes")  and an aggregate  of $15  million in  senior
secured  term notes ("Term Notes"). All notes are secured with the assets of the
Company and  are guaranteed  by the  Company's subsidiaries  and, to  a  limited
extent, its individual members.
 
    The  Revolver Notes  and Term  Notes are  subject to  an aggregate borrowing
base, as determined by the Banks or their agents in their sole discretion and is
redetermined at least bi-annually  as of January 15  and July 15, utilizing  oil
and  gas reserve information as  of the immediately preceding  period end. As of
January 15, 1996, the borrowing base was $71,670,000.
 
                                      F-12
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
        (THE INFORMATION AND AMOUNTS FOR INTERIM PERIODS ARE UNAUDITED.)
 
(7) LONG-TERM DEBT (CONTINUED)
    All outstanding balances under  the Credit Agreement  may be designated,  at
the  Company's option, as  either "Base Rate Portions"  or "Fixed Rate Portions"
(both as  defined in  the Credit  Agreement), provided  that no  more than  five
Eurodollar  Tranches may be outstanding  at any time. The  Base Rate Portions of
the Revolver Notes bear interest at  the fluctuating Base Rate, plus a  Revolver
Base  Rate Spread  ranging from 0.25%  to 0.75%, depending  upon the outstanding
principal balances of the Term Notes. The  Base Rate Portions of the Term  Notes
bear  interest at the fluctuating Base Rate  plus 0.75%. The Fixed Rate Portions
of the Revolver Notes bear interest at the Eurodollar Rate for a fixed period of
time elected by  the Company,  plus a Revolver  Fixed Rate  Spread ranging  from
2.25%  to 3.00%,  depending on  the outstanding  principal balances  of the Term
Notes. The Fixed Rate Portions of the Term Notes bear interest at the Eurodollar
Rate for a fixed period of time elected by the Company, plus a Fixed Rate Spread
of 3.00%. As of December 31, 1995, the Company had elected a fixed rate of 8.82%
for the Revolver Notes and had elected  fixed rates ranging from 8.82% to  8.94%
for  $14,000,000  of  the  outstanding  Term Notes  at  December  31,  1995. The
remaining balances  of  the  Term  Notes  bear interest  at  the  Base  Rate  of
NationsBank Prime plus 1.50% at December 31, 1995.
 
    The  outstanding principal balance of the  Revolver Notes is due and payable
in sixty  (60) monthly  installments beginning  August 1,  1996, and  continuing
regularly  thereafter until July  1, 2001. The  outstanding principal balance of
the Term Notes is due and payable  in two (2) installments, each of which  shall
be  equal to one-half of  the unpaid principal balance of  each note, on July 1,
1996, and January 1, 1997.
 
    The Credit Agreement requires the Company to hedge not less than 60% of  the
Company's  total  sales  volume,  through December  31,  1997,  from  its proved
developed producing oil and gas  reserves, with a floor  price of not less  than
$16 per Bbl of oil or $1.50 per Mcf of gas.
 
    Additionally,  the Credit  Agreement contains  various restrictive covenants
and compliance requirements,  which include: (a)  restrictions on dividends  and
the  incurrence of additional indebtedness; (b)  restrictions as to merger, sale
or transfer of  assets; (c) limiting  total lease payments  and total  aggregate
executive  compensation to  $750,000 and  $500,000, respectively,  in any fiscal
year; and (d) compliance with certain financial ratios.
 
    The  Company  was   in  violation  of   certain  covenants  and   compliance
requirements  as of  December 31,  1995. Subsequent  to December  31, 1995, such
violations were waived by the Banks.
 
    Maturities of  long-term debt  at  December 31,  1995,  are as  follows  (in
thousands):
 
<TABLE>
<S>                                                          <C>
1996.......................................................  $  10,820
1997.......................................................     17,800
1998.......................................................     11,965
1999.......................................................     11,965
2000.......................................................     11,965
Thereafter.................................................      6,979
</TABLE>
 
    The  Company paid  interest on  long-term debt  of $546,147,  $1,356,604 and
$4,453,684 in 1993, 1994 and 1995, respectively.
 
    As described in Note 12,  on June 10, 1996, the  Company entered into a  new
loan agreement, proceeds of which were used to repay the existing notes.
 
                                      F-13
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
        (THE INFORMATION AND AMOUNTS FOR INTERIM PERIODS ARE UNAUDITED.)
 
(8) COMMITMENTS AND CONTINGENCIES
 
    LEASES
 
    The Company leases equipment and office facilities under operating leases on
which  rental expense for the years ended  December 31, 1993, 1994 and 1995, was
$110,023, $197,533 and $311,221, respectively. Future minimum lease  commitments
under  noncancellable operating leases at December  31, 1995, are as follows (in
thousands):
 
<TABLE>
<S>                                                           <C>
1996........................................................  $     257
1997........................................................        272
1998........................................................        268
1999........................................................        195
2000........................................................        188
Thereafter..................................................      1,190
</TABLE>
 
    SEVERANCE AGREEMENTS
 
    On February 17, 1995,  the Company entered  into employment agreements  with
each  of the officers which  are effective from the  above date through February
17, 2000, or  until terminated by  the officer  or the Company.  In addition  to
providing  a  base salary  and nominal  yearly increases  for each  officer, the
employment agreements provide  for severance  payments upon  termination of  any
such officer's employment or a significant reduction in that officer's duties or
responsibilities.
 
    In  the event  of such a  termination, the  Company is obligated  to pay the
officer an  amount  equal  to the  present  value  (discounted at  10%)  of  the
officer's  salary  which would  have been  paid through  February 17,  2000. The
current annual  base salaries  for the  officers covered  under such  employment
agreements total approximately $500,000.
 
    EXPLORATION AND DEVELOPMENT
 
    On July 6, 1995, the Company, entered into an agreement with an unaffiliated
third  party which  had previously  obtained a  concession from  the Republic of
Moldova whereby the Company committed to  develop several oil and gas fields  in
the  Republic of  Moldova, commencing  in 1995, and  embark on  a multi-year 400
kilometer seismic survey, beginning in 1996, in exchange for the exclusive right
to develop and  explore for  oil and  gas in  the Republic  of Moldova.  Through
December  31, 1995, the  Company has incurred $214,178  in connection with these
activities.
 
    LETTERS OF CREDIT
 
    As a result of certain bonding and trade creditor requirements, the  Company
has  caused  irrevocable letters  of  credit to  be  issued by  a  bank totaling
$106,000. As of December 31, 1995, no amounts had been drawn on these letters of
credit.
 
(9) 401(K) PLAN
    The Company has established a  qualified cash or deferred arrangement  under
IRS  code section 401(k)  covering substantially all  employees. Under the plan,
the employees have  an option  to make elective  contributions of  a portion  of
their  eligible compensation, not to exceed specified annual limitations, to the
plan and the  Company has  an option  to match  a percentage  of the  employee's
contribution.  The Company has made matching  contributions to the plan totaling
$16,950, $8,921 and $22,531 in 1993, 1994 and 1995, respectively.
 
(10) REDEEMABLE MEMBERS' CAPITAL AND MEMBERS' CAPITAL
    During  1995,  NationsBank  Capital  Corporation  ("NBCC")  contributed  $10
million  in exchange for a  30% ownership interest in  the Company including the
preferential return described below. The Company incurred $751,737 in legal fees
and broker's commissions in connection with this transaction and recorded  these
costs as direct charges to members' capital in 1995.
 
                                      F-14
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
        (THE INFORMATION AND AMOUNTS FOR INTERIM PERIODS ARE UNAUDITED.)
 
(10) REDEEMABLE MEMBERS' CAPITAL AND MEMBERS' CAPITAL (CONTINUED)
    Redeemable  members' capital is subject to  a preferential return of 15% per
annum and  is redeemable  at any  time at  the Company's  option, subject  to  a
redemption  premium as described below, or at NBCC's option on February 17, 2003
or at an earlier date  upon occurrence of certain  events including a change  in
control,  certain changes in management,  a change in the  Company's status as a
limited liability company for tax purposes, or violation of any of various other
restrictive provisions contained in the  Regulations of Costilla Energy,  L.L.C.
(the  "Regulations").  The 15%  preferred return  is treated  as a  reduction of
members' capital. The redemption price to be paid by the Company shall be  equal
to  the  initial  amount  received  for  the  preferred  units  plus  a premium,
determined in the year the units are purchased, as follows:
 
<TABLE>
<CAPTION>
      YEAR AFTER            PREMIUM
   FEBRUARY 17, 1995      PERCENTAGE
- -----------------------  -------------
<S>                      <C>
               1                  10%
               2                  10%
               3                   8%
               4                   6%
               5                   4%
               6                   2%
               7                   0%
               8                   0%
</TABLE>
 
    NBCC's 30% members' interest may be repurchased by the Company to the extent
the Company has exercised its right to redeem all or a portion of the redeemable
members' capital or  the Company  may be  required to  purchase NBCC's  members'
capital  upon the occurrence of certain events similar to those events requiring
redemption of the redeemable  members' capital described above,  but not on  any
specified  date in  the future.  The redemption price  the Company  would pay is
determined by the year in which the members' capital is repurchased, as follows:
 
<TABLE>
<CAPTION>
                                                                       AGGREGATE
BEFORE FEBRUARY 17                                                  REDEMPTION PRICE
- ------------------------------------------------------------------  ----------------
<S>                                                                 <C>
1996..............................................................    $          1
1997..............................................................       1,500,000
1998..............................................................       3,000,000
1999..............................................................       4,500,000
2000..............................................................       5,500,000
</TABLE>
 
    At December 31, 1995,  the Company was in  violation of various  restrictive
provisions of the Regulations. Subsequent to December 31, 1995, NBCC waived such
violations.
 
(11) RELATED PARTY TRANSACTIONS
    Certain  members  and officers  of  the Company  own  interests in  and hold
positions with  A&P  Meter Service  and  Supply, Inc.  ("A&P"),  CSL  Management
Corporation  ("CSL"),  511 Tex  L.C. ("511  Tex")  and Valley  Gathering Company
("Valley").
 
    Advances from the Company to A&P have been consolidated into two  promissory
notes.  The first note, which was  originally executed December 31, 1994, totals
$390,000, including accrued interest of $20,000  at December 31, 1995. The  note
bears  interest  at a  floating rate  equal to  the "prime  rate" plus  1.0%. No
principal or  interest  payments are  due  until the  maturity  of the  note  at
December  31,  2004. The  note is  secured by  a second  lien on  A&P's accounts
receivable, inventory  and  equipment. The  second  note  is in  the  amount  of
$294,000,  including accrued interest of $47,000, and is dated May 22, 1996. The
note bears interest at 6.0% per annum, is unsecured and is payable upon  demand.
During 1995, the Company paid $612,139 to A&P for goods and services provided.
 
                                      F-15
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
        (THE INFORMATION AND AMOUNTS FOR INTERIM PERIODS ARE UNAUDITED.)
 
(11) RELATED PARTY TRANSACTIONS (CONTINUED)
    During  1993,  1994  and  1995,  the  Company  paid  $312,623,  $549,620 and
$592,920, respectively,  to  CSL  for  management fees  and  lease  payments  on
equipment.
 
    During 1995, the Company paid $67,896 to 511 Tex for office rent.
 
    During 1994 and 1995, the Company paid $2,458 and $440,884, respectively, to
Valley  for gas compression and salt water disposal charges. During 1995, Valley
paid the Company $109,399 for operating  costs of its salt water disposal  wells
and gas compressors.
 
(12) SUBSEQUENT EVENTS
    On  March 8, 1996, the  Company executed a Purchase  and Sale Agreement with
Parker and Parsley Petroleum Company to  acquire certain oil and gas  properties
for  an  estimated adjusted  purchase price  of  approximately $40  million. The
properties are located primarily in south and west Texas. The acquisition closed
on June 14, 1996.
 
    In connection  with the  foregoing,  the Company  entered  into a  new  loan
agreement  with  NationsBridge L.L.C.,  an  affiliate of  the  Company's current
lender, to provide financing  of up to $125  million in advances (the  "Loans"),
subject to certain terms and conditions. Proceeds of the Loans were used to fund
the  Acquisition, to  refinance substantially  all of  the Company's outstanding
indebtedness, and for other general corporate purposes.
 
    Advances under the Loans were to be  made in two portions, Tranche A was  up
to  $95,000,000  and  Tranche  B  was  $30,000,000.  Tranche  A  initially bears
interest, at the Company's option, at  the applicable prime rate ("Prime")  plus
0.75%  or LIBOR plus 3.0%. Each margin  above Prime and LIBOR increases by 0.50%
at the end of each successive three-month  period, up to a maximum of 2.75%  and
5.0%  for Prime and  LIBOR, respectively. Tranche B  initially bears interest at
14.00% per annum,  increasing 0.50% at  the end of  each successive  three-month
period, up to a maximum of 16.5%.
 
    Tranche  A loans are subject to  a borrowing base determination. The initial
borrowing base is $95,000,000 which  is automatically reduced by $3,000,000  per
quarter  beginning  January  1, 1997.  The  borrowing  base is  also  subject to
periodic redetermination by NationsBridge L.L.C.  based on its determination  of
the  collateral value of the Company's oil and gas properties. Final maturity of
loans made under Tranches A and B is June 10, 1999.
 
    The Loans  are secured  by first  priority liens,  assignments and  security
interests  in all oil and gas properties, pipelines and gathering systems of the
Company and stock  of the  Company's subsidiaries. Additionally,  the Loans  are
subject  to various restrictive covenants and compliance requirements, including
but not  limited  to  (a)  restrictions  on  dividends  and  the  incurrence  of
additional  indebtedness, (b) minimum limitations on the Company's current ratio
and tangible net  worth, (c) limitations  on payments for  leases and  executive
compensation,  (d) maximum  limitations on general  and administrative expenses,
capital expenditures and the Company's ratio of debt to adjusted cash flow,  and
(e)  a requirement to pay to the lender all net oil and gas revenues (as defined
and as adjusted for capital expenditures) on a quarterly basis.
 
    The Company paid the lender's fees and expenses in connection with obtaining
the Loans.  The fees  were  approximately $2,625,000  and  will increase  by  an
additional  $625,000 if the Tranche B Loans  remain outstanding for more than 90
days. In addition, if the Tranche B  amounts are not repaid within one year,  an
additional amount of $4,800,000 will accrue.
 
                                      F-16
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
        (THE INFORMATION AND AMOUNTS FOR INTERIM PERIODS ARE UNAUDITED.)
 
(13) OIL AND GAS EXPENDITURES
    The  following  table  reflects  costs  incurred  in  oil  and  gas property
acquisition, exploration and development activities:
 
<TABLE>
<CAPTION>
                                                                       YEARS ENDED DECEMBER 31,       THREE MONTHS
                                                                    -------------------------------  ENDED MARCH 31,
                                                                      1993       1994       1995          1996
                                                                    ---------  ---------  ---------  ---------------
<S>                                                                 <C>        <C>        <C>        <C>
                                                                            (IN THOUSANDS)
Property acquisition costs:
  Proved..........................................................  $   4,665  $   9,649  $  52,470     $   2,246
  Unproved........................................................        829      1,232      1,742           677
Exploration.......................................................      2,017      2,167      5,627         1,822
Development.......................................................         --         --        158           232
                                                                    ---------  ---------  ---------        ------
                                                                    $   7,511  $  13,048  $  59,997     $   4,977
                                                                    ---------  ---------  ---------        ------
                                                                    ---------  ---------  ---------        ------
</TABLE>
 
(14) SUPPLEMENTAL OIL AND GAS RESERVE INFORMATION (UNAUDITED)
    The estimates of proved oil and gas reserves, which are located  principally
in the United States, were prepared by the Company as of December 31, 1993, 1994
and  1995, and Williamson  Petroleum Consultants as of  March 31, 1996. Reserves
were estimated in  accordance with guidelines  established by the  SEC and  FASB
which  require that  reserve estimates be  prepared under  existing economic and
operating conditions with no provision for price and cost escalations, except by
contractual arrangements.  The  Company  has  presented  the  reserve  estimates
utilizing  an oil price of $17.79 per Bbl and a gas price of $2.03 per Mcf as of
December 31, 1995, and an oil price of  $20.71 per Bbl and a gas price of  $2.00
per Mcf as of March 31, 1996.
 
                                      F-17
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
                         NOTES TO FINANCIAL STATEMENTS
        (THE INFORMATION AND AMOUNTS FOR INTERIM PERIODS ARE UNAUDITED.)
 
(14) SUPPLEMENTAL OIL AND GAS RESERVE INFORMATION (UNAUDITED)
 
    OIL AND GAS PRODUCING ACTIVITIES
 
    Oil and gas reserve quantity estimates are subject to numerous uncertainties
inherent  in  the  estimation  of  quantities  of  proved  reserves  and  in the
projection  of  future  rates  of  production  and  the  timing  of  development
expenditures.  The accuracy of  such estimates is  a function of  the quality of
available data and  of engineering and  geological interpretation and  judgment.
Results  of subsequent drilling, testing and  production may cause either upward
or downward revision of previous  estimates. Further, the volumes considered  to
be  commercially  recoverable fluctuate  with  changes in  prices  and operating
costs. The Company  emphasizes that reserve  estimates are inherently  imprecise
and that estimates of new discoveries are more imprecise than those of currently
producing  oil and gas properties. Accordingly,  these estimates are expected to
change as additional information becomes available in the future.
 
<TABLE>
<CAPTION>
                                                                                 OIL AND CONDENSATE        GAS
                                                                                       (MBBLS)           (MMCF)
                                                                                 -------------------  -------------
<S>                                                                              <C>                  <C>
Total Proved Reserves:
Balance, January 1, 1993.......................................................           1,985            16,418
  Revisions of previous estimates..............................................              57             1,160
  Extensions and discoveries...................................................             380               591
  Production...................................................................            (158)             (865)
  Purchases of minerals-in-place...............................................             101             4,315
                                                                                         ------            ------
Balance, December 31, 1993.....................................................           2,365            21,619
  Revisions of previous estimates..............................................            (460)           (5,424)
  Extensions and discoveries...................................................             761             1,520
  Production...................................................................            (330)           (1,600)
  Purchases of minerals-in-place...............................................           1,673            11,397
                                                                                         ------            ------
Balance, December 31, 1994.....................................................           4,009            27,512
  Revisions of previous estimates..............................................            (570)              425
  Extensions and discoveries...................................................             605             8,922
  Production...................................................................            (950)           (4,806)
  Purchases of minerals-in-place...............................................           7,694            46,099
                                                                                         ------            ------
Balance, December 31, 1995.....................................................          10,788            78,152
  Revisions of previous estimates..............................................             437             2,615
  Extensions and discoveries...................................................             592               296
  Production...................................................................            (338)           (1,643)
  Purchases of minerals-in-place...............................................              --                --
                                                                                         ------            ------
Balance, March 31, 1996........................................................          11,479            79,420
                                                                                         ------            ------
                                                                                         ------            ------
Proved Developed Reserves:
  January 1, 1993..............................................................           1,488            10,055
  December 31, 1993............................................................           1,785            13,268
  December 31, 1994............................................................           2,632            16,340
  December 31, 1995............................................................           8,566            57,393
  March 31, 1996...............................................................           9,037            55,408
</TABLE>
 
    STANDARDIZED MEASURE OF DISCOUNTED FUTURE NET CASH FLOWS RELATING TO PROVED
OIL AND GAS RESERVES
 
    The standardized measure of discounted future net cash flows is computed  by
applying  year-end prices  of oil and  gas (with consideration  of price changes
only to the extent provided by contractual arrangements)
 
                                      F-18
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
                         NOTES TO FINANCIAL STATEMENTS
        (THE INFORMATION AND AMOUNTS FOR INTERIM PERIODS ARE UNAUDITED.)
 
(14) SUPPLEMENTAL OIL AND GAS RESERVE INFORMATION (UNAUDITED) (CONTINUED)
to the  estimated  future  production  of proved  oil  and  gas  reserves,  less
estimated  future  expenditures  (based on  year-end  costs) to  be  incurred in
developing and producing the proved  reserves, less estimated future income  tax
expenses  (based on year-end  statutory tax rates,  with consideration of future
tax rates already legislated) to be incurred on pretax net cash flows, less  tax
basis  of the  properties and  available credits,  and assuming  continuation of
existing economic  conditions. The  estimated  future net  cash flows  are  then
discounted  using a rate of 10% per year  to reflect the estimated timing of the
future cash flows.
 
    Discounted future  cash  flow  estimates  like those  shown  below  are  not
intended  to represent estimates  of the fair  value of oil  and gas properties.
Estimates of  fair value  should also  consider probable  reserves,  anticipated
future oil and gas prices, interest rates, changes in development and production
costs  and risks associated  with future production. Because  of these and other
considerations, any  estimate  of  fair  value  is  necessarily  subjective  and
imprecise.
 
<TABLE>
<CAPTION>
                                                                                                   THREE MONTHS
                                                                  YEARS ENDED DECEMBER 31,        ENDED MARCH 31,
                                                             -----------------------------------  ---------------
                                                                1993        1994        1995           1996
                                                             ----------  ----------  -----------  ---------------
                                                                                (IN THOUSANDS)
<S>                                                          <C>         <C>         <C>          <C>
Future cash flows..........................................  $   83,510  $  122,098  $   350,653    $   396,919
Future costs:
  Production...............................................     (31,811)    (46,345)    (145,510)      (162,146)
  Development..............................................      (4,486)     (7,157)     (16,806)       (17,975)
                                                             ----------  ----------  -----------  ---------------
Future net cash flows......................................      47,213      68,596      188,337        216,798
10% annual discount for estimated timing of cash flows.....     (20,836)    (31,817)     (75,041)       (87,707)
                                                             ----------  ----------  -----------  ---------------
Standardized measure of discounted net cash flows..........  $   26,377  $   36,779  $   113,296    $   129,091
                                                             ----------  ----------  -----------  ---------------
                                                             ----------  ----------  -----------  ---------------
</TABLE>
 
    CHANGES IN STANDARDIZED MEASURE OF DISCOUNTED FUTURE NET CASH FLOWS FROM
PROVED RESERVES
 
<TABLE>
<CAPTION>
                                                                                                   THREE MONTHS
                                                                    YEARS ENDED DECEMBER 31,      ENDED MARCH 31,
                                                                --------------------------------  ---------------
                                                                  1993       1994        1995          1996
                                                                ---------  ---------  ----------  ---------------
                                                                                 (IN THOUSANDS)
<S>                                                             <C>        <C>        <C>         <C>
Increase (decrease):
  Purchase of minerals-in-place...............................  $   3,732  $  15,231  $   77,343    $        --
  Extensions and discoveries and improved recovery, net of
   future production and development costs....................      2,707      4,072       9,799          6,002
  Accretion of discount.......................................      2,056      2,638       3,678          2,832
  Net change in sales prices, net of production costs.........       (209)       503      (3,422)         9,229
  Changes in estimated future development costs...............        (16)       940      (2,419)          (235)
  Revisions of quantity estimates.............................      1,203     (7,248)     (2,855)         4,839
  Sales, net of production costs..............................     (2,543)    (5,286)    (11,338)        (5,174)
  Changes of production rates (timing) and other..............     (1,114)      (448)      5,731         (1,698)
                                                                ---------  ---------  ----------  ---------------
    Net increase..............................................      5,816     10,402      76,517         15,795
Standardized measure of discounted future net cash flows:
    Beginning of period.......................................     20,561     26,377      36,779        113,296
                                                                ---------  ---------  ----------  ---------------
    End of period.............................................  $  26,377  $  36,779  $  113,296    $   129,091
                                                                ---------  ---------  ----------  ---------------
                                                                ---------  ---------  ----------  ---------------
</TABLE>
 
                                      F-19
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
                         NOTES TO FINANCIAL STATEMENTS
        (THE INFORMATION AND AMOUNTS FOR INTERIM PERIODS ARE UNAUDITED.)
 
(14) SUPPLEMENTAL OIL AND GAS RESERVE INFORMATION (UNAUDITED) (CONTINUED)
 
    The  1995  future cash  flows shown  above  include amounts  attributable to
proved undeveloped  reserves requiring  approximately  $15.0 million  of  future
development costs. If these reserves are not developed, the standardized measure
of  discounted future net  cash flows for  1995 shown above  would be reduced by
approximately $22.4 million.
 
                                      F-20
<PAGE>
                          INDEPENDENT AUDITORS' REPORT
 
The Members
Costilla Energy, L.L.C.:
 
    We have audited the accompanying statements of revenues and direct operating
expenses of the 1995 Acquisition (see Note  1) for the years ended December  31,
1993  and 1994,  and the period  ended June  12, 1995. These  statements are the
responsibility of the Company's management. Our responsibility is to express  an
opinion on these statements based on our audits.
 
    We  conducted  our audits  in  accordance with  generally  accepted auditing
standards. Those standards require that we plan and perform the audit to  obtain
reasonable  assurance  about  whether  the  statements  of  revenues  and direct
operating  expenses  are  free  of  material  misstatement.  An  audit  includes
examining,  on a test basis, evidence  supporting the amounts and disclosures in
the financial  statements.  An  audit also  includes  assessing  the  accounting
principles  used  and  significant  estimates made  by  management,  as  well as
evaluating the  overall  statement  presentation. We  believe  that  our  audits
provide a reasonable basis for our opinion.
 
    The  accompanying statements of revenues  and direct operating expenses were
prepared for the  purpose of  complying with the  rules and  regulations of  the
Securities  and  Exchange Commission  (for inclusion  in  Forms S-1  of Costilla
Energy, Inc. as  described in  Note 1)  and are not  intended to  be a  complete
presentation of the 1995 Acquisition interests' revenue and expenses.
 
    In  our opinion,  the statements of  revenues and  direct operating expenses
referred to above  present fairly, in  all material respects,  the revenues  and
direct  operating expenses of the 1995  Acquisition for the years ended December
31, 1993  and 1994,  and the  period ended  June 12,  1995, in  conformity  with
generally accepted accounting principles.
 
                                          KPMG PEAT MARWICK LLP
 
Midland, Texas
July 4, 1996
 
                                      F-21
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
                                1995 ACQUISITION
 
              STATEMENTS OF REVENUES AND DIRECT OPERATING EXPENSES
                                 (IN THOUSANDS)
 
<TABLE>
<CAPTION>
                                                                                  YEARS ENDED
                                                                                  DECEMBER 31,
                                                                              --------------------   PERIOD ENDED
                                                                                1993       1994     JUNE 12, 1995
                                                                              ---------  ---------  --------------
<S>                                                                           <C>        <C>        <C>
Revenues:
  Oil and condensate........................................................  $  18,542  $  16,217    $    7,572
  Natural gas...............................................................     13,780     11,407         3,358
                                                                              ---------  ---------       -------
                                                                                 32,322     27,624        10,930
Direct operating expenses:
  Lease operating...........................................................     13,376     11,220         4,550
  Workovers and dry hole costs..............................................        462        470           109
  Production taxes..........................................................      2,070      2,023           923
                                                                              ---------  ---------       -------
                                                                                 15,908     13,713         5,582
                                                                              ---------  ---------       -------
Revenues in excess of direct operating expenses.............................  $  16,414  $  13,911    $    5,348
                                                                              ---------  ---------       -------
                                                                              ---------  ---------       -------
</TABLE>
 
                See the accompanying notes to these statements.
 
                                      F-22
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
                                1995 ACQUISITION
 
       NOTES TO THE STATEMENTS OF REVENUES AND DIRECT OPERATING EXPENSES
 
(1) BASIS OF PRESENTATION
    On June 12, 1995, Costilla Energy, L.L.C. and Costilla Petroleum Corporation
(collectively,  the "Company") acquired  from Parker &  Parsley Development L.P.
and Parker & Parsley Producing  L.P. (collectively, "Parker & Parsley")  certain
oil   and  gas  properties   (the  "1995  Acquisition")   for  $46,621,371.  The
accompanying statements of revenues and  direct operating expenses for the  1995
Acquisition  do not include general and administrative expenses, interest income
or expense, a  provision for  depreciation, depletion and  amortization, or  any
provision  for income taxes since historical expenses of this nature incurred by
Parker & Parsley are not necessarily indicative  of the costs to be incurred  by
the Company.
 
    Historical  financial information reflecting  financial position, results of
operations, and cash flows  of the 1995 Acquisition,  are not presented  because
the  purchase price was assigned to the oil and gas property interests acquired.
Other assets acquired  and liabilities assumed  were not material.  Accordingly,
the  historical statements of revenues and direct operating expenses of the 1995
Acquisition are presented  in lieu  of the financial  statements required  under
Rule 3-05 of Securities and Exchange Commission Regulation S-X.
 
    Revenues  in the  accompanying statements  of revenues  and direct operating
expenses are  recognized on  the  sales method.  Direct operating  expenses  are
recognized on the accrual method.
 
(2) SUPPLEMENTARY FINANCIAL INFORMATION FOR OIL AND GAS PRODUCING ACTIVITIES
(UNAUDITED)
 
    ESTIMATED QUANTITIES OF PROVED OIL AND GAS RESERVES
 
    Reserve  information presented  below for the  1995 Acquisition  is based on
Company prepared reserve estimates, using prices and costs in effect at December
31, 1993  and 1994,  and the  period ended  June 12,  1995. Changes  in  reserve
estimates  were derived  by adjusting the  period-end quantities  and values for
actual production using historical prices and costs.
 
    Proved reserves are estimated quantities of crude oil and natural gas  which
geological  and  engineering data  demonstrate with  reasonable certainty  to be
recoverable in future years  from known reservoirs  under existing economic  and
operating  conditions. Proved developed reserves are those which are expected to
be recovered  through  existing  wells with  existing  equipment  and  operating
methods.  Oil  and  gas  reserve  quantity  estimates  are  subject  to numerous
uncertainties inherent in the estimation of quantities of proved reserves and in
the projection  of future  rates of  production and  the timing  of  development
expenditures.  The accuracy of  such estimates is  a function of  the quality of
available data and  of engineering and  geological interpretation and  judgment.
Results  of subsequent drilling, testing and  production may cause either upward
or downward revision of previous  estimates. Further, the volumes considered  to
be  commercially  recoverable fluctuate  with  changes in  prices  and operating
costs. The Company  emphasizes that reserve  estimates are inherently  imprecise
and that estimates of new discoveries are more imprecise than those of currently
producing  oil  and gas  properties.  Accordingly, these  reserve  estimates are
expected to change as additional information becomes available in the future.
 
                                      F-23
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
                                1995 ACQUISITION
 
 NOTES TO THE STATEMENTS OF REVENUES AND DIRECT OPERATING EXPENSES (CONTINUED)
 
(2) SUPPLEMENTARY FINANCIAL INFORMATION FOR OIL AND GAS PRODUCING ACTIVITIES
(UNAUDITED)
    (CONTINUED)
    Below are  the  net  estimated  quantities of  proved  reserves  and  proved
developed reserves for the 1995 Acquisition.
 
<TABLE>
<CAPTION>
                                                                      OIL (MBBLS)    GAS (MMCF)
                                                                     -------------  -------------
<S>                                                                  <C>            <C>
Proved reserves at December 31, 1992...............................        9,880         60,199
Production.........................................................       (1,204)        (6,914)
                                                                          ------         ------
Proved reserves at December 31, 1993...............................        8,676         53,285
Production.........................................................       (1,142)        (6,778)
                                                                          ------         ------
Proved reserves at December 31, 1994...............................        7,534         46,507
Production.........................................................         (479)        (2,405)
                                                                          ------         ------
Proved reserves at June 12, 1995...................................        7,055         44,102
                                                                          ------         ------
                                                                          ------         ------
Proved developed reserves at June 12, 1995.........................        6,707         38,151
                                                                          ------         ------
                                                                          ------         ------
</TABLE>
 
    STANDARDIZED MEASURE OF DISCOUNTED FUTURE NET CASH FLOWS OF PROVED OIL AND
GAS RESERVES
 
    The  Company has estimated the standardized measure of discounted future net
cash flows  and changes  therein relating  to  proved oil  and gas  reserves  in
accordance  with the standards established by the Financial Accounting Standards
Board through  its Statement  No. 69.  The estimates  of future  cash flows  and
future production and development costs are based on period-end sales prices for
oil  and  gas, estimated  future production  of  proved reserves,  and estimated
future production and  development costs  of proved reserves,  based on  current
costs  and economic  conditions. The  estimated future  net cash  flows are then
discounted at a rate of 10%.
 
    Discounted future net  cash flow estimates  like those shown  below are  not
intended  to  represent  estimates of  the  fair  market value  of  oil  and gas
properties. Estimates  of  fair  market  value  should  also  consider  probable
reserves,  anticipated future  oil and  gas prices,  interest rates,  changes in
development and production  costs and risks  associated with future  production.
Because  of these and other considerations, any estimate of fair market value is
necessarily subjective and imprecise.
 
    The following are the Company's estimated standardized measure of discounted
future net cash flows from proved reserves attributable to the 1995  Acquisition
(in thousands):
 
<TABLE>
<CAPTION>
                                                                        DECEMBER 31,
                                                                   ----------------------
                                                                      1993        1994     JUNE 12, 1995
                                                                   ----------  ----------  -------------
<S>                                                                <C>         <C>         <C>
Future:
  Cash inflows...................................................  $  222,698  $  188,828   $   191,758
  Production costs...............................................    (111,619)    (97,988)      (93,268)
  Development costs..............................................      (4,797)     (4,797)       (4,797)
                                                                   ----------  ----------  -------------
    Net cash flows before income taxes...........................     106,282      86,043        93,693
10% annual discount for estimated timing of cash flows...........     (37,518)    (30,373)      (33,074)
                                                                   ----------  ----------  -------------
Standardized measure of discounted future net cash flows before
 income taxes....................................................  $   68,764  $   55,670   $    60,619
                                                                   ----------  ----------  -------------
                                                                   ----------  ----------  -------------
</TABLE>
 
                                      F-24
<PAGE>
                            COSTILLA ENERGY, L.L.C.
 
                                1995 ACQUISITION
 
 NOTES TO THE STATEMENTS OF REVENUES AND DIRECT OPERATING EXPENSES (CONTINUED)
 
(2) SUPPLEMENTARY FINANCIAL INFORMATION FOR OIL AND GAS PRODUCING ACTIVITIES
(UNAUDITED)
    (CONTINUED)
    The  following are  the sources  of changes  in the  standardized measure of
discounted net cash flows (in thousands):
 
<TABLE>
<CAPTION>
                                                                    YEAR ENDED DECEMBER
                                                                            31,
                                                                   ----------------------  PERIOD ENDED
                                                                      1993        1994     JUNE 12, 1995
                                                                   ----------  ----------  -------------
<S>                                                                <C>         <C>         <C>
Standardized measure, beginning of period........................  $   96,022  $   68,764   $    55,670
Sales, net of production costs...................................     (16,414)    (13,911)       (5,348)
Net change in prices.............................................     (15,892)     (3,910)        8,032
Accretion of discount............................................       9,602       6,876         2,517
Other............................................................      (4,554)     (2,149)         (252)
                                                                   ----------  ----------  -------------
Standardized measure, end of period..............................  $   68,764  $   55,670   $    60,619
                                                                   ----------  ----------  -------------
                                                                   ----------  ----------  -------------
</TABLE>
 
                                      F-25
<PAGE>
                          INDEPENDENT AUDITORS' REPORT
 
The Members
Costilla Energy, L.L.C.:
 
    We have audited the accompanying statements of revenues and direct operating
expenses  of the 1996 Acquisition (see Note  1) for the years ended December 31,
1993, 1994 and 1995.  These statements are the  responsibility of the  Company's
management.  Our responsibility  is to  express an  opinion on  these statements
based on our audits.
 
    We conducted  our  audits in  accordance  with generally  accepted  auditing
standards.  Those standards require that we plan and perform the audit to obtain
reasonable assurance  about  whether  the  statements  of  revenues  and  direct
operating  expenses  are  free  of  material  misstatement.  An  audit  includes
examining, on a test basis, evidence  supporting the amounts and disclosures  in
the  financial  statements.  An  audit also  includes  assessing  the accounting
principles used  and  significant  estimates  made by  management,  as  well  as
evaluating  the  overall  statement  presentation. We  believe  that  our audits
provide a reasonable basis for our opinion.
 
    The accompanying statements of revenues  and direct operating expenses  were
prepared  for the  purpose of  complying with the  rules and  regulations of the
Securities and  Exchange Commission  (for  inclusion in  Forms S-1  of  Costilla
Energy,  Inc. as  described in  Note 1) and  are not  intended to  be a complete
presentation of the 1996 Acquisition interests' revenues and expenses.
 
    In our opinion,  the statements  of revenues and  direct operating  expenses
referred  to above  present fairly, in  all material respects,  the revenues and
direct operating expenses of the 1996  Acquisition for the years ended  December
31,  1993,  1994  and 1995,  in  conformity with  generally  accepted accounting
principles.
 
                                          KPMG PEAT MARWICK LLP
 
Midland, Texas
July 4, 1996
 
                                      F-26
<PAGE>
                            COSTILLA ENERGY, L.L.C.
                                1996 ACQUISITION
              STATEMENTS OF REVENUES AND DIRECT OPERATING EXPENSES
 
                                 (IN THOUSANDS)
 
<TABLE>
<CAPTION>
                                                                                                  (UNAUDITED)
                                                                       YEARS ENDED            THREE-MONTH PERIODS
                                                                      DECEMBER 31,              ENDED MARCH 31,
                                                             -------------------------------  --------------------
                                                               1993       1994       1995       1995       1996
                                                             ---------  ---------  ---------  ---------  ---------
<S>                                                          <C>        <C>        <C>        <C>        <C>
Revenues:
  Oil and condensate.......................................  $  11,467  $  10,170  $  10,564  $   2,659  $   2,799
  Natural gas..............................................     11,294     10,105      8,645      2,031      1,967
  Gas plant................................................         57         57        126         26         23
  Transportation...........................................         39        379        556        139        298
                                                             ---------  ---------  ---------  ---------  ---------
                                                                22,857     20,711     19,891      4,855      5,087
 
Direct operating expenses:
  Lease operating..........................................     10,977      9,053      9,232      1,921      2,179
  Workovers and dry hole costs.............................        675        869      1,002        219        247
  Production taxes.........................................      1,166      1,089        992        246        250
  Gas plant................................................        131        350        598        216        148
  Transportation...........................................         10        394        587        147        122
                                                             ---------  ---------  ---------  ---------  ---------
                                                                12,959     11,755     12,411      2,749      2,946
                                                             ---------  ---------  ---------  ---------  ---------
Revenues in excess of direct operating expenses............  $   9,898  $   8,956  $   7,480  $   2,106  $   2,141
                                                             ---------  ---------  ---------  ---------  ---------
                                                             ---------  ---------  ---------  ---------  ---------
</TABLE>
 
                See the accompanying notes to these statements.
 
                                      F-27
<PAGE>
                            COSTILLA ENERGY, L.L.C.
                                1996 ACQUISITION
       NOTES TO THE STATEMENTS OF REVENUES AND DIRECT OPERATING EXPENSES
 
(1) BASIS OF PRESENTATION
    On June 14, 1996, Costilla Energy, L.L.C. and Costilla Petroleum Corporation
(collectively, the "Company") acquired from  Parker & Parsley Development  L.P.,
Parker  &  Parsley  Producing  L.P.  and Parker  &  Parsley  Gas  Processing Co.
(collectively, "Parker &  Parsley") certain  oil and gas  properties (the  "1996
Acquisition")  for approximately  $42.5 million. The  accompanying statements of
revenues and direct operating expenses for  the 1996 Acquisition do not  include
general and administrative expenses, interest income or expense, a provision for
depreciation,  depletion  and amortization,  or any  provision for  income taxes
since historical expenses of  this nature incurred by  Parker & Parsley are  not
necessarily indicative of the costs to be incurred by the Company.
 
    Historical  financial information reflecting  financial position, results of
operations, and cash flows  of the 1996 Acquisition,  are not presented  because
the  purchase price was assigned to the oil and gas property interests acquired.
Other assets acquired  and liabilities assumed  were not material.  Accordingly,
the  historical statements of revenues and direct operating expenses of the 1996
Acquisition are presented  in lieu  of the financial  statements required  under
Rule 3-05 of Securities and Exchange Commission Regulation S-X.
 
    Revenues  in the  accompanying statements  of revenues  and direct operating
expenses are  recognized on  the  sales method.  Direct operating  expenses  are
recognized on the accrual method.
 
    INTERIM STATEMENTS OF REVENUES AND DIRECT OPERATING EXPENSES
 
    The  interim financial information for the three months ended March 31, 1995
and 1996,  is unaudited.  However, in  the opinion  of management,  the  interim
statements  of revenues and direct operating  expenses include all the necessary
adjustments to fairly present  the results of the  interim periods and all  such
adjustments are of a normal recurring nature. The interim statements of revenues
and  direct operating  expenses should be  read in conjunction  with the audited
statements of  revenues  and  direct  operating expenses  for  the  years  ended
December 31, 1993, 1994 and 1995.
 
(2) SUPPLEMENTARY FINANCIAL INFORMATION FOR OIL AND GAS PRODUCING ACTIVITIES
(UNAUDITED)
 
    ESTIMATED QUANTITIES OF PROVED OIL AND GAS RESERVES
 
    Reserve  information presented below  for the 1996  Acquisition, as of March
31, 1996,  is  based  on  reserve estimates  prepared  by  Williamson  Petroleum
Consultants,  using prices and costs in effect  at that date. Changes in reserve
estimates were  derived  by adjusting  such  quantities and  values  for  actual
production using historical prices and costs.
 
    Proved  reserves are estimated quantities of crude oil and natural gas which
geological and  engineering data  demonstrate with  reasonable certainty  to  be
recoverable  in future years  from known reservoirs  under existing economic and
operating conditions. Proved developed reserves are those which are expected  to
be  recovered  through  existing  wells with  existing  equipment  and operating
methods. Oil  and  gas  reserve  quantity  estimates  are  subject  to  numerous
uncertainties inherent in the estimation of quantities of proved reserves and in
the  projection  of future  rates of  production and  the timing  of development
expenditures. The accuracy  of such estimates  is a function  of the quality  of
available  data and of  engineering and geological  interpretation and judgment.
Results of subsequent drilling, testing  and production may cause either  upward
or  downward revision of previous estimates.  Further, the volumes considered to
be commercially  recoverable  fluctuate with  changes  in prices  and  operating
costs.  The Company emphasizes  that reserve estimates  are inherently imprecise
and that estimates of new discoveries are more imprecise than those of currently
producing oil  and  gas properties.  Accordingly,  these reserve  estimates  are
expected to change as additional information becomes available in the future.
 
                                      F-28
<PAGE>
                            COSTILLA ENERGY, L.L.C.
                                1996 ACQUISITION
 NOTES TO THE STATEMENTS OF REVENUES AND DIRECT OPERATING EXPENSES (CONTINUED)
 
(2) SUPPLEMENTARY FINANCIAL INFORMATION FOR OIL AND GAS PRODUCING ACTIVITIES
(UNAUDITED) (CONTINUED)
    Below  are  the  net  estimated quantities  of  proved  reserves  and proved
developed reserves for the 1996 Acquisition.
 
<TABLE>
<CAPTION>
                                                                                           OIL (MBBLS)   GAS (MMCF)
                                                                                          -------------  -----------
<S>                                                                                       <C>            <C>
Proved reserves at December 31, 1992....................................................        7,211        49,963
Production..............................................................................         (718)       (5,481)
                                                                                                -----    -----------
Proved reserves at December 31, 1993....................................................        6,493        44,482
Production..............................................................................         (685)       (5,217)
                                                                                                -----    -----------
Proved reserves at December 31, 1994....................................................        5,808        39,265
Production..............................................................................         (656)       (4,773)
                                                                                                -----    -----------
Proved reserves at December 31, 1995....................................................        5,152        34,492
Production..............................................................................         (154)         (991)
                                                                                                -----    -----------
Proved reserves at March 31, 1996.......................................................        4,998        33,501
                                                                                                -----    -----------
                                                                                                -----    -----------
Proved developed reserves at March 31, 1996.............................................        4,515        28,961
                                                                                                -----    -----------
                                                                                                -----    -----------
</TABLE>
 
STANDARDIZED MEASURE OF DISCOUNTED FUTURE NET CASH FLOWS OF PROVED OIL AND GAS
RESERVES
 
    The Company has estimated the standardized measure of discounted future  net
cash  flows  and changes  therein relating  to  proved oil  and gas  reserves in
accordance with the standards established by the Financial Accounting  Standards
Board  through its  Statement No.  69. The  estimates of  future cash  flows and
future production and development costs are  based on year-end sales prices  for
oil  and  gas, estimated  future production  of  proved reserves,  and estimated
future production and  development costs  of proved reserves,  based on  current
costs  and economic  conditions. The  estimated future  net cash  flows are then
discounted at a rate of 10%.
 
    Discounted future net  cash flow estimates  like those shown  below are  not
intended  to  represent  estimates of  the  fair  market value  of  oil  and gas
properties. Estimates  of  fair  market  value  should  also  consider  probable
reserves,  anticipated future  oil and  gas prices,  interest rates,  changes in
development and production  costs and risks  associated with future  production.
Because  of these and other considerations, any estimate of fair market value is
necessarily subjective and imprecise.
 
    The following are the Company's estimated standardized measure of discounted
future net cash flows from proved reserves attributable to the 1996  Acquisition
(in thousands):
 
<TABLE>
<CAPTION>
                                                                             DECEMBER 31,
                                                                 ------------------------------------  MARCH 31,
                                                                    1993         1994         1995        1996
                                                                 -----------  -----------  ----------  ----------
<S>                                                              <C>          <C>          <C>         <C>
Future:
  Cash inflows.................................................  $   181,010  $   156,222  $  165,862  $  175,507
  Production costs.............................................     (116,115)    (105,104)    (93,878)    (91,202)
  Development costs............................................       (4,101)      (4,101)     (4,101)     (4,101)
                                                                 -----------  -----------  ----------  ----------
    Net cash flows before income taxes.........................       60,794       47,017      67,883      80,204
10% annual discount for estimated timing of cash flows.........      (22,564)     (17,451)    (25,195)    (29,768)
                                                                 -----------  -----------  ----------  ----------
Standardized measure of discounted future net cash flows before
 income taxes..................................................  $    38,230  $    29,566  $   42,688  $   50,436
                                                                 -----------  -----------  ----------  ----------
                                                                 -----------  -----------  ----------  ----------
</TABLE>
 
                                      F-29
<PAGE>
                            COSTILLA ENERGY, L.L.C.
                                1996 ACQUISITION
 NOTES TO THE STATEMENTS OF REVENUES AND DIRECT OPERATING EXPENSES (CONTINUED)
 
(2) SUPPLEMENTARY FINANCIAL INFORMATION FOR OIL AND GAS PRODUCING ACTIVITIES
(UNAUDITED) (CONTINUED)
    The  following are  the sources  of changes  in the  standardized measure of
discounted net cash flows (in thousands):
 
<TABLE>
<CAPTION>
                                                                                                     THREE-MONTH
                                                                        YEAR ENDED DECEMBER 31,      PERIOD ENDED
                                                                    -------------------------------   MARCH 31,
                                                                      1993       1994       1995         1996
                                                                    ---------  ---------  ---------  ------------
<S>                                                                 <C>        <C>        <C>        <C>
Standardized measure, beginning of year...........................  $  56,372  $  38,230  $  29,566   $   42,688
Sales, net of production costs....................................     (9,943)    (9,264)    (7,983)      (2,090)
Net change in prices..............................................    (11,890)    (2,838)    18,141        9,277
Accretion of discount.............................................      5,637      3,823      2,957        1,067
Other.............................................................     (1,946)      (385)         7         (506)
                                                                    ---------  ---------  ---------  ------------
Standardized measure, end of year.................................  $  38,230  $  29,566  $  42,688   $   50,436
                                                                    ---------  ---------  ---------  ------------
                                                                    ---------  ---------  ---------  ------------
</TABLE>
 
                                      F-30
<PAGE>
                                                                      APPENDIX A
 
                                 July 23, 1996
 
Costilla Energy, Inc.
400 West Illinois, Suite 1000
Midland, Texas 79701
 
Attention  Mr. Michael J. Grella
 
Gentlemen:
 
Subject:    Summary  Letter  (for Inclusion  in a  Prospectus Included  in a
            Registration Statement for  Costilla Energy, Inc.  on Form  S-1)
            Combining   Specific   Data   from   Two   Williamson  Petroleum
            Consultants, Inc. Evaluations (1)  to the Interests of  Costilla
            Petroleum  Corporation  in  Various Properties  and  (2)  to the
            Interests of Parker  & Parsley  Petroleum USA,  Inc. in  Various
            Properties Included in Their First Quarter 1996 Sales Package
            Effective April 1, 1996
            Williamson Project 6.8393
 
    In  accordance  with your  request,  Williamson Petroleum  Consultants, Inc.
(Williamson) has prepared  a summary letter  for inclusion in  a prospectus  for
Costilla  Energy, Inc. (Costilla). The filing of this Prospectus gives effect to
the conversion of Costilla Energy, L.L.C. to Costilla Energy, Inc. This  summary
letter  includes specific  data from two  evaluations the subjects  of which are
described in  Item I.  All values  and  discussion of  proved reserves  and  net
revenues,  data  utilized, assumptions,  and qualifications  are taken  from and
include by reference data from these two evaluations.
 
    Interests in this summary letter represent the April 1, 1996 effective  date
consolidation of the ownership interests of Costilla and the ownership interests
of  Parker & Parsley in various properties  included in their first quarter 1996
sales package  which Costilla  acquired on  June  14, 1996  but which  was  made
effective  as  of  January  1,  1996. The  Costilla  interests  include  all the
interests of  Costilla  Energy, L.L.C.  and  all its  wholly-owned  subsidiaries
including Costilla Petroleum Corporation.
 
I.  THE TWO SUBJECT EVALUATIONS
 
    This  summary  letter  combines  certain proved  oil  and  gas  reserves and
revenues from the following two Williamson evaluations:
 
    (1) Evaluation  of  Oil  and  Gas Reserves  to  the  Interests  of  Costilla
       Petroleum  Corporation in  Various Properties,  Effective April  1, 1996,
       Utilizing Nonescalated Economics,  for Disclosure to  the Securities  and
       Exchange Commission, Williamson Project 6.8393, transmitted July 18, 1996
       (the Costilla report)
 
    (2)  Evaluation of Oil and Gas Reserves to the Interests of Parker & Parsley
       Petroleum USA, Inc. in Various Properties Included in Their First Quarter
       1996 Sales  Package,  Effective  April 1,  1996,  Utilizing  Nonescalated
       Economics,  for  Disclosure to  the  Securities and  Exchange Commission,
       Williamson Project  6.8393, transmitted  July 18,  1996 (the  Acquisition
       report)
 
II.  ESTIMATED SEC RESERVES AND FUTURE NET REVENUES
 
    Projections  of  the  reserves  that are  attributable  to  the consolidated
interests in this summary letter were based on economic parameters and operating
conditions considered applicable  as of April  1, 1996 and  are pursuant to  the
requirements of the Securities and Exchange Commission (SEC).
 
    In  accordance with  instructions from  Costilla, Williamson  utilized lease
operating expenses for the Costilla-operated  properties in the Costilla  report
that  excluded COPAS overhead and internal indirect overhead which are billed to
outside working interest owners. The exclusion  of these costs for the  operated
properties  results in the calculation of a  lower economic limit and causes the
economic lifetime to be
 
                                      A-1
<PAGE>
Costilla Energy, Inc.
Mr. Michael J. Grella
July 23, 1996
Page 2
extended. Williamson has not quantified the incremental reserves resulting  from
this  procedure. COPAS overhead  was excluded from  the lease operating expenses
for the Parker & Parsley-operated properties in the Acquisition report.
 
    The present values of the estimated future net revenues from proved reserves
were calculated  using  a discount  rate  of 10.00  percent  per year  and  were
computed  in accordance  with the financial  reporting requirements  of the SEC.
Following is a summary of the results of the two evaluations effective April  1,
1996:
 
<TABLE>
<CAPTION>
                                                   PROVED           PROVED
                                                  DEVELOPED        DEVELOPED           PROVED           TOTAL
                                                  PRODUCING      NONPRODUCING       UNDEVELOPED        PROVED
                                                -------------  -----------------  ----------------  -------------
<S>                                             <C>            <C>                <C>               <C>
Net Reserves to the Evaluated Interests:
  Oil/Condensate, BBL.........................     13,122,088          429,450          2,924,589      16,476,127
  Gas, MCF....................................     76,439,217        7,929,591         28,551,497     112,920,305
Future Net Revenue, $:
  Undiscounted................................    212,071,507       18,097,949         66,832,632     297,002,088
  Discounted Per Annum at 10.00 Percent.......    135,185,097        9,530,285         34,811,523     179,526,905
</TABLE>
 
- ------------------------
Note: The values presented in this table are taken from evaluations described in
      Item  I and include by reference all data, qualifications, and assumptions
      from these  evaluations.  Realization of  these  values is  contingent  on
      achieving successful results from the various schedules and assumptions in
      these  evaluations. The  available engineering  data and  the completeness
      and/or quality of data utilized in evaluating the properties are  detailed
      in  the specific evaluation. Review of any additionally available data may
      necessitate revision to these  interpretations and assumptions and  impact
      these values.
 
III.  DEFINITIONS OF SEC RESERVES (1)
 
    The  estimated  reserves presented  in this  summary  letter are  net proved
reserves, including proved developed  producing, proved developed  nonproducing,
and  proved  undeveloped  reserves, and  were  computed in  accordance  with the
financial reporting requirements of the SEC. In preparing these evaluations,  no
attempt has been made to quantify the element of uncertainty associated with any
category.  Reserves were assigned to each category as warranted. The definitions
of oil and gas reserves pursuant to the requirements of the Securities  Exchange
Act are:
 
PROVED RESERVES (2)
 
    Proved  reserves are the estimated quantities of crude oil, natural gas, and
natural gas  liquids  which geological  and  engineering data  demonstrate  with
reasonable  certainty to  be recoverable in  future years  from known reservoirs
under the economic  criteria employed and  existing operating conditions,  i.e.,
prices  and costs as of the date the  estimate is made. Prices and costs include
consideration of changes provided  only by contractual  arrangements but not  on
escalations based upon an estimate of future conditions.
 
A.  Reservoirs are considered  proved if economic  producibility is supported by
    either actual  production  or  conclusive  formation test.  The  area  of  a
    reservoir considered proved includes:
 
    1.    that portion  delineated  by drilling  and  defined by  gas-oil and/or
       oil-water contacts, if any; and
 
- ------------------------
(1) For  evaluations prepared  for  disclosure to  the Securities  and  Exchange
    Commission,  see SEC ACCOUNTING RULES. Commerce Clearing House, Inc. October
    1981, Paragraph 290, Regulation 210.4-10, p. 329.
 
(2) Any variations to these definitions will be clearly stated in the report.
 
                                      A-2
<PAGE>
Costilla Energy, Inc.
Mr. Michael J. Grella
July 23, 1996
Page 3
 
    2.  the  immediately adjoining portions  not yet drilled,  but which can  be
       reasonably  judged as economically  productive on the  basis of available
       geological and engineering data. In  the absence of information on  fluid
       contacts, the lowest known structural occurrence of hydrocarbons controls
       the lower proved limit of the reservoir.
 
B.   Reserves which can be produced economically through application of improved
    recovery techniques (such as fluid  injection) are included in the  "proved"
    classification  when successful testing by a pilot project, or the operation
    of  an  installed  program  in  the  reservoir,  provides  support  for  the
    engineering analysis on which the project or program was based.
 
C.  Estimates of proved reserves do not include the following:
 
    1.   oil that may  become available from known  reservoirs but is classified
       separately as "indicated additional reserves;"
 
    2.  crude oil, natural gas, and  natural gas liquids, the recovery of  which
       is  subject to  reasonable doubt  because of  uncertainty as  to geology,
       reservoir characteristics, or economic factors;
 
    3.  crude  oil, natural  gas, and  natural gas  liquids, that  may occur  in
       undrilled prospects; and
 
    4.   crude oil, natural gas, and  natural gas liquids, that may be recovered
       from oil shales, coal (3), gilsonite and other such sources.
 
PROVED DEVELOPED RESERVES (4)
 
    Proved developed reserves are reserves that can be expected to be  recovered
through existing wells with existing equipment and operating methods. Additional
oil  and gas expected to be obtained  through the application of fluid injection
or other improved recovery techniques  for supplementing the natural forces  and
mechanisms of primary recovery should be included as "proved developed reserves"
only  after testing by  a pilot project  or after the  operation of an installed
program has confirmed through production  response that increased recovery  will
be achieved.
 
PROVED UNDEVELOPED RESERVES
 
    Proved  undeveloped reserves are reserves that  are expected to be recovered
from new wells on undrilled acreage,  or from existing wells where a  relatively
major  expenditure is required  for recompletion. Reserves  on undrilled acreage
shall be limited to  those drilling units offsetting  productive units that  are
reasonably  certain  of  production  when  drilled.  Proved  reserves  for other
undrilled units can be claimed only where it can be demonstrated with  certainty
that  there is continuity of production  from the existing productive formation.
Under no  circumstances  should estimates  for  proved undeveloped  reserves  be
attributable to any acreage for which an application of fluid injection or other
improved  recovery technique is  contemplated, unless such  techniques have been
proved effective by actual tests in the area and in the same reservoir.
 
- ------------------------
(3) According to Staff Accounting Bulletin 85, excluding certain coalbed methane
    gas.
 
(4) Williamson Petroleum Consultants,  Inc. separates proved developed  reserves
    into  proved developed producing and proved developed nonproducing reserves.
    This is  to identify  proved developed  producing reserves  as those  to  be
    recovered  from  actively  producing  wells;  proved  developed nonproducing
    reserves as those  to be  recovered from  wells or  intervals within  wells,
    which   are  completed  but  shut  in   waiting  on  equipment  or  pipeline
    connections, or wells where a  relatively minor expenditure is required  for
    recompletion to another zone.
 
                                      A-3
<PAGE>
Costilla Energy, Inc.
Mr. Michael J. Grella
July 23, 1996
Page 4
 
IV.  DISCUSSION OF SEC RESERVES
 
A. THE COSTILLA REPORT
 
    A  total of 1,014  properties in 294  fields were evaluated  in the Costilla
    report. Nineteen individual properties had  values greater than 1.0  percent
    of the total future net revenue discounted at 10.00 percent per annum (DFNR)
    and  in aggregate represent 34.5 percent of the DFNR in the Costilla report.
    The most valued property, the T.B. Pruett  Gas Unit No. 3, Soda Lake  field,
    Ward  County, Texas, had a  value equal to 4.5 percent  of the total DFNR in
    the Costilla report. The top  eight major-value fields are Talbot  (Canyon),
    Howard  County, Texas; Spraberry (Trend Area), Various Counties, Texas; Soda
    Lake (Fusselman), Ward  County, Texas;  South Buffalo  Ridge, Crane  County,
    Texas;  Wattenberg,  Weld County,  Colorado;  East Goldsmith,  Ector County,
    Texas; Raymond,  Sheridan County,  Montana; and  South West  Speaks,  Lavaca
    County,  Texas. These fields contain ten of  the 19 top value properties and
    represent, in aggregate,  41.0 percent  of the  total DFNR  in the  Costilla
    report. The remaining 286 fields represent 59.0 percent with no field having
    more  than 2.9 percent of  the DFNR in the  Costilla report. A more detailed
    property review is included in the Costilla report.
 
    Area oil prices were provided by Costilla  to be used at the effective  date
    with  the written assurance that the use  of these area prices is reasonable
    on an aggregate basis  and would not materially  affect the income from  any
    major-value  property. These  area prices  were calculated  by adjusting the
    West Texas Intermediate oil April 1, 1996 posted price of $20.75 per barrel.
    The oil  price adjustments  for  each area  are the  calculated  differences
    between  the actual price received during 1995 and the posted price for West
    Texas Intermediate oil during  that same period.  After the effective  date,
    prices  were held constant  for the life  of the properties.  No attempt has
    been made to account for oil  price fluctuations which have occurred in  the
    market subsequent to the effective date of this report.
 
    Gas prices were provided by Costilla to be used at the effective date. These
    prices  were based on the April 1996 spot price of $1.75 per million British
    thermal units  (MMBTU) at  the Waha,  Texas receipt  point. This  price  was
    adjusted  with  an  area  price  adjustment  which  was  calculated  as  the
    difference between the actual price received during 1995 and the stop price.
    The resultant price was further adjusted for the BTU content of the gas  for
    each  well. If the BTU  content was unknown, it was  assumed to be one MMBTU
    per MCF of gas. After the effective date, prices were held constant for  the
    life  of the properties unless Costilla indicated that changes were provided
    for by contract. All gas prices were applied to projected wellhead volumes.
 
    It should  be  emphasized  that with  the  current  economic  uncertainties,
    fluctuation in market conditions could significantly change the economics of
    the properties included in this report.
 
    Operating expenses were provided by Costilla and represented, when possible,
    the  latest available 12-month  average of all  recurring expenses excluding
    COPAS and internal indirect overhead costs which are billable to the working
    interest owners.  These expenses  included,  but were  not limited  to,  all
    direct  operating expenses, field  overhead costs, and  any ad valorem taxes
    not deducted  separately. Expenses  for  workovers, well  stimulations,  and
    other  maintenance were not  included in the  operating expenses unless such
    work was expected on a recurring  basis. Judgments for the exclusion of  the
    nonrecurring expenses were made by Costilla. In accordance with instructions
    from  Costilla, Williamson has excluded COPAS overhead and internal indirect
    overhead which are billed  to the outside working  interest owners from  the
    operating  expenses for Costilla-operated properties. The exclusion of these
    costs for operated properties results in the calculation of a lower economic
    limit and causes the  economic lifetime to be  extended. Williamson has  not
    calculated  the reserves that have been added as a result of this procedure.
    For new and  developing properties  where data  were unavailable,  operating
    expenses  were estimated by Costilla. Operating costs were held constant for
    the life of the properties.
 
                                      A-4
<PAGE>
Costilla Energy, Inc.
Mr. Michael J. Grella
July 23, 1996
Page 5
 
    State production  taxes  have  been  deducted  at  the  published  rates  as
    appropriate.  For  operated  properties,  average  county  ad  valorem taxes
    provided by Costilla were  deducted for those  properties located in  states
    for  which the  data were  available. Any  ad valorem  taxes for nonoperated
    properties or for properties in other states were assumed to be included  in
    the operating expenses.
 
    All  capital costs  for drilling  and completion  of wells  and nonrecurring
    workover or operating costs  have been deducted  as applicable. These  costs
    were  provided  by Costilla.  No adjustments  were made  to account  for the
    potential effect of inflation on these costs.
 
    Neither salvage values nor abandonment costs were provided by Costilla to be
    included in this evaluation.
 
B.  THE ACQUISITION REPORT
 
    A total of 1,091 properties in 135 fields were evaluated in the  Acquisition
    report.  Eighteen individual properties had  values greater than 1.0 percent
    of the total DFNR and in aggregate represent 35.5 percent of the DFNR in the
    Acquisition report.  The  most valued  property,  the H.W.  Glasscock  Unit,
    Howard-Glasscock  field, Glasscock County,  Texas, has a  projected value of
    5.7 percent  of the  total DFNR  in the  Acquisition report.  The top  eight
    major-value  fields  are  World,  Crockett  County,  Texas;  Dimmitt, Loving
    County,  Texas;  Panna  Maria,  Karnes  County,  Texas;  Giddings,   Various
    Counties,  Texas; Caldwell, Burleson County,  Texas; Coletto Creek, Victoria
    County, Texas;  Sawyer,  Sutton County,  Texas;  and Jameson,  Coke  County,
    Texas. These fields contain 11 of the 18 top value properties and represent,
    in  aggregate, 51.9 percent of the total DFNR in the Acquisition report. The
    remaining fields represent 48.1 percent with  no field having more than  2.9
    percent  of the  DFNR in  the Acquisition  report. A  more detailed property
    review is included in the Acquisition report.
 
    Area oil prices were provided by Costilla and Parker & Parsley to be used at
    the effective date  with the written  assurance that the  use of these  area
    prices  is reasonable on an aggregate  basis and would not materially affect
    the income from any major-value property. These area prices were  calculated
    by  adjusting the West Texas Intermediate oil  April 1, 1996 posted price of
    $20.75 per  barrel. The  oil price  adjustments as  calculated by  Parker  &
    Parsley  for each  area are  the calculated  differences between  the actual
    price received during 1995 and the posted price for West Texas  Intermediate
    oil  during that  same period.  After the  effective date,  prices were held
    constant for the life of the properties. No attempt has been made to account
    for oil price fluctuations which have  occurred in the market subsequent  to
    the effective date of this report.
 
    Gas  prices were provided by Costilla and Parker & Parsley to be used at the
    effective date. These  prices were  based on the  April 1996  spot price  of
    $1.75  per million British thermal units  (MMBTU) at the Waha, Texas receipt
    point. This  price was  adjusted with  an area  price adjustment  which  was
    calculated  as the difference between the  actual price received during 1995
    and the stop  price. The resultant  price was further  adjusted for the  BTU
    content  of the gas  for each well. If  the BTU content  was unknown, it was
    assumed to be one  MMBTU per MCF  of gas. After  the effective date,  prices
    were  held constant for the life of the properties unless Costilla indicated
    that changes were provided for by  contract. All gas prices were applied  to
    projected wellhead volumes.
 
    It  should  be  emphasized  that with  the  current  economic uncertainties,
    fluctuation in market conditions could significantly change the economics of
    the properties included in this report.
 
    Operating expenses  were  provided by  Costilla  and Parker  &  Parsley  and
    represented,  when possible,  the latest  available 12-month  average of all
    recurring expenses  excluding COPAS  and  internal indirect  overhead  costs
    which  are billable to the working interest owners. These expenses included,
    but were  not limited  to,  all direct  operating expenses,  field  overhead
    costs, and any ad valorem taxes not deducted
 
                                      A-5
<PAGE>
Costilla Energy, Inc.
Mr. Michael J. Grella
July 23, 1996
Page 6
    separately. Expenses for workovers, well stimulations, and other maintenance
    were not included in the operating expenses unless such work was expected on
    a  recurring basis. Judgments for the exclusion of the nonrecurring expenses
    were made by Costilla or Parker  & Parsley. In accordance with  instructions
    from Costilla, Williamson has excluded COPAS overhead which is billed to the
    outside  working interest  owners from the  operating expenses  for Parker &
    Parsley-operated properties.  The  exclusion  of these  costs  for  operated
    properties  results in the calculation of  a lower economic limit and causes
    the economic  lifetime to  be extended.  Williamson has  not calculated  the
    reserves  that have been  added as a  result of this  procedure. For new and
    developing properties where data  were unavailable, operating expenses  were
    estimated  by  Costilla  or  Parker &  Parsley.  Operating  costs  were held
    constant for the life of the properties.
 
    State production  taxes  have  been  deducted  at  the  published  rates  as
    appropriate.  For  operated  properties,  average  county  ad  valorem taxes
    provided by Costilla were  deducted for those  properties located in  states
    for  which the  data were  available. Any  ad valorem  taxes for nonoperated
    properties or for properties in other states were assumed to be included  in
    the operating expenses.
 
    All  capital costs  for drilling  and completion  of wells  and nonrecurring
    workover or operating costs  have been deducted  as applicable. These  costs
    were  provided by Costilla or Parker &  Parsley. No adjustments were made to
    account for the potential effect of inflation on these costs.
 
    Neither salvage values nor abandonment costs were provided by Costilla to be
    included in this evaluation.
 
V.  GENERAL EVALUATION CONSIDERATIONS PERTAINING TO THE COSTILLA AND ACQUISITION
    REPORTS
 
    The individual projections prepared to  produce this summary letter  include
data that describe the production forecasts and associated evaluation parameters
such  as interests, taxes, product prices, operating costs, investments, salvage
values, abandonment costs, and net profit interests, as applicable.
 
    Net income to the evaluated interests  is the future net revenue payable  to
others,  taxes,  operating  expenses, investments,  salvage  values, abandonment
costs, and net profit interests, as applicable. The future net revenue is before
federal income tax and  excludes consideration of  any encumbrances against  the
properties if such exist.
 
    No  opinion is expressed  by Williamson as  to the fair  market value of the
evaluated properties.
 
    The future  net revenues  presented in  this summary  letter were  based  on
projections  of  oil  and gas  production.  It  was assumed  there  would  be no
significant delay between the date of oil and gas production and the receipt  of
the associated revenue for this production.
 
    This  summary  letter  includes  only those  costs  and  revenues  which are
considered by  Costilla to  be directly  attributable to  individual leases  and
areas.  There  could  exist  other  revenues,  overhead  costs,  or  other costs
associated with Costilla  which are not  included in this  summary letter.  Such
additional costs and revenues are outside the scope of this summary letter. This
summary  letter is not a financial statement for Costilla and should not be used
as the sole basis for any transaction concerning Costilla, Parker & Parsley,  or
the evaluated properties.
 
    The  reserves projections in this summary letter are based on the use of the
available data and accepted industry engineering methods. Future changes in  any
operational   or  economic  parameters  or  production  characteristics  of  the
evaluated properties  could  increase  or decrease  their  reserves.  Unforeseen
changes  in market demand or allowables set by various regulatory agencies could
also cause actual production  rates to vary from  those projected. The dates  of
first production for nonproducing properties were based on
 
                                      A-6
<PAGE>
Costilla Energy, Inc.
Mr. Michael J. Grella
July 23, 1996
Page 7
estimates  by Costilla or  Williamson and the  actual dates may  vary from those
estimated.  Williamson  reserves  the  right  to  alter  any  of  the   reserves
projections  and the associated economics included in this summary letter in any
future evaluation based on additional data that may be acquired.
 
    All data utilized in the preparation of this summary letter with respect  to
interests, reversionary status, oil and gas prices, gas categories, gas contract
terms,  operating expenses, investments, salvage  values, abandonment costs, net
profit  interests,  well  information  and  current  operating  conditions,   as
applicable, were provided by Costilla, Parker & Parsley, and the operators. Data
obtained  after the effective date of the  report but prior to the completion of
the report were used only if such  data were applied consistently. If such  data
were  used, the reserves category assignments reflect the status of the wells as
of the effective date. In the Costilla report, daily production data after April
1, 1996 were utilized  for new wells  in the South  Buffalo Ridge, Concho  Bluff
(Queen),  East  Goldsmith (Queen),  King  Mountain (Penn),  and  Talbot (Canyon)
fields to  assist in  determining  initial producing  and decline  rates.  Daily
production  since the effective date was also used  for the Pyote Gas Unit 5 No.
1A, Block 16  (Devonian) field, Ward  County, Texas to  establish the  producing
rate  after the well was affected by gas  plant problems and for the State 16-05
well in the  Raymond field, Sheridan  County, Montana to  establish the  initial
rate of production subsequent to the installation of a downhole pump. Production
data  generally through December  1995 or January 1996  provided by Costilla for
the properties in  the Costilla  report and  through November  or December  1995
provided  by Parker & Parsley for the  properties in the Acquisition report were
utilized. All data  have been  reviewed for reasonableness  and, unless  obvious
errors  were detected,  have been accepted  as correct. It  should be emphasized
that revisions to  the projections of  reserves and economics  included in  this
summary  letter may be required if the provided data are revised for any reason.
No inspection of the properties was made  as this was not considered within  the
scope  of  these  projects.  No  investigation  was  made  of  any environmental
liabilities that  might apply  to the  evaluated properties,  and no  costs  are
included for any possible related expenses.
 
    Unless  specifically  identified  and  documented by  Costilla  or  Parker &
Parsley as having curtailment problems, gas production trends have been  assumed
to  be a function of well productivity  and not of market conditions. The effect
of "take or pay" clauses in gas contracts was not considered.
 
    Oil reserves  are expressed  in  United States  (U.S.)  barrels of  42  U.S.
gallons.  Gas  volumes are  expressed in  thousands  of cubic  feet (MCF)  at 60
degrees Fahrenheit and at the legal pressure base that prevails in the state  in
which the reserves are located. No adjustment of the individual gas volumes to a
common pressure base has been made.
 
    Costilla  represented  to  Williamson  that it  has,  or  can  generate, the
financial and operational capabilities to accomplish those projects evaluated by
Williamson which require capital expenditures.
 
    The estimates of reserves contained  in this summary letter were  determined
by  accepted industry methods and in accordance  with the definitions of oil and
gas reserves set forth  above. Methods utilized in  this summary letter  include
extrapolation  of historical production trends, material balance determinations,
analogy to similar properties, and volumetric calculations.
 
    Where sufficient production history and other data were available,  reserves
for   producing  properties  were  determined  by  extrapolation  of  historical
production trends or through the use of material balance determinations. Analogy
to similar  properties or  volumetric calculations  were used  for  nonproducing
properties  and those  producing properties  which lacked  sufficient production
history and other  data to  yield a  definitive estimate  of reserves.  Reserves
projections  based on analogy are subject to change due to subsequent changes in
the analogous properties or subsequent production from the evaluated properties.
Volumetric calculations are often  based upon limited  log and/or core  analysis
data and incomplete reservoir
 
                                      A-7
<PAGE>
Costilla Energy, Inc.
Mr. Michael J. Grella
July 23, 1996
Page 8
fluid  and  formation rock  data. Since  these limited  data must  frequently be
extrapolated over an  assumed drainage area,  subsequent production  performance
trends  or  material balance  calculations may  cause  the need  for significant
revisions to the estimates of reserves.
 
    It should  be  emphasized  that with  the  current  economic  uncertainties,
fluctuation  in market  conditions could  significantly change  the economics in
this summary letter.
 
VII.  DECLARATION OF INDEPENDENT STATUS AND CONSENT
 
    We understand  that our  estimates  are to  be  included in  a  Registration
Statement  on Form S-1 (the Registration Statement) to be filed with the SEC and
in the  Prospectus as  included in  such Registration  Statement which  will  be
registered under the Securities Act of 1933, as amended.
 
    Williamson  is an independent consulting firm and does not own any interests
in the oil and gas properties covered by this summary letter. Roy C. Williamson,
Jr., Chief Executive Officer, owns a  2.5 percent working interest in six  wells
in  the Outlook  field, Sheridan  County, Montana, which  have a  total value of
$138,912 to  the interests  of Costilla.  No employee,  officer or  director  of
Williamson  is an employee, officer or director of Costilla or Parker & Parsley.
Neither the  employment  of  nor  the compensation  received  by  Williamson  is
contingent  upon the values  assigned to the  oil and gas  properties covered by
this summary letter.
 
    We consent  to the  inclusion of  this summary  letter in  the  Registration
Statement,  the inclusion in  the Registration Statement  of data extracted from
this summary  letter  and to  all  references to  our  firm in  the  Prospectus,
including any references to our firm as Experts.
 
                                    Yours very truly,
 
                                    WILLIAMSON PETROLEUM CONSULTANTS, INC.
 
                                      A-8
<PAGE>
- -------------------------------------------------
                               -------------------------------------------------
- -------------------------------------------------
                               -------------------------------------------------
 
NO  DEALER,  SALESMAN  OR ANY  OTHER  PERSON  HAS BEEN  AUTHORIZED  TO  GIVE ANY
INFORMATION OR TO MAKE  ANY REPRESENTATIONS OTHER THAN  THOSE CONTAINED IN  THIS
PROSPECTUS IN CONNECTION WITH THE OFFER MADE BY THIS PROSPECTUS AND, IF GIVEN OR
MADE, SUCH INFORMATION OR REPRESENTATIONS MUST NOT BE RELIED UPON AS HAVING BEEN
AUTHORIZED  BY THE COMPANY OR ANY OF  THE UNDERWRITERS. THIS PROSPECTUS DOES NOT
CONSTITUTE AN OFFER TO SELL OR THE SOLICITATION OF ANY OFFER TO BUY ANY SECURITY
OTHER THAN THE SHARES OF  COMMON STOCK OFFERED BY  THIS PROSPECTUS, NOR DOES  IT
CONSTITUTE  AN OFFER TO SELL OR A SOLICITATION OF ANY OFFER TO BUY THE SHARES OF
COMMON STOCK BY ANYONE IN ANY  JURISDICTION IN WHICH SUCH OFFER OR  SOLICITATION
IS  NOT AUTHORIZED, OR IN WHICH THE  PERSON MAKING SUCH OFFER OR SOLICITATION IS
NOT QUALIFIED TO DO  SO, OR TO ANY  PERSON TO WHOM IT  IS UNLAWFUL TO MAKE  SUCH
OFFER OR SOLICITATION. NEITHER THE DELIVERY OF THIS PROSPECTUS NOR ANY SALE MADE
HEREUNDER  SHALL,  UNDER  ANY  CIRCUMSTANCES, CREATE  ANY  IMPLICATION  THAT THE
INFORMATION CONTAINED HEREIN IS  CORRECT AS OF ANY  TIME SUBSEQUENT TO THE  DATE
HEREOF.
 
UNTIL               , 1996, ALL DEALERS EFFECTING TRANSACTIONS IN THE REGISTERED
SECURITIES,  WHETHER OR NOT PARTICIPATING IN  THIS DISTRIBUTION, MAY BE REQUIRED
TO DELIVER A PROSPECTUS.  THIS IS IN  ADDITION TO THE  OBLIGATION OF DEALERS  TO
DELIVER  A  PROSPECTUS WHEN  ACTING AS  UNDERWRITERS AND  WITH RESPECT  TO THEIR
UNSOLD ALLOTMENTS OR SUBSCRIPTIONS.
 
                                ----------------
 
                               TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                                                               PAGE
                                                               ----
<S>                                                     <C>
Prospectus Summary....................................           3
Risk Factors..........................................           9
The Company...........................................          14
Notes Offering........................................          14
Use of Proceeds.......................................          15
Dividend Policy.......................................          15
Dilution..............................................          16
Capitalization........................................          17
Pro Forma Condensed Financial Statements..............          18
Selected Financial Information........................          26
Management's Discussion and Analysis of Financial
 Condition and Results of Operations..................          27
Business and Properties...............................          32
Management............................................          44
Security Ownership of Certain Beneficial Owners and
 Management...........................................          47
Executive Compensation and Other Information..........          48
Certain Transactions..................................          50
Description of Certain Indebtedness...................          51
Description of Capital Stock..........................          53
Shares Eligible for Future Sale.......................          56
Underwriting..........................................          57
Legal Matters.........................................          58
Experts...............................................          58
Available Information.................................          58
Glossary..............................................          60
Index to Financial Statements.........................         F-1
Summary Reserve Report................................         A-1
</TABLE>
 
                                4,000,000 Shares
 
                             COSTILLA ENERGY, INC.
 
                                  Common Stock
 
                                 -------------
 
                                   PROSPECTUS
 
                                 -------------
 
                       PRUDENTIAL SECURITIES INCORPORATED
 
                         RAUSCHER PIERCE REFSNES, INC.
 
                                August   , 1996
 
- -------------------------------------------------
                               -------------------------------------------------
- -------------------------------------------------
                               -------------------------------------------------
<PAGE>
                                    PART II
 
                     INFORMATION NOT REQUIRED IN PROSPECTUS
 
ITEM 13.  OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION.
 
<TABLE>
<S>                                                                  <C>
SEC registration fee...............................................  $  20,690
NASD filing fee....................................................      7,860
Nasdaq listing fee.................................................      *
Blue Sky fees and expenses.........................................     15,000
Accounting fees and expenses.......................................      *
Engineering fees and expenses......................................      *
Transfer Agent fees and expenses...................................      *
Legal fees and expenses............................................      *
Printing and mailing expenses......................................      *
Miscellaneous......................................................
                                                                     ---------
      TOTAL........................................................
                                                                     ---------
                                                                     ---------
</TABLE>
 
- ------------------------
* To be provided by amendment.
 
ITEM 14.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.
 
    Section  145 of the General Corporation Law of the State of Delaware permits
a corporation to indemnify certain persons, including officers and directors and
former officers  and  directors,  and  to purchase  insurance  with  respect  to
liability  arising out  of their capacity  or status as  officers and directors.
Such law provides  further that the  indemnification permitted thereunder  shall
not  be deemed exclusive of any other rights to which officers and directors may
be entitled under the corporation's bylaws, any agreement or otherwise.  Article
IX  of  the  Company's Certificate  of  Incorporation, included  in  Exhibit 3.1
hereto, and Article VI of the Company's Bylaws, included in Exhibit 3.2  hereto,
provide, in general, that the Company shall indemnify its directors and officers
under the circumstances defined in Section 145 of the General Corporation Law of
the  State of Delaware and gives authority  to the Company to purchase insurance
with respect to  such indemnification.  The Company may  in the  future seek  to
obtain  insurance providing for indemnification of officers and directors of the
Company and certain other persons  against liabilities and expenses incurred  by
any of them in certain stated proceedings and under certain stated conditions.
 
    In  addition, Section 102(b)(7) of the  General Corporation Law of the State
of Delaware  permits a  corporation  to limit  the  liability of  its  directors
subject  to certain exceptions. In accordance with Section 102(b)(7), Article VI
of the Company's Certificate of  Incorporation, included in Exhibit 3.1  hereto,
provides, in general, that no director of the Company shall be personally liable
for  (i) any  breach of  the directors' duty  of loyalty  to the  Company or its
stockholders, (ii)  acts  or  omissions  not in  good  faith  or  which  involve
intentional misconduct or a knowing violation of law, (iii) unlawful payments of
dividends  or unlawful stock  repurchases or redemptions  as provided in Section
174 of  the  General Corporation  Law  of the  State  of Delaware  or  (iv)  any
transaction from which the director derived an improper personal benefit.
 
    The  Underwriting Agreement provides for indemnification by the Underwriters
of the Registrant,  its directors  and officers, and  by the  Registrant of  the
Underwriters,  for certain liabilities, including  liabilities arising under the
Securities Act of 1933 (the "Securities Act").
 
ITEM 15.  RECENT SALES OF UNREGISTERED SECURITIES.
 
    Prior to the consummation of the Offerings, the Company issued an  aggregate
of  300 shares of Common  Stock to Messrs. Liedtke,  Grella and Musselman in its
initial capitalization,  which  shares were  cancelled  in connection  with  the
Corporate  Reorganization, and an aggregate of  6,000,000 shares of Common Stock
to the four  members of  the LLC  in the merger  of the  LLC with  and into  the
Company.  Such shares were  not registered under the  Securities Act in reliance
upon the exemption from registration provided by Section 4(2) thereof.
 
                                      II-1
<PAGE>
ITEM 16.  EXHIBITS AND FINANCIAL STATEMENT SCHEDULES.
 
    (a) Exhibits
 
<TABLE>
<CAPTION>
 EXHIBIT
  NUMBER                                    DESCRIPTION OF EXHIBIT
- ----------  --------------------------------------------------------------------------------------
<C>         <S>
     *1.1   Form of Underwriting Agreement
   ***3.1   Certificate of Incorporation of the Company
   ***3.2   Bylaws of the Company
   ***4.1   Form of Notes or Global Certificate (included as Exhibit A to the form of Indenture
            filed as Exhibit Number 4.2 to the Registration Statement on Form S-1, File No.
            333-     , filed with respect to the Notes)
   ***4.2   Form of Indenture
    **4.3   Form of Stock Certificate
    **5.1   Opinion of Cotton, Bledsoe, Tighe & Dawson, a Professional Corporation
    **6.1   Purchase and Sale Agreement dated April 3, 1995 by and between Parker & Parsley
            Development L.P. and Parker & Parsley Producing L.P. and Parker & Parsley Gas
            Processing Co. as Seller and Costilla Petroleum Corporation and Costilla Energy,
            L.L.C. as Purchaser
    **6.2   Purchase and Sale Agreement dated March 8, 1996 by and between Parker & Parsley
            Development L.P. and Parker & Parsley Producing L.P. and Parker & Parsley Gas
            Processing Co. as Seller and Costilla Petroleum Corporation and Costilla Energy,
            L.L.C. as Purchaser
   **10.1   Form of Credit Agreement to be entered into contemporaneously with the closing of the
            Offerings between the Company as Borrower and                      as Lender.
  ***10.2   Lease Agreement dated January 12, 1996 between Independence Plaza, Ltd. and Costilla
            Energy, L.L.C.
  ***10.3   Concession Agreement dated July 6, 1995 between the Government of the Republic of
            Moldova and the Resource Development Company, Limited.
  ***10.4   Purchase and Joint Exploration Agreement dated February 21, 1996 between the Company
            and Resources Development Limited, L.L.C. (DE).
   **10.5   Consolidation Agreement to be effective contemporaneously with closing of the
            Offerings to consummate the Corporate Reorganization.
   **10.6   1996 Stock Option Plan.
   **10.7   Outside Directors Stock Option Plan.
  ***10.8   Employment Agreement between the Company and Bobby W. Page effective June 30, 1996.
   **10.9   Employment Agreement between the Company and Cadell S. Liedtke to be effective
            contemporaneously with the closing of the Offerings.
   **10.10  Employment Agreement between the Company and Michael J. Grella to be effective
            contemporaneously with the closing of the Offerings.
   **10.11  Employment Agreement between the Company and Henry G. Musselman to be effective
            contemporaneously with the closing of the Offerings.
  ***10.12  Exchange Agreement dated January 5, 1995 between Costilla Petroleum Corporation and
            Koch Oil Company.
  ***10.13  Agreement dated January 2, 1996 between Costilla Petroleum Corporation and Frontier
            Oil and Refining Company.
</TABLE>
 
                                      II-2
<PAGE>
<TABLE>
<CAPTION>
 EXHIBIT
  NUMBER                                    DESCRIPTION OF EXHIBIT
- ----------  --------------------------------------------------------------------------------------
<C>         <S>
  ***12.1   Computation of Ratio of EBITDA to Interest Expense
  ***12.2   Computation of Ratio of Earnings to Fixed Charges
  ***21.1   Subsidiaries of the Registrant
    *23.1   Consent of KPMG Peat Marwick LLP
    *23.2   Consent of Williamson Petroleum Consultants, Inc.
    *23.3   Consent of Elms, Faris & Co., P.C.
   **23.4   Consent of Cotton, Bledsoe, Tighe & Dawson, a Professional Corporation (such consent
            is included in the opinion filed as Exhibit 5.1 to this Registration Statement)
    *24.1   Power of Attorney
    *24.2   Certified copy of resolution of Board of Directors of Costilla Energy, Inc.
            authorizing signature pursuant to Power of Attorney
    *27.1   Financial Data Schedule
</TABLE>
 
- ------------------------
*   Filed herewith
**  To be filed by amendment
*** Incorporated by reference to Registration Statement on Form S-1, File No.
    333-      , filed with respect to the Notes
 
    (b) Financial Statement Schedules.
 
ITEM 17.  UNDERTAKINGS
 
    Insofar as indemnification for liabilities arising under the Securities  Act
may  be  permitted  to  directors,  officers  and  controlling  persons  of  the
Registrant pursuant  to  the  provisions  described  under  Item  14  above,  or
otherwise, the Registrant has been advised that in the opinion of the Securities
and  Exchange  Commission,  such  indemnification is  against  public  policy as
expressed in the Securities Act and  is, therefore, unenforceable. In the  event
that  a  claim  for indemnification  against  such liabilities  (other  than the
payment by the Registrant of expenses incurred or paid by a director, officer of
controlling person of the  Registrant in the successful  defense of any  action,
suit or proceeding) is asserted by such directors, officer or controlling person
in  connection with the securities being registered, the Registrant will, unless
in the  opinion  of its  counsel  the matter  has  been settled  by  controlling
precedent,  submit to a  court of appropriate  jurisdiction the question whether
such indemnification  by  it  is  against public  policy  as  expressed  in  the
Securities Act and will be governed by the final adjudication of such issue.
 
    The   undersigned  Registrant  hereby  undertakes   that,  for  purposes  of
determining any liability under the Securities Act, (i) the information  omitted
from  the Prospectus  filed as part  of this Registration  Statement in reliance
upon Rule 430A under the  Securities Act and contained  in a form of  Prospectus
filed  by the Registrant pursuant  to Rule 424(b)(1) or  (4) or 497(h) under the
Securities Act shall be deemed to be part of this Registrant Statement as of the
time it  was declared  effective  and (ii)  each post-effective  amendment  that
contains a form of prospectus shall be deemed to be a new Registration Statement
relating  to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.
 
    The undersigned registrant hereby undertakes to provide to the Underwriters,
at the closing  specified in  the Underwriting Agreement,  certificates in  such
denominations  and registered in  such names as required  by the Underwriters to
permit prompt delivery to each purchaser.
 
                                      II-3
<PAGE>
                                   SIGNATURES
 
    Pursuant  to the requirements of the  Securities Act of 1933, the Registrant
has duly caused this Registration  Statement to be signed  on its behalf by  the
undersigned,  thereunder duly authorized in the City of Midland, State of Texas,
on July 25, 1996.
 
                                          COSTILLA ENERGY, INC.
                                          (Registrant)
 
                                          By:                  *
 
                                             -----------------------------------
                                                      Michael J. Grella
                                                PRESIDENT AND CHIEF OPERATING
                                                           OFFICER
 
    Pursuant  to  the  requirements  of   the  Securities  Act  of  1933,   this
Registration Statement has been signed by the following persons on behalf of the
Registrant and in the capacities and on the dates indicated.
 
             SIGNATURE                         TITLE                  DATE
- -----------------------------------  -------------------------  ----------------
 
                     *               Chairman of the Board,
- -----------------------------------   Chief Executive Officer    July 25, 1996
         Cadell S. Liedtke            and Director
 
                     *               President, Chief
- -----------------------------------   Operating Officer and      July 25, 1996
         Michael J. Grella            Director
 
                     *
- -----------------------------------  Executive Vice President    July 25, 1996
        Henry G. Musselman            and Director
 
         /s/ BOBBY W. PAGE           Senior Vice Present,
- -----------------------------------   Treasurer and Chief        July 25, 1996
           Bobby W. Page              Financial Officer
 
                     *
- -----------------------------------  Director                    July 25, 1996
         Jerry J. Langdon
 
                     *
- -----------------------------------  Director                    July 25, 1996
           W.D. Kennedy
 
*By:           /s/ BOBBY W. PAGE
- -----------------------------------
           Bobby W. Page
         ATTORNEY-IN-FACT
 
                                      II-4
<PAGE>
                               INDEX TO EXHIBITS
 
<TABLE>
<CAPTION>
 EXHIBIT                                                                                               SEQUENTIALLY
  NUMBER                                     DESCRIPTION OF EXHIBIT                                    NUMBERED PAGE
- ----------  ----------------------------------------------------------------------------------------  ---------------
<C>         <S>                                                                                       <C>
     *1.1   Form of Underwriting Agreement
   ***3.1   Certificate of Incorporation of the Company
   ***3.2   Bylaws of the Company
   ***4.1   Form  of Notes  or Global Certificate  (included as Exhibit  A to the  form of Indenture
             filed as  Exhibit Number  4.2  to the  Registration Statement  on  Form S-1,  File  No.
             333-     , filed with respect to the Notes)
   ***4.2   Form of Indenture
    **4.3   Form of Stock Certificate
    **5.1   Opinion of Cotton, Bledsoe, Tighe & Dawson, a Professional Corporation
    **6.1   Purchase  and  Sale  Agreement dated  April  3, 1995  by  and between  Parker  & Parsley
             Development L.P.  and  Parker  &  Parsley  Producing L.P.  and  Parker  &  Parsley  Gas
             Processing Co. as Seller and Costilla Petroleum Corporation and Costilla Energy, L.L.C.
             as Purchaser
    **6.2   Purchase  and  Sale  Agreement dated  March  8, 1996  by  and between  Parker  & Parsley
             Development L.P.  and  Parker  &  Parsley  Producing L.P.  and  Parker  &  Parsley  Gas
             Processing Co. as Seller and Costilla Petroleum Corporation and Costilla Energy, L.L.C.
             as Purchaser
   **10.1   Form  of Credit Agreement to  be entered into contemporaneously  with the closing of the
             Offerings between the Company as Borrower and                      as Lender.
  ***10.2   Lease Agreement dated  January 12, 1996  between Independence Plaza,  Ltd. and  Costilla
             Energy, L.L.C.
  ***10.3   Concession  Agreement  dated July  6, 1995  between  the Government  of the  Republic of
             Moldova and the Resource Development Company, Limited.
  ***10.4   Purchase and Joint Exploration Agreement dated February 21, 1996 between the Company and
             Resources Development Limited, L.L.C. (DE).
   **10.5   Consolidation Agreement to be effective contemporaneously with closing of the  Offerings
             to consummate the Corporate Reorganization.
   **10.6   1996 Stock Option Plan.
   **10.7   Outside Directors Stock Option Plan.
  ***10.8   Employment Agreement between the Company and Bobby W. Page effective June 30, 1996.
   **10.9   Employment  Agreement  between  the  Company  and  Cadell  S.  Liedtke  to  be effective
             contemporaneously with the closing of the Offerings.
   **10.10  Employment Agreement  between  the  Company  and  Michael  J.  Grella  to  be  effective
             contemporaneously with the closing of the Offerings.
   **10.11  Employment  Agreement  between  the  Company  and Henry  G.  Musselman  to  be effective
             contemporaneously with the closing of the Offerings.
  ***10.12  Exchange Agreement dated January 5, 1995 between Costilla Petroleum Corporation and Koch
             Oil Company.
  ***10.13  Agreement dated January 2, 1996 between Costilla Petroleum Corporation and Frontier  Oil
             and Refining Company.
  ***12.1   Computation of Ratio of EBITDA to Interest Expense
  ***12.2   Computation of Ratio of Earnings to Fixed Charges
  ***21.1   Subsidiaries of the Registrant
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
 EXHIBIT                                                                                               SEQUENTIALLY
  NUMBER                                     DESCRIPTION OF EXHIBIT                                    NUMBERED PAGE
- ----------  ----------------------------------------------------------------------------------------  ---------------
<C>         <S>                                                                                       <C>
    *23.1   Consent of KPMG Peat Marwick LLP
    *23.2   Consent of Williamson Petroleum Consultants, Inc.
    *23.3   Consent of Elms, Faris & Co., P.C.
   **23.4   Consent  of Cotton, Bledsoe, Tighe & Dawson, a Professional Corporation (such consent is
             included in the opinion filed as Exhibit 5.1 to this Registration Statement)
    *24.1   Power of Attorney
    *24.2   Certified copy of resolution of Board of Directors of Costilla Energy, Inc.  authorizing
             signature pursuant to Power of Attorney
    *27.1   Financial Data Schedule
</TABLE>
 
- ------------------------
*   Filed herewith
**  To be filed by amendment
*** Incorporated by reference to Registration Statement on Form S-1, File No.
    333-      , filed with respect to the Notes



<PAGE>
                                                        [Draft of July 25, 1996]


                              Costilla Energy, Inc.

                                4,000,000 Shares

                                  Common Stock

                             UNDERWRITING AGREEMENT


                                                             _________ ___, 1996

PRUDENTIAL SECURITIES INCORPORATED
RAUSCHER PIERCE REFSNES, INC.
As Representatives of the several Underwriters
c/o Prudential Securities Incorporated
One New York Plaza
New York, New York 10292

Dear Sirs:

     Costilla Energy, Inc., a Delaware corporation (the "Company"), hereby 
confirms its agreement with the several underwriters named in Schedule 1 
hereto (the "Underwriters"), for whom you have been duly authorized to act as 
representatives (in such capacities, the "Representatives"), as set forth 
below. If you are the only Underwriters, all references herein to the 
Representatives shall be deemed to be to the Underwriters.

     It is understood and agreed to by all parties hereof that, prior to or 
concurrently with the Firm Closing Date (as hereinafter defined), the Company 
will issue in a public offering $100 million principal of its Notes (the 
"Notes Offering").

     1.   SECURITIES.  Subject to the terms and conditions herein contained, the
Company agrees to issue and sell to the several Underwriters an aggregate of
4,000,000 shares (the "Firm Securities") of the Company's Common Stock, par
value $.10 per share ("Common Stock").  The Company also proposes to issue and
sell to the several Underwriters not more than 600,000 additional shares of
Common Stock if requested by the Representatives as provided in Section 3 of
this Agreement.  Any and all shares of Common Stock to be purchased by the
Underwriters pursuant to such option are referred to herein as the "Option
Securities," and the Firm Securities and any Option Securities are collectively
referred to herein as the "Securities".


<PAGE>

     2.   REPRESENTATIONS AND WARRANTIES OF THE COMPANY.  The Company and each
of the subsidiaries of the Company appearing on the signature pages hereof (the
"Subsidiary Guarantors") represents and warrants to, and agrees with, each of
the several Underwriters that:

          (a)  A registration statement on Form S-1 (File No. 333-________) with
     respect to the Securities (i) has been prepared by the Company in
     conformity with the requirements of the Securities Act of 1933, as amended
     (the "Act"), and the rules and regulations (the "Rules and Regulations") of
     the Securities and Exchange Commission (the "Commission") thereunder,
     (ii) has been filed with the Commission under the Act and (iii) either has
     become effective under the Act and is not proposed to be amended or is
     proposed to be amended by amendment or post-effective amendment.  If the
     Company does not propose to amend such registration statement and if any
     post-effective amendment to such registration statement has been filed with
     the Commission prior to the execution and delivery of this Agreement, the
     most recent such amendment has been declared effective by the Commission. 
     Copies of such registration statement as amended to date have been
     delivered by the Company to you.  For purposes of this Agreement,
     "Effective Time" means the date and the time as of which such registration
     statement, or the most recent post-effective amendment thereto, if any, was
     declared effective by the Commission; "Effective Date" means the date of
     the Effective Time; "Preliminary Prospectus" means each prospectus included
     in such registration statement, or amendments thereof, before it became
     effective under the Act and any prospectus filed with the Commission by the
     Company with the consent of the Underwriters pursuant to Rule 424(a) of the
     Rules and Regulations prior to the filing of the Prospectus; "Registration
     Statement" means such registration statement, as amended at the Effective
     Time, including any documents incorporated by reference therein and, if the
     Effective Date is on or before the date of this Agreement, all information
     contained in the final prospectus filed with the Commission pursuant to
     Rule 424(b) of the Rules and Regulations ("Rule 424(b)") in accordance with
     Section 5(a) hereof and deemed to be a part thereof as of the Effective
     Time pursuant to the Rules and Regulations and any Rule 462(b) Registration
     Statement (as hereinafter defined); "Prospectus" means the form of
     prospectus relating to the Securities, as first used to confirm sales of
     the Shares; and "described in the Prospectus" or "disclosed in the
     Prospectus" means described or disclosed, as applicable, in the Prospectus;
     "Rule 462(b) Registration Statement" means any registration statement filed
     with the Commission pursuant to Rule 462(b) under the Act (including the
     Registration Statement and any Preliminary Prospectus or Prospectus
     incorporated therein at the time such Registration Statement becomes
     effective).  The Commission has not issued any order preventing or
     suspending the use of any Preliminary Prospectus or the Prospectus.

          (b)  At the Effective Time and at all times subsequent thereto up to
     the Closing Date (as hereinafter defined), the Registration Statement and
     the Prospectus, and any amendments or supplements thereto, conform in all
     material respects with the requirements of the Act and the Rules and
     Regulations, and at the Effective Time the Registration Statement did not
     include any untrue statement of a material fact or omit to state any
     material fact required to be stated therein or necessary to make the
     statements therein not misleading, and the Prospectus, as amended or
     supplemented at the Closing Date, if applicable, did not contain any untrue
     statement of a material fact or omit to state a material fact necessary to


                                     -2-

<PAGE>

     make the statements contained therein, in the light of the circumstances
     under which they were made, not misleading; except that the foregoing does
     not apply to statements or omissions in the Registration Statement or the
     Prospectus, as amended or supplemented if applicable, based upon written
     information furnished to the Company by any Underwriter through you
     specifically for use therein. 

          (c)  The consolidated financial statements included in the
     Registration Statement and Prospectus present fairly the consolidated
     financial position of the Company and its consolidated subsidiaries as at
     the dates indicated and the results of their operations and the changes in
     their consolidated financial position for the periods specified; said
     financial statements have been prepared in conformity with generally
     accepted accounting principles applied on a consistent basis during the
     periods involved, except as indicated therein; and the supporting schedules
     included in the Registration Statement present fairly the information
     required to be stated therein.  The pro forma financial statements set
     forth in the Registration Statement and the Prospectus (the "pro forma
     financial statements") have been prepared in accordance with the applicable
     accounting requirements of Rule 11-02 of Regulation S-X; the pro forma
     adjustments reflected in the pro forma financial statements have been
     properly applied to the historical amounts in the compilation of such
     statements; and the assumptions used in the preparation of the pro forma
     financial statements are, in the opinion of the Company, reasonable.

          (d)  Since the respective dates as of which information is given in
     the Registration Statement and the Prospectus, except as otherwise stated
     therein, (i) there has not been and will not have been any change in the
     capitalization of the Company, or any material adverse change in the
     condition, financial or otherwise, earnings, affairs or business prospects
     of the Company and its subsidiaries considered as a whole, whether or not
     arising in the ordinary course of business, (ii) there have been no
     material transactions entered into by the Company or any of its
     subsidiaries other than those in the ordinary course of business, (iii) the
     Company has not issued or granted any securities, and (iv) the Company has
     not and will not have paid or declared any dividends or other distributions
     of any kind on any class of its capital stock.

          (e)  The Company has been duly incorporated and is validly existing as
     a corporation in good standing under the laws of the State of Delaware with
     corporate power and authority to own, lease and operate its properties and
     conduct its business as described in the Registration Statement; and the
     Company is duly qualified as a foreign corporation to transact business and
     is in good standing in each jurisdiction in which it owns or leases
     properties or in which the conduct of its business requires such
     qualification, except to the extent that the failure to be so qualified or
     be in good standing would not have a material adverse effect on the Company
     and its subsidiaries considered as a whole. 

          (f)  Each of the subsidiaries of the Company has been duly
     incorporated or organized and is validly existing as a corporation or
     limited liability company in good standing under the laws of the
     jurisdiction of its formation, has corporate power and authority to own,
     lease and operate its properties and conduct its business as described in
     the 


                                     -3-

<PAGE>

     Registration Statement and is duly qualified as a foreign corporation
     or limited liability company to transact business and is in good standing
     in each jurisdiction in which it owns or leases properties or in which the
     conduct of its business requires such qualification, except to the extent
     that the failure to be so qualified or be in good standing would not have a
     material adverse effect on the Company and its subsidiaries considered as a
     whole; all of the issued and outstanding capital stock or other equity
     interest of each subsidiary has been duly authorized and validly issued and
     is fully paid and nonassessable, and all such capital stock or other equity
     interest of each subsidiary is owned by the Company, directly or through
     subsidiaries, free and clear of any mortgage, pledge, lien, encumbrance,
     claim or equity and, except as disclosed in the Prospectus, neither the
     Company nor any such subsidiary owns any shares of stock or any other
     equity securities of any corporation or has any equity interest in any
     firm, partnership, association or other entity.

          (g)  Neither the Company nor any of its subsidiaries is (i) in
     violation of its or any of their charters or by-laws or other
     organizational documents or (ii) in default in the performance or
     observance of any obligation, agreement, covenant or condition contained in
     any contract, indenture, mortgage, loan agreement, note, lease or other
     instrument to which it or any of them is a party or by which it or any of
     them or their properties may be bound except to the extent that such
     default would not have a material adverse effect on the Company and its
     subsidiaries considered as a whole; no consent, approval, authorization or
     order of any court or governmental authority or agency is required for the
     consummation by the Company of the transactions contemplated by this
     Agreement, except such as may be required under the Act, the Rules and
     Regulations or state securities or Blue Sky laws; and the execution and
     delivery of this Agreement and the consummation of the transactions
     contemplated herein and the application of the net proceeds from the
     offering and sale of the Securities in the manner set forth in the
     Prospectus under "Use of Proceeds" will not conflict with or constitute a
     breach of, or default under, or result in the creation or imposition of any
     lien, charge or encumbrance upon any property or assets of the Company or
     any of its subsidiaries pursuant to, any material contract, indenture,
     mortgage, loan agreement, note, lease or other instrument to which the
     Company or any of its subsidiaries is a party or by which it or any of them
     may be bound or to which any of the property or assets of the Company or
     any of its subsidiaries is subject, nor will such action result in any
     violation of or conflict with the provisions of the charter or by-laws of
     the Company or any law, administrative regulation or administrative or
     court decree. 

          (h)  The Company and its subsidiaries possess adequate certificates,
     authorities, licenses or permits issued by the appropriate state, federal
     or foreign regulatory agencies or bodies necessary to conduct the business
     now operated by them, and neither the Company nor any of its subsidiaries
     has received any notice of proceedings relating to the revocation or
     modification of any such certificate, authority, license or permit which,
     singly or in the aggregate, if the subject of an unfavorable decision,
     ruling or finding, would materially adversely affect the condition,
     financial or otherwise, earnings, affairs or business prospects of the
     Company and its subsidiaries considered as a whole.


                                     -4-

<PAGE>

          (i)  Except as set forth in the Prospectus, there is no action, suit
     or proceeding before or by any court or governmental agency or body,
     domestic or foreign, now pending or, to the knowledge of the Company,
     threatened against or affecting the Company or any of its subsidiaries,
     which might result in any material adverse change in the condition,
     financial or otherwise, earnings, affairs or business prospects of the
     Company and its subsidiaries considered as a whole, or might materially and
     adversely affect the properties or assets thereof or might materially and
     adversely affect the offering of the Securities; and there are no material
     contracts or other documents which are required to be filed as exhibits to
     the Registration Statement by the Act or by the Rules and Regulations which
     have not been so filed.

          (j)  The Company and each of its subsidiaries has good and defensible
     title to all property and assets owned by it and necessary in the conduct
     of the business of the Company or such subsidiary in each case free and
     clear of all liens, encumbrances and defects except (i) such as are
     referred to in the Prospectus or (ii) such as do not materially adversely
     affect the value of such property to the Company or such subsidiary, and do
     not interfere with the use made and proposed to be made of such property by
     the Company or such subsidiary to an extent that such interference would
     have a material adverse effect on the Company or such subsidiary.

          (k)  This Agreement has been duly authorized, executed and delivered
     by the Company and each of the Subsidiary Guarantors and is a valid and
     binding agreement of the Company and each of the Subsidiary Guarantors
     (subject, as to the enforcement of remedies, to applicable bankruptcy,
     reorganization, insolvency, moratorium or other laws affecting creditors'
     rights generally from time to time in effect and to general equitable
     principles), except as rights to indemnity hereunder may be limited by
     applicable law.

          (l)  The outstanding shares of Common Stock have been, and the
     Securities to be issued and sold by the Company upon such issuance as
     provided herein will be, duly authorized, validly issued, fully paid and
     nonassessable, and will not be subject to any preemptive or similar right. 
     The description of the Common Stock in the Registration Statement and the
     Prospectus is, and at the Closing Date will be, complete and accurate in
     all respects.  Except as set forth in the Prospectus, the Company does not
     have outstanding, and at the Closing Date will not have outstanding, any
     options to purchase, or any rights or warrants to subscribe for, or any
     securities or obligations convertible into, or any contracts or commitments
     to issue or sell, any shares of Common Stock, any shares of capital stock
     or other equity interest of any subsidiary or any such warrants,
     convertible securities or obligations.

          (m)  Neither the filing of the Registration Statement nor the offering
     or sale of the Securities as contemplated by this Agreement gives rise to
     any rights, other than those which have been duly waived or satisfied and
     those pursuant to Article XI of the Regulations of Costilla Energy, L.L.C.,
     for or relating to the registration of any securities of the Company.  The
     pro forma capitalization of the Company as of  the date of the most recent
     balance sheet included in the Prospectus is as set forth in the Prospectus.
     The Company has all requisite 


                                     -5-

<PAGE>

     corporate power and authority to issue, sell, and deliver the Securities 
     in accordance with and upon the terms and conditions set forth in this 
     Agreement and in the Registration Statement and Prospectus.  All 
     corporate action required to be taken by the Company for the 
     authorization, issuance, sale and delivery of the Securities to be sold 
     by the Company hereunder has been validly and sufficiently taken.

          (n)  The Securities are duly authorized for listing, subject to
     official notice of issuance, on the Nasdaq National Market.

          (o)  KPMG Peat Marwick, LLP and Elms, Faris & Co., P.C., who have
     certified certain financial statements of the Company and its subsidiaries,
     are independent public accountants within the meaning of the Securities Act
     and the rules and regulations thereunder.

          (p)  The Company and each of its subsidiaries maintain a system of
     internal accounting controls sufficient to provide reasonable assurances
     that (i) transactions are executed in accordance with management's general
     or specific authorizations; (ii) transactions are recorded as necessary to
     permit preparation of financial statements in conformity with generally
     accepted accounting principles and to maintain asset accountability; (iii)
     access to assets is permitted only in accordance with management's general
     or specific authorization; and (iv) the recorded accountability for assets
     is compared with the existing assets at reasonable intervals and
     appropriate action is taken with respect to any differences.

          (q)  The Company and its subsidiaries own or otherwise possess the
     right to use all patents, trademarks, service marks, trade names and
     copyrights, all applications and registrations for each of the foregoing,
     and all other proprietary rights and confidential information used in the
     conduct of their respective businesses as currently conducted; and neither
     the Company nor any of its subsidiaries has received any notice or is
     otherwise aware, of any infringement of or conflict with the rights of any
     third party with respect to any of the foregoing which, singly or in the
     aggregate, if the subject of an unfavorable decision, ruling or finding,
     would result in a material adverse effect on the Company.

          (r)  The Company and each of its subsidiaries are insured by insurers
     of recognized financial responsibility against such losses and risks and in
     such amounts as are prudent and customary in the businesses in which they
     are engaged; neither the Company nor any of its subsidiaries have been
     refused any insurance coverage sought or applied for; and neither the
     Company nor any of its subsidiaries have any reason to believe that they
     will not be able to renew their existing insurance coverage as and when
     such coverage expires or to obtain similar coverage from similar insurers
     as may be necessary to continue its business at a cost that would not have
     a material adverse effect on the Company.

          (s)  The Company has complied and will comply with all the provisions
     of Section 517.075, Florida Statutes (Chapter 92-198, Laws of Florida) and
     all regulations promulgated thereunder relating to issuers doing business
     in Cuba.


                                     -6-

<PAGE>

          (t)  There are no contracts or other documents which are required to
     be described in the Prospectus or filed as exhibits to the Registration
     Statement by the Act or by the Rules and Regulations which have not been
     described in the Prospectus or filed as exhibits to the Registration
     Statement or incorporated therein by reference as permitted by the Rules
     and Regulations.

          (u)  There has been no storage, disposal, generation, manufacture,
     refinement, transportation, handling or treatment of toxic wastes, medical
     wastes, hazardous wastes or hazardous substances by the Company or any of
     its subsidiaries (or, to the knowledge of the Company, any of their
     predecessors in interest) at, upon or from any of the property now or
     previously owned or leased by the Company or its subsidiaries in violation
     of any applicable law, ordinance, rule, regulation, order, judgment, decree
     or permit, or which would require remedial action under any applicable law,
     ordinance, rule, regulation, order, judgment, decree or permit, except for
     any violation or remedial action which would not have, or could not be
     reasonably likely to have, singularly or in the aggregate with all such
     violations and remedial actions, a material adverse effect on the general
     affairs, management, financial position, stockholders' equity or results of
     operations of the Company and its subsidiaries; there has been no material
     spill, discharge, leak, emission, injection, escape, dumping or release of
     any kind onto such property or into the environment surrounding such
     property of any toxic wastes, medical wastes, solid wastes, hazardous
     wastes or hazardous substances due to or caused by the Company or any of
     its subsidiaries or with respect to which the Company or any of its
     subsidiaries have knowledge, except for any such spill, discharge, leak,
     emission, injection, escape, dumping or release which would not have or
     would not be reasonably likely to have, singularly or in the aggregate with
     all such spills, discharges, leaks, emissions, injections, escapes,
     dumpings and releases, a material adverse effect on the general affairs,
     management, financial position, stockholders' equity or results of
     operations of the Company and its subsidiaries; and the terms "hazardous
     wastes," "toxic wastes," "hazardous substances" and "medical wastes" shall
     have the meanings specified in any applicable local, state, federal and
     foreign laws or regulations with respect to environmental protection.

          (v)  If the Company has elected to rely on Rule 462(b) under the Act
     and the Rule 462(b) Registration Statement has not been declared effective
     (i) the Company has filed a Rule 462(b) Registration Statement in
     compliance with and that is effective upon filing pursuant to Rule 462(b)
     and has received confirmation of its receipt and (ii) the Company has given
     irrevocable instructions for transmission of the applicable filing fee in
     connection with the filing of the Rule 462(b) Registration Statement, in
     compliance with Rule 111 promulgated under the Act or the Commission has
     received payment of such filing fee.

          (w)  The Company has not, directly or indirectly, (i) taken any action
     designed to cause or to result in, or that has constituted or which might
     reasonably be expected to constitute, the stabilization or manipulation of
     the price of any security of the Company to facilitate the sale or resale
     of the Securities or (ii) since the filing of the Registration Statement
     (A) sold, bid for, purchased, or paid anyone any compensation for
     soliciting 


                                     -7-

<PAGE>

     purchases of, the Securities or (B) paid or agreed to pay to any
     person any compensation for soliciting another to purchase any other
     securities of the Company.

          (x)  The Company has not distributed and, prior to the later of (i)
     the Closing Date and (ii) the completion of the distribution of the shares,
     will not distribute any offering material in connection with the offering
     and sale of the shares other than the Registration Statement or any
     amendment thereto, any Preliminary Prospectus or the Prospectus or any
     amendment or supplement thereto, or other materials, if any, permitted by
     the Act.

     3.   PURCHASE, SALE AND DELIVERY OF THE SECURITIES.  (a) On the basis of
     the representations, warranties, agreements and covenants herein contained
     and subject to the terms and conditions herein set forth, the Company
     agrees to issue and sell to each of the Underwriters, and each of the
     Underwriters, severally and not jointly, agrees to purchase from the
     Company, at a purchase price of $____ per share, the number of Firm
     Securities set forth opposite the name of such Underwriter in Schedule 1
     hereto.  One or more certificates in definitive form for the Firm
     Securities that the several Underwriters have agreed to purchase hereunder,
     and in such denomination or denominations and registered in such name or
     names as the Representatives request upon notice to the Company at least 48
     hours prior to the Firm Closing Date, shall be delivered by or on behalf of
     the Company to the Representatives for the respective accounts of the
     Underwriters, against payment by or on behalf of the Underwriters of the
     purchase price therefor by wire transfer in same-day funds (the "Wired
     Funds") to the account of the Company.  Such delivery of and payment for
     the Firm Securities shall be made at the offices of Baker & Botts, L.L.P.
     ("Counsel for the Underwriters"), One Shell Plaza, 910 Louisiana, Houston,
     Texas 77002, at 10:00 a.m., Houston time, on the fourth full business day
     following the date of this Agreement or at such other place, time or date
     as the Representatives and the Company may agree upon or as the
     Representatives may determine pursuant to Section 9 hereof, such time and
     date of deliver against payment being herein referred to as the "Firm
     Closing Date".  The Company will make such certificate or certificates for
     the Firm Securities available for checking and packaging by the
     Representatives at the offices in New York, New York of the Company's
     transfer agent or registrar or of Prudential Securities Incorporated at
     least 24 hours prior to the Firm Closing Date.

          (b)  For the purpose of covering any over-allotments in connection
     with the distribution and sale of the Firm Securities as contemplated by
     the Prospectus, the Company hereby grant to the several Underwriters an
     option to purchase, severally and not jointly, the Option Securities The
     purchase price to be paid for any Option Securities shall be the same price
     per share as the price per share for the Firm Securities set forth above in
     paragraph (a) of this Section 3.  The option granted hereby may be
     exercised as to all or any part of the Option Securities from time to time
     within 30 days after the date of the Prospectus (or, if such 30th day shall
     be a Saturday or Sunday or a holiday, on the next business day thereafter
     when the New York Stock Exchange is open for trading).  The Underwriters
     shall not be under an obligation to purchase any of the Option Securities
     prior to the exercise of such option.  The Representatives may from time to
     time exercise the option granted hereby by giving notice in writing or by
     telephone (confirmed in writing) to the Company setting forth 


                                     -8-

<PAGE>


     the aggregate number of Option Securities as to which the several 
     Underwriters are then exercising the option and the date and time for 
     delivery of and payment for such Option Securities.  Any such date of 
     delivery shall be determined by the Representatives but shall not be 
     earlier than two business days or later than five business days after 
     such exercise of the option and, in any event, shall not be earlier than 
     the Firm Closing Date.  The time and date set forth in such notice, or 
     such other time on such other date as the Representatives and Company 
     may agree upon or as the Representatives may determine pursuant to 
     Section 9 hereof, is herein called the "Option Closing Date" with 
     respect to such Option Securities, and the Firm Closing Date and the 
     Option Closing Date are sometimes each referred to herein as a "Closing 
     Date."  Upon exercise of the option as provided herein, the Company 
     shall become obligated to sell to each of the several Underwriters, and, 
     subject to the terms and conditions herein set forth, each of the 
     Underwriters (severally and not jointly) shall become obligated to 
     purchase from the Company, the same percentage of the total number of 
     the Option Securities as to which the several Underwriters are then 
     exercising the option as such Underwriter is obligated to purchase of 
     the aggregate number of Firm Securities, as adjusted by the 
     Representatives in such manner as they deem advisable to avoid 
     fractional shares.  If the option is exercised as to all or any portion 
     of the Option Securities, one or more certificates in definitive form 
     for such Option Securities, and payment therefor, shall be delivered on 
     the related Option Closing Date in the manner, and upon the terms and 
     conditions, set forth in paragraph (a) of this Section 3, except that 
     reference therein to the Firm Securities and the Firm Closing Date shall 
     be deemed, for purposes of this paragraph (b), to refer to such Option 
     Securities and Option Closing Date, respectively.

          (c)  The Company hereby acknowledges that the wire transfer by or on
     behalf of the Underwriters of the purchase price for any Securities does
     not constitute closing of a purchase and sale of the Securities.  Only
     execution and delivery of a receipt for Securities by the Underwriters
     indicates completion of the closing of a purchase of the Securities from
     the Company.  Furthermore, in the event that the Underwriters wire funds to
     the Company prior to the completion of the closing of a purchase of
     Securities, the Company hereby acknowledges that until the Underwriters
     execute and deliver a receipt for the Securities, by facsimile or
     otherwise, the Company will not be entitled to the wired funds and shall
     return the wired funds to the Underwriters as soon as practicable (by wire
     transfer of same-day funds) upon demand.  In the event that the closing of
     a purchase of Securities is not completed and the wire funds are not
     returned by the Company to the Underwriters on the same day the wired funds
     were received by the Company, the Company agrees to pay to the Underwriters
     in respect of each day the wire funds are not returned by it, in same-day
     funds, interest on the amount of such wire funds in an amount representing
     the Underwriters' cost of financing as reasonably determined by Prudential
     Securities Incorporated.

          (d)  It is understood that either of you, individually and not as one
     of the Representatives, may (but shall not be obligated to) make payment on
     behalf of any Underwriter or Underwriters for any of the Securities to be
     purchased by such Underwriter or Underwriters.  No such payment shall
     relieve such Underwriter or Underwriters from any of its or their
     obligation hereunder.


                                     -9-

<PAGE>

     4.   OFFERING BY THE UNDERWRITERS.  Upon your authorization of the release
of the Firm Securities, the several Underwriters propose to offer the Firm
Securities for sale to the public upon the terms set forth in the Prospectus.

     5.   COVENANTS OF THE COMPANY.  The Company covenants and agrees with each
of the Underwriters that:

          (a)  The Company will use its best efforts to cause the Registration
     Statement, if not effective at the time of execution of this Agreement, and
     any amendments thereto to become effective as promptly as possible.  If
     required, the Company will file the Prospectus that constitutes a part
     thereof and any amendment or supplement thereto with the Commission in the
     manner and within the time period required by Rules 434 and 424(b) under
     the Act.  During any time when a prospectus relating to the Securities is
     required to be delivered under the Act, the Company (i) will comply with
     all requirements imposed upon it by the Act and the rules and regulations
     of the Commission thereunder to the extent necessary to permit the
     continuance of sales of or dealings in the Securities in accordance with
     the provisions hereof and of the Prospectus, as then amended or
     supplemented, and (ii) will not file with the Commission the Prospectus or
     the amendment referred to in Section 2(a) hereof, any amendment or
     supplement to such Prospectus or any amendment to the Registration
     Statement or any Rule 462(b) Registration Statement of which the
     Representatives previously have been advised and furnished with a copy for
     a reasonable period of time prior to the proposed filing and as to which
     filing the Representatives shall not have given their consent.  The Company
     will prepare and file with the Commission, in accordance with the Rules and
     Regulations, promptly upon request by the Representatives or counsel for
     the Underwriters, any amendments to the Registration Statement or
     amendments or supplements to the Prospectus that may be necessary or
     advisable in connection with the distribution of the Securities by the
     several Underwriters, and will use its best efforts to cause any such
     amendment to the Registration Statement to be declared effective by the
     Commission as promptly as possible.  The Company will advise the
     Representatives, promptly after receiving notice thereof, of the time when
     the Registration Statement or any amendment thereto has been filed or
     declared effective or the Prospectus or any amendment or supplement thereto
     has been filed and will provide evidence satisfactory to the
     Representatives of each such filing or effectiveness.

          (b)  The Company will advise the Representatives, promptly after
     receiving notice or obtaining knowledge thereof, of (i) the issuance by the
     Commission of any stop order suspending the effectiveness of the
     Registration Statement or any Rule 462(b) Registration Statement or any
     amendment thereto or any order preventing or suspending the use of any
     Preliminary Prospectus or the Prospectus or any amendment or supplement
     thereto, (ii) the suspension of the qualification of the Securities for
     offering or sale in any jurisdiction, (iii) the institution, threatening or
     contemplation of any proceeding for any such purpose or (iv) any request
     made by the Commission for amending the Registration Statement or any Rule
     462(b) Registration Statement, for amending or supplementing the Prospectus
     or for additional information.  The Company will use its best efforts to
     prevent the issuance of any 


                                     -10-

<PAGE>

     such stop order and, if any such stop order is issued, to obtain the 
     withdrawal thereof as promptly as possible.

          (c)  The Company will arrange for the qualification of the Securities
     for offering and sale under the securities or Blue Sky laws of such
     jurisdictions as the Representatives may designate and will continue such
     qualifications in effect for as long as may be necessary to complete the
     distribution of the Securities, PROVIDED, HOWEVER, that in connection
     therewith the Company shall not be required to qualify as a foreign
     corporation or to execute a general consent to service of process in any
     jurisdiction.

          (d)  If, at any time prior to the later of (i) the final date when a
     prospectus relating to the Securities is required to be delivered under the
     Act or (ii) the Option Closing Date, any event occurs as a result of which
     the Prospectus, as then amended or supplemented, would include any untrue
     statement of a material fact or omit to state a material fact in order to
     make the statements therein, in the light of the circumstances under which
     they were made, not misleading, or if for any other reason it is necessary
     at any time to amend or supplement the Prospectus to comply with the Act or
     the rules or regulations of the Commission thereunder, the Company will
     promptly notify the Representatives thereof and, subject to Section 5(a)
     hereof, will prepare and file with the Commission, at the Company's
     expense, an amendment to the Registration Statement or an amendment or
     supplement to the Prospectus that corrects such statement or omission or
     effects such compliance.

          (e)  The Company will, without charge, provide (i) to the
     Representatives and to counsel for the Underwriters a signed copy of the
     registration statement originally filed with respect to the Securities and
     each amendment thereto (in each case including exhibits thereto), (ii) to
     each other Underwriter, a conformed copy of such registration statement or
     any Rule 462(b) Registration Statement and each amendment thereto (in each
     case without exhibits thereto) and (iii) so long as a prospectus relating
     to the Securities is required to be delivered under the Act, as many copies
     of each Preliminary Prospectus or the Prospectus or any amendment or
     supplement thereto as the Representatives may reasonably request; without
     limiting the application of clause (iii) of this sentence, the Company, not
     later than (A) 6:00 P.M., New York City time, on the date of determination
     of the public offering price, if such determination occurred at or prior to
     10:00 A.M., New York City time, on such date or (B) 2:00 P.M., New York
     City time, on the business day following the date of determination of the
     public offering price, if such determination occurred after 10:00 A.M., New
     York City time, on such date, will deliver to the Underwriters, without
     charge, as many copies of the Prospectus and any amendment or supplement
     thereto as the Representatives may reasonably request for purposes of
     confirming orders that are expected to settle on the Firm Closing Date. 
     The Company will provide or cause to be provided to each of the
     Representatives, and to each Underwriter that so requests in writing, a
     copy of each report on Form SR filed by the Company as required by Rule 463
     under the Act.

          (f)  The Company, as soon as practicable, will make generally
     available to its securityholders and to the Representatives a consolidated
     earnings statement of the Company 


                                     -11-

<PAGE>


     and its subsidiaries that satisfies the provisions of Section 11(a) of the
     Act and Rule 158 thereunder.

          (g)  The Company will apply the net proceeds from the sale of the
     Securities as set forth under "Use of Proceeds" in the Prospectus.

          (h)  The Company will not, directly or indirectly, and will cause 
     its stockholders, directors and officers to not, without the prior
     written consent of Prudential Securities Incorporated, on behalf of the
     Underwriters, offer, sell, offer to sell, contract to sell, pledge, grant
     any option to purchase or otherwise sell or dispose (or announce any offer,
     sale, offer of sale, contract of sale, pledge, grant of any option to
     purchase or other sale or disposition) of any shares of Common Stock or any
     securities convertible into, or exchangeable or exercisable for, shares of
     Common Stock for a period of 180 days after the date hereof, except
     pursuant to this Agreement and except for the grant of options pursuant to 
     the Company's employee stock option plans described in the Prospectus and 
     the exercise and/or sale of Common Stock by nonaffiliates of the Company 
     acquired pursuant to the exercise of such options.

          (i)  The Company will not, directly or indirectly, (i) take any action
     designed to cause or to result in, or that has constituted or which might
     reasonably be expected to constitute, the stabilization or manipulation of
     the price of any security of the Company to facilitate the sale or resale
     of the Securities or (ii) (A) sell, bid for, purchase, or pay anyone any
     compensation for soliciting purchases of, the Securities or (B) pay or
     agree to pay to any person any compensation for soliciting another to
     purchase any other securities of the Company (except for the sale of
     Securities by the Selling Securityholders under this Agreement).

          (j)  The Company will obtain the agreements described in Section 7(f)
     hereof prior to the Firm Closing Date.

          (k)  If at any time during the 25-day period after the Registration
     Statement becomes effective or the period prior to the Option Closing Date,
     any rumor, publication or event relating to or affecting the Company shall
     occur as a result of which in your opinion the market price of the Common
     Stock has been or is likely to be materially affected (regardless of
     whether such rumor, publication or event necessitates a supplement to or
     amendment of the Prospectus), the Company will, after notice from you
     advising the Company to the effect set forth above, forthwith prepare,
     consult with you concerning the substance of, and disseminate a press
     release or other public statement, reasonably satisfactory to you,
     responding to or commenting on such rumor, publication or event.

          (l)  The Company will use its best efforts to cause the Securities to
     be duly included for quotation on the Nasdaq Stock Market's National Market
     (the "Nasdaq National Market") prior to the Firm Closing Date.  The Company
     will ensure that the Securities remain included for quotation on the Nasdaq
     National Market following the Firm Closing Date.


                                     -12-


<PAGE>

          (m)  If the Company elects to rely on Rule 462(b), the Company shall
     both file a Rule 462(b) Registration Statement with the Commission in
     compliance with Rule 462(b) and pay the applicable fees in accordance with
     Rule 111 promulgated under the Act by the earlier of (i) 10:00 P.M. Eastern
     time on the date of this Agreement and (ii) the time confirmations are sent
     or given, as specified by Rule 462(b)(2).

     6.   EXPENSES.  The Company will pay all costs and expenses incident to the
performance of its obligations under this Agreement, whether or not the
transactions contemplated herein are consummated or this Agreement is terminated
pursuant to Section 11 hereof, including all costs and expenses incident to (i)
the printing or other production of documents with respect to the transactions,
including any costs of printing the Registration Statement (including financial
statements and exhibits), any Rule 462(b) Registration Statement, the
Prospectus, each preliminary prospectus and all amendments and supplements to
any of them prior to or during the period specified in Section 5(b) (including,
without limitation, the deliveries thereof pursuant to Section 5(d)), this
Agreement and any blue sky memoranda, (ii) all arrangements relating to the
delivery to the Underwriters of copies of the foregoing documents, (iii) the
fees and disbursements of the counsel, the accountants and any other experts or
advisors retained by the Company, (iv) preparation, issuance and delivery to the
Underwriters of any certificates evidencing the Securities, including transfer
agent's and registrar's fees, (v) the qualification of the Securities under
state securities and blue sky laws, including filing fees and fees and
disbursements of counsel for the Underwriters relating thereto, (vi) the filing
fees of the Commission and the National Association of Securities Dealers, Inc.
relating to the Securities, (vii) any quotation of the Securities on the Nasdaq
National Market and, (viii) any meetings with prospective investors in the
Securities (other than as shall have been specifically approved by the
Representatives to be paid for by the Underwriters).  If the sale of the
Securities provided for herein is not consummated because any condition to the
obligations of the Underwriters set forth in Section 7 hereof is not satisfied,
because this Agreement is terminated pursuant to Section 11 hereof or because of
any failure, refusal or inability on the part of the Company to perform all
obligations and satisfy all conditions on its part to be performed or satisfied
hereunder other than by reason of a default by any of the Underwriters, the
Company will reimburse the Underwriters severally upon demand for all out-of-
pocket expenses (including reasonable counsel fees and disbursements) that 
shall have been incurred by them in connection with the proposed purchase and 
sale of the Securities.  The Company shall not in any event be liable to any 
of the Underwriters for the loss of anticipated profits from the transactions 
covered by this Agreement.

     7.   CONDITIONS OF THE UNDERWRITERS' OBLIGATIONS.  The obligations of the
several Underwriters to purchase and pay for the Firm Securities shall be
subject, in the Representatives' sole discretion, to the accuracy of the
representations and warranties of the Company contained herein as of the date
hereof and as of the Firm Closing Date, as if made on and as of the Firm Closing
Date, to the accuracy of the statements of the Company's officers made pursuant
to the provisions hereof, to the performance by the Company of its covenants and
agreements hereunder and to the following additional conditions:

          (a)  The Registration Statement shall have become effective (or if a
     post-effective amendment is required to be filed under the Act, such
     post-effective amendment shall have become effective) not later than 5:00
     p.m., New York time, on the date of this Agreement, 


                                     -13-

<PAGE>

     and, if the Company has elected to rely upon Rule 462(b), the Rule 
     462(b) Registration Statement shall have been declared effective not 
     later than the earlier of (i) 11:00 A.M., New York City time, on the 
     date on which the amendment to the registration statement originally 
     filed with respect to the Securities or to the Registration Statement, 
     as the case may be, containing information regarding the initial public 
     offering price of the Securities has been filed with the Commission and 
     (ii) the time confirmations are sent or given as specified by Rule 
     462(b)(2), or with respect to the Registration Statement, or such later 
     time or date as shall have been consented to by you; and no stop order 
     suspending the effectiveness of the Registration Statement shall have 
     been issued and no proceedings for that purpose shall have been 
     instituted, or to the knowledge of the Company or you, shall be 
     contemplated by the Commission. 

          (b)  The Representatives shall have received an opinion, dated the
     Firm Closing Date, of Cotton, Bledsoe, Tighe & Dawson, a Professional
     Corporation ("Counsel for the Company"), to the effect that:

               (i)  The Company has been duly incorporated and is validly
          existing as a corporation in good standing under the laws of Delaware
          with full corporate power and authority to own, lease and operate its
          properties and conduct its business as described in the Registration
          Statement; and the Company is duly qualified as a foreign corporation
          to transact business and, to the best of such counsel's knowledge and
          information, is in good standing in each jurisdiction which requires
          such qualification wherein it owns or leases properties or conducts 
          business, except where the failure to so qualify would not have a 
          material adverse effect on the properties, prospects, condition 
          (financial or otherwise) or results of operations of the Company 
          and its subsidiaries taken as a whole.

               (ii) Each of the subsidiaries of the Company has been duly
          incorporated or organized and is validly existing as a corporation or
          limited liability company in good standing under the laws of the
          jurisdiction of its formation, has corporate power and authority to
          own, lease and operate its properties and conduct its business as
          described in the Registration Statement, and, to the best of such
          counsel's knowledge and information, is duly qualified as a foreign
          corporation or limited liability company to transact business and is
          in good standing in each jurisdiction which requires such
          qualification wherein it owns or leases properties or conducts 
          business, except where the failure to so qualify would not have a 
          material adverse effect on the properties, prospects, condition 
          (financial or otherwise) or results of operations of the Company 
          and its subsidiaries taken as a whole; all of the issued and
          outstanding capital stock or other equity interest of each subsidiary
          has been duly authorized and validly issued and is fully paid and
          non-assessable, and, except as otherwise set forth in the Registration
          Statement, all of such capital stock or other equity interest, to the
          best of such counsel's knowledge and information, is owned by the
          Company, directly or indirectly, free and clear of any mortgage,
          pledge, lien, encumbrance, claim or equity. 

               (iii)     All of the outstanding shares of capital stock of the
          Company have been duly authorized and are validly issued, fully paid
          and nonassessable.  To the 


                                     -14-

<PAGE>


          best of such counsel's knowledge, neither the filing of the 
          Registration Statement nor the offering or sale of the Securities 
          as contemplated by this Agreement gives rise to any rights, other 
          than those which have been waived or satisfied and those pursuant 
          to Article XI of the Regulations of Costilla Energy, L.L.C., for or 
          relating to the registration of any securities of the Company or 
          any of its subsidiaries, and, to the best of such counsel's 
          knowledge, no person or entity (other than the Underwriters) has 
          the right, contractual or otherwise, to cause the Company to sell 
          or otherwise issue to such person or entity, or permit such person 
          or entity to underwrite the sale of, any of the Securities.  The 
          authorized equity capitalization of the Company as of  the date of 
          the most recent balance sheet included or incorporated by reference 
          in the Prospectus is as set forth in the Prospectus, and the 
          Securities conform as to legal matters to the description thereof 
          contained in the Prospectus.  The Company has all requisite 
          corporate power and authority to issue, sell and deliver the 
          Securities in accordance with and upon the terms and conditions set 
          forth in this Agreement and in the Registration Statement and 
          Prospectus and upon delivery of the Securities against payment 
          therefor in accordance with this Agreement, the Securities will be 
          validly issued, fully paid and nonassessable.

               (iv) There are no preemptive or other rights to subscribe for or
          to purchase, nor any restriction upon the voting or transfer of, any
          of the Securities.

               (v)  This Agreement has been duly authorized, executed and
          delivered by the Company and the Subsidiary Guarantors.

               (vi) The Registration Statement is effective under the Act and,
          to the best of such counsel's knowledge and information, no stop order
          suspending the effectiveness of the Registration Statement has been
          issued under the Act or proceedings therefor initiated or threatened
          by the Commission.  All required filings by the Company under Rule
          424(b) of the Rules and Regulations have been timely made.

               (vii)     Statements set forth in the Prospectus under the
          headings "Business and Properties--Regulation" and "Description of
          Capital Stock," in the Registration Statement, insofar as such
          statements constitute a summary of the legal matters, documents or
          proceedings referred to therein fairly present the information called
          for with respect to such legal matters, documents and proceedings.

               (viii)    No consent, approval, authorization or order of any
          court or governmental authority or agency is required in connection
          with the transactions contemplated by this Agreement, except such as
          may be required under the Act, the Rules and Regulations or state
          securities or Blue Sky laws and such other approvals (specified in
          such opinion) as have been obtained; and, to the best of such
          counsel's knowledge and information, the execution and delivery of
          this Agreement, the issue and sale of the Securities being delivered
          on such Closing Date by the Company and the compliance by the Company
          with all of the provisions of this Agreement and the 


                                     -15-

<PAGE>

          consummation of the transactions contemplated herein will not 
          conflict with or constitute a breach of, or default under, or 
          result in the creation or imposition of any lien, charge or 
          encumbrance upon any property or assets of the Company or any of 
          its subsidiaries pursuant to, any contract, indenture, mortgage, 
          loan agreement, note, lease or other instrument to which the 
          Company or any of its subsidiaries is a party or by which it or any 
          of them may be bound or to which any of the property or assets of 
          the Company or any of its subsidiaries is subject; nor will such 
          action result in any violation of the provisions of the charter or 
          by-laws of the Company, or any law, administrative regulation or 
          administrative or court decree. 

               (ix) After due inquiry, such counsel does not know of any legal
          or governmental proceeding pending or threatened to which the Company
          or any of its subsidiaries is a  party or to which any of the
          properties of the Company is subject that is required to be described
          in the Registration Statement or the Prospectus and is not so
          described or of any contract or other document that is required to be
          described in the Registration Statement or the Prospectus or to be
          filed as an exhibit to the Registration Statement that is not so
          described or filed as required.

               (x)  The Registration Statement, any Rule 462(b) Registration
          Statement and the Prospectus and any further amendments or supplements
          thereto made by the Company at the time the Registration Statement and
          each amendment thereto became effective (except that no opinion need
          be expressed as to the financial statements or notes thereto and other
          financial and statistical data contained therein) complied as to form
          in all material respects with the applicable requirements of the Act
          and the Rules and Regulations.

          Such opinion shall also contain a statement that such counsel has no
     reason to believe that (i) the Registration Statement, as of the Effective
     Time, or any amendment thereto (other than the engineering data, financial
     statements and notes thereto and the other engineering, financial and
     statistical data contained therein, as to which such counsel need not
     comment), at the time it became effective, contained any untrue statement
     of a material fact or omitted to state any material fact required to be
     stated therein or necessary in order to make the statements therein not
     misleading, or (ii) the Prospectus or any supplement or amendment thereto
     (other than the engineering data, financial statements and notes thereto
     and the other engineering, financial and statistical data contained
     therein, as to which such counsel need not comment), on the Firm Closing
     Date or at the time such Prospectus or supplement or amendment thereto was
     issued contains or contained any untrue statement of a material fact or
     omits or omitted to state any material fact required to be stated therein
     or necessary in order to make the statements therein, in light of the
     circumstances under which they were made, not misleading.

          (c)  The Representatives shall have received an opinion, dated the
     Firm Closing Date, of Counsel for the Underwriters, with respect to the
     issuance and sale of the Firm Securities, the Registration Statement and
     the Prospectus, and such other related matters as the Representatives may
     reasonably require, and the Company shall have furnished to such 


                                     -16-

<PAGE>


     counsel such documents as they may reasonably request for the purpose of 
     enabling them to pass upon such matters.  In rendering such opinion, 
     such counsel may rely as to all matters of law upon the opinion of 
     Counsel for the Company referred to in paragraph (b) above.

          (d)  The Representatives shall have received from KPMG Peat Marwick,
     LLP a letter or letters dated, respectively, the date hereof and the Firm
     Closing Date, in form and substance satisfactory to the Representatives, to
     the effect that:

               (i)    they are independent accountants with respect to the 
          Company and its consolidated subsidiaries within the meaning of the 
          Act and the applicable Rules and Regulations;

               (ii)   in their opinion, the audited consolidated financial
          statements and schedules and pro forma financial statements examined
          by them and included in the Registration Statement and the Prospectus
          comply in form in all material respects with the applicable accounting
          requirements of the Act and the related published rules and
          regulations;

               (iii)  on the basis of a reading of the latest available
          interim unaudited consolidated condensed financial statements of the
          Company and its consolidated subsidiaries, carrying out certain
          specified procedures (which do not constitute an examination made in
          accordance with generally accepted auditing standards) that would not
          necessarily reveal matters of significance with respect to the
          comments set forth in this paragraph (iii), a reading of the minute
          books of the shareholders, the board of directors and any committees
          thereof of the Company and each of its consolidated subsidiaries, and
          inquiries of certain officials of the Company and its consolidated
          subsidiaries who have responsibility for financial and accounting
          matters, nothing came to their attention that caused them to believe
          that:

                (A)   the unaudited consolidated condensed financial
          statements of the Company and its consolidated subsidiaries included
          in the Registration Statement and the Prospectus do not comply in form
          in all material respects with the applicable accounting requirements
          of the Act and the Rules and Regulations or are not in conformity with
          generally accepted accounting principles applied on a basis
          substantially consistent with that of the audited consolidated
          financial statements included in the Registration Statement and the
          Prospectus; or

               (B)    at a specified date not more than five days prior to the
          date of such letters, there was any change in the consolidated capital
          stock or any increase in consolidated long-term debt of the Company
          and its subsidiaries or any decrease in the consolidated net current
          assets or members' capital of the Company and its subsidiaries or any
          increases or decreases in any other items specified by the
          Underwriters, in each case as compared with the amounts shown on the
          most recent balance sheet of the Company and its subsidiaries included
          or incorporated by reference in the Registration Statement and
          Prospectus or, during the period from the 


                                     -17-

<PAGE>

          date of such balance sheet to a specified date not more than five 
          days prior to the date of such letters, there were any decreases, 
          as compared with the corresponding period in the preceding year, in 
          consolidated net revenues or the total or per share amounts of 
          consolidated net income of the Company and its subsidiaries or any 
          increases or decreases in any other items specified by the 
          Underwriters, except in each such case as set forth in or 
          contemplated by the Registration Statement and Prospectus or except 
          for such exceptions enumerated in such letters as shall have been 
          agreed to by the Underwriters and the Company;

               (iv) In addition to the examination referred to in their report
          included or incorporated by reference in the Registration Statement
          and the Prospectus, and the specified procedures referred to in clause
          (iii) above, they have carried out certain other specified procedures,
          not constituting an audit, with respect to certain amounts,
          percentages and financial information which are included in the
          Registration Statement and Prospectus and which are specified by the
          Underwriters, and have found such amounts, percentages and financial
          information to be in agreement with the relevant accounting and
          financial records of the Company and its subsidiaries identified in
          such letters; and

               (v)  on the basis of a reading of the unaudited pro forma
          consolidated condensed financial statements included in the
          Registration Statement and the Prospectus, carrying out certain
          specified procedures that would not necessarily reveal matters of
          significance with respect to the comments set forth in this paragraph
          (v), inquiries of certain officials of the Company and its
          consolidated subsidiaries and Parker & Parsley Development L.P. who
          have responsibility for financial and accounting matters and proving
          the arithmetic accuracy of the application of the pro forma
          adjustments to the historical amounts in the unaudited pro forma
          consolidated condensed financial statements, nothing came to their
          attention that caused them to believe that the unaudited pro forma
          consolidated condensed financial statements do not comply in form in
          all material respects with the applicable accounting requirements of
          Rule 11-02 of Regulation S-X or that the pro forma adjustments have
          not been properly applied to the historical amounts in the compilation
          of such statements.

          In the event that the letters referred to above set forth any such
     changes, decreases or increases, it shall be a further condition to the
     obligations of the Underwriters that (A) such letters shall be accompanied
     by a written explanation of the Company as to the significance thereof,
     unless the Representatives deem such explanation unnecessary, and (B) such
     changes, decreases or increases do not, in the sole judgment of the
     Representatives, make it impractical or inadvisable to proceed with the
     purchase and delivery of the Securities as contemplated by the Registration
     Statement, as amended as of the date hereof.

          References to the Registration Statement and the Prospectus in this
     paragraph (d) with respect to either letter referred to above shall include
     any amendment or supplement thereto at the date of such letter.


                                     -18-

<PAGE>

          (e)  You shall have received a certificate, dated the Firm Closing
     Date of the principal executive officer and the principal financial or
     accounting officer of the Company to the effect that:

               (i)    the representations and warranties of the Company in this
          Agreement are true and correct as if made on and as of the Firm
          Closing Date; the Registration Statement, as amended as of the Firm
          Closing Date, does not include any untrue statement of a material fact
          or omit to state any material fact necessary to make the statements
          therein not misleading, and the Prospectus, as amended or supplemented
          as of the Firm Closing Date, does not include any untrue statement of
          a material fact or omit to state any material fact necessary in order
          to make the statements therein, in the light of the circumstances
          under which they were made, not misleading; and the Company has
          performed all covenants and agreements and satisfied all conditions on
          its part to be performed or satisfied at or prior to the Firm Closing
          Date;

               (ii)   no stop order suspending the effectiveness of the
          Registration Statement or any amendment thereto has been issued, and
          no proceedings for that purpose have been instituted or threatened or,
          to the best of the Company's knowledge, are contemplated by the
          Commission; and

               (iii)  subsequent to the respective dates as of which
          information is given in the Registration Statement and the Prospectus,
          neither the Company nor any of its subsidiaries has sustained any
          material loss or interference with their respective businesses or
          properties from fire, flood, hurricane, accident or other calamity,
          whether or not covered by insurance, or from any labor dispute or any
          legal or governmental proceeding, and there has not been any material
          adverse change, or any development involving a prospective material
          adverse change, in the condition (financial or otherwise), management,
          business prospects, net worth or results of operations of the Company
          or any of its subsidiaries, except in each case as described in or
          contemplated by the Prospectus (exclusive of any amendment or
          supplement thereto).

          (f)  You shall have received from each person who is an officer of the
     Company or who owns more than __% of the outstanding shares of Common Stock
     an agreement to the effect that such person will not, directly or
     indirectly, without the prior written consent of Prudential Securities
     Incorporated, on behalf of the Underwriters, offer, sell, offer to sell,
     contract to sell, pledge, grant any option to purchase or otherwise sell or
     dispose (or announce any offer, sale, offer of sale, contract of sale,
     pledge, grant of an option to purchase or other sale or disposition) of any
     shares of Common Stock or any securities convertible into, or exchangeable
     or exercisable for, shares of Common Stock for a period of 180 days after
     the date of this Agreement.

          (g)  On or before the Firm Closing Date, the Representatives and
     counsel for the Underwriters shall have received such further certificates,
     documents or other information as they may have reasonably requested from
     the Company.


                                     -19-

<PAGE>
          (h)  Prior to the commencement of the offering of the Securities, the
     Securities shall have been included for trading on the Nasdaq National
     Market.

          (i)  On or prior to the Firm Closing Date, the closing contemplated
     pursuant to the  Notes Offering shall have occurred.

     All opinions, certificates, letters and documents delivered pursuant to
this Agreement will comply with the provisions hereof only if they are
reasonably satisfactory in all material respects to the Representatives and
counsel for the Underwriters.  The Company shall furnish to the Representatives
such conformed copies of such opinions, certificates, letters and documents in
such quantities as the Representatives and counsel for the Underwriters shall
reasonably request.

     The respective obligations of the several Underwriters to purchase and pay
for any Option Securities shall be subject, in their discretion, to each of the
foregoing conditions to purchase the Firm Securities, except that all references
to the Firm Securities and the Firm Closing Date shall be deemed to refer to
such Option Securities and the related Option Closing Date, respectively.

     8.   INDEMNIFICATION AND CONTRIBUTION.  (a) Each of the Company and the
     Subsidiary Guarantors, jointly and severally, agrees to indemnify and hold
     harmless each Underwriter and each person, if any, who controls any
     Underwriter within the meaning of Section 15 of the Act or Section 20 of
     the Securities Exchange Act of 1934 (the "Exchange Act"), against any
     losses, claims, damages or liabilities, joint or several, to which such
     Underwriter or such controlling person may become subject under the Act or
     otherwise, insofar as such losses, claims, damages or liabilities (or
     actions in respect thereof) arise out of or are based upon:

               (i)  any untrue statement or alleged untrue statement made by the
          Company in Section 2 of this Agreement,

               (ii) any untrue statement or alleged untrue statement of any
          material fact contained in (A) the Registration Statement or any
          amendment thereto, any Preliminary Prospectus or the Prospectus or any
          amendment or supplement thereto or (B) any application or other
          document, or any amendment or supplement thereto, executed by the
          Company or based upon written information furnished by or on behalf of
          the Company filed in any jurisdiction in order to qualify the
          Securities under the securities or blue sky laws thereof or filed with
          the Commission or any securities association or securities exchange
          (each an "Application"),

               (iii) the omission or alleged omission to state in the 
          Registration Statement or any amendment thereto, any Preliminary
          Prospectus or the Prospectus or any amendment or supplement thereto,
          or any Application a material fact required to be stated therein or
          necessary to make the statements therein not misleading, or

               (iv) any untrue statement or alleged untrue statement of any
          material fact contained in any audio or visual materials used in
          connection with the marketing of the Securities, including without
          limitation, slides, videos, films or tape recordings,

                                     -20- 
<PAGE>

     and will reimburse, as incurred, each Underwriter and each such controlling
     person for any legal or other expenses reasonably incurred by such
     Underwriter or such controlling person in connection with investigating,
     defending against or appearing as a third-party witness in connection with
     any such loss, claim, damage, liability or action; PROVIDED, HOWEVER, that
     neither the Company nor the Subsidiary Guarantors will be liable in any
     such case to the extent that any such loss, claim, damage or liability
     arises out of or is based upon any untrue statement or alleged untrue
     statement or omission or alleged omission made in such registration
     statement or any amendment thereto, any Preliminary Prospectus, the
     Prospectus or any amendment or supplement thereto or any Application in
     reliance upon and in conformity with written information furnished to the
     Company by such Underwriter through the Representatives specifically for
     use therein; and PROVIDED, FURTHER, that the neither Company nor the
     Subsidiary Guarantors will be liable to any Underwriter or any person
     controlling such Underwriter with respect to any such untrue statement or
     omission made in any Preliminary Prospectus that is corrected in the
     Prospectus (or any amendment or supplement thereto) if the person asserting
     any such loss, claim, damage or liability purchased Securities from such
     Underwriter but was not sent or given a copy of the Prospectus (as amended
     or supplemented) at or prior to the written confirmation of the sale of
     such Securities to such person in any case where such delivery of the
     Prospectus (as amended or supplemented) is required by the Act, unless such
     failure to deliver the Prospectus (as amended or supplemented) was a result
     of noncompliance by the Company with Sections 5(b) or 5(d) of this
     Agreement.  This indemnity agreement will be in addition to any liability
     which the Company may otherwise have.  The Company will not, without the
     prior written consent of the Underwriter or Underwriters purchasing, in the
     aggregate, more than fifty percent (50%) of the Securities, settle or
     compromise or consent to the entry of any judgment in any pending or
     threatened claim, action, suit or proceeding in respect of which
     indemnification may be sought hereunder (whether or not any such
     Underwriter or any person who controls any such Underwriter within the
     meaning of Section 15 of the Act or Section 20 of the Exchange Act is a
     party to such claim, action, suit or proceeding), unless such settlement,
     compromise or consent includes an unconditional release of all of the
     Underwriters and such controlling persons from all liability arising out of
     such claim, action, suit or proceeding.

          (b)  Each Underwriter, severally and not jointly, will indemnify and
     hold harmless the Company, each of the Subsidiary Guarantors, each of the
     directors of the Company, each of its officers who signed the Registration
     Statement and each person, if any, who controls the Company within the
     meaning of Section 15 of the Act or Section 20 of the Exchange Act against
     any losses, claims, damages or liabilities to which the Company, such
     Subsidiary Guarantor, or any such director, officer or controlling person
     may become subject under the Act or otherwise, insofar as such losses,
     claims, damages or liabilities (or actions in respect thereof) arise out of
     or are based upon (i) any untrue statement or alleged untrue statement of
     any material fact contained in the Registration Statement or any amendment
     thereto, any Preliminary Prospectus or the Prospectus or any amendment or
     supplement thereto, or any Application or (ii) the omission or the alleged
     omission to state therein a material fact required to be stated in the
     Registration Statement or any amendment thereto, any Preliminary Prospectus
     or the Prospectus or any amendment or supplement thereto, or any

                                     -21- 
<PAGE>

     Application or necessary to make the statements therein not misleading, in
     each case to the extent, but only to the extent, that such untrue statement
     or alleged untrue statement or omission or alleged omission was made in
     reliance upon and in conformity with written information furnished to the
     Company by such Underwriter through the Representatives specifically for
     use therein; and, subject to the limitation set forth immediately preceding
     this clause, will reimburse, as incurred, any legal or other expenses
     reasonably incurred by the Company, such Subsidiary Guarantor, or any such
     director, officer or controlling person in connection with investigating or
     defending any such loss, claim, damage, liability or any action in respect
     thereof.  This indemnity agreement will be in addition to any liability
     which such Underwriter may otherwise have.

          (c)  Promptly after receipt by an indemnified party under this Section
     8 of notice of the commencement of any action, such indemnified party will,
     if a claim in respect thereof is to be made against the indemnifying party
     under this Section 8, notify the indemnifying party of the commencement
     thereof; but the omission so to notify the indemnifying party will not
     relieve it from any liability which it may have to any indemnified party
     otherwise than under this Section 8.  In case any such action is brought
     against any indemnified party, and it notifies the indemnifying party of
     the commencement thereof, the indemnifying party will be entitled to
     participate therein and, to the extent that it may wish, jointly with any
     other indemnifying party similarly notified, to assume the defense thereof,
     with counsel satisfactory to such indemnified party; PROVIDED, HOWEVER,
     that if the defendants in any such action include both the indemnified
     party and the indemnifying party and the indemnified party shall have
     reasonably concluded that there may be one or more legal defenses available
     to it and/or other indemnified parties which are different from or
     additional to those available to the indemnifying party, the indemnifying
     party shall not have the right to direct the defense of such action on
     behalf of such indemnified party or parties and such indemnified party or
     parties shall have the right to select separate counsel to defend such
     action on behalf of such indemnified party or parties.  After notice from
     the indemnifying party to such indemnified party of its election so to
     assume the defense thereof and approval by such indemnified party of
     counsel appointed to defend such action, the indemnifying party will not be
     liable to such indemnified party under this Section 8 for any legal or
     other expenses, other than reasonable costs of investigation, subsequently
     incurred by such indemnified party in connection with the defense thereof,
     unless (i) the indemnified party shall have employed separate counsel in
     accordance with the proviso to the preceding sentence (it being understood,
     however, that in connection with such action the indemnifying party shall
     not be liable for the expenses of more than one separate counsel (in
     addition to local counsel) in any one action or separate but substantially
     similar actions in the same jurisdiction arising out of the same general
     allegations or circumstances, designated by the Representatives in the case
     of paragraph (a) of this Section 8, representing the indemnified parties
     under such paragraph (a) who are parties to such action or actions) or (ii)
     the indemnifying party does not promptly retain counsel satisfactory to the
     indemnified party or (iii) the indemnifying party has authorized the
     employment of counsel for the indemnified party at the expense of the
     indemnifying party.  After such notice from the indemnifying party to such
     indemnified party, the indemnifying party will not be liable for the costs
     and expenses of any settlement 

                                     -22- 
<PAGE>

     of such action effected by such indemnified party without the consent of 
     the indemnifying party.

          (d)  In circumstances in which the indemnity agreement provided for in
     the preceding paragraphs of this Section 8 is unavailable or insufficient,
     for any reason, to hold harmless an indemnified party in respect of any
     losses, claims, damages or liabilities (or actions in respect thereof),
     each indemnifying party, in order to provide for just and equitable
     contribution, shall contribute to the amount paid or payable by such
     indemnified party as a result of such losses claims, damages or liabilities
     (or actions in respect thereof) in such proportion as is appropriate to
     reflect (i) the relative benefits received by the indemnifying party or
     parties on the one hand and the indemnified party or parties on the other
     from the offering of the Securities or (ii) if the allocation provided by
     the foregoing clause (i) is not permitted by applicable law, not only such
     relative benefits but also the relative fault of the indemnifying party or
     parties on the one hand and the indemnified party or parties on the other
     in connection with the statements or omissions or alleged statements or
     omissions that resulted in such losses, claims, damages or liabilities (or
     actions in respect thereof), as well as any other relevant equitable
     considerations.  The relative benefits received by the Company and the
     Subsidiary Guarantors on the one hand and the Underwriters on the other
     shall be deemed to be in the same proportion as the total proceeds from the
     offering (before deducting expenses) received by the Company bear to the
     total underwriting discounts and commissions received by the Underwriters. 
     The relative fault of the parties 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 Company or the Underwriters, the
     parties' relative intents, knowledge, access to information and opportunity
     to correct or prevent such statement or omission, and any other equitable
     considerations appropriate in the circumstances.  The Company and the
     Underwriters agree that it would not be equitable if the amount of such
     contribution were determined by pro rata or per capita allocation (even if
     the Underwriters were treated as one entity for such purpose) or by any
     other method of allocation that does not take into account the equitable
     considerations referred to above in this paragraph (d).  Notwithstanding
     any other provision of this paragraph (d), no Underwriter shall be
     obligated to make contributions hereunder that in the aggregate exceed the
     total public offering price of the Securities purchased by such Underwriter
     under this Agreement, less the aggregate amount of any damages that such
     Underwriter has otherwise been required to pay in respect of the same or
     any substantially similar claim, and no person guilty of fraudulent
     misrepresentation (within the meaning of Section 11(f) of the Act) shall
     be entitled to contribution from any person who was not guilty of such
     fraudulent misrepresentation.  The Underwriters' obligations to contribute
     hereunder are several in proportion to their respective underwriting
     obligations and not joint, and contributions among Underwriters shall be
     governed by the provisions of the Prudential Securities Incorporated Master
     Agreement Among Underwriters.  For purposes of this paragraph (d), each
     person, if any, who controls an Underwriter within the meaning of Section
     15 of the Act or Section 20 of the Exchange Act shall have the same rights
     to contribution as such Underwriter, and each director of the Company, each
     officer of the Company who signed the Registration Statement and each

                                     -23- 
<PAGE>

     person, if any, who controls the Company within the meaning of Section 15
     of the Act or Section 20 of the Exchange Act, shall have the same rights to
     contribution as the Company.

     9.   DEFAULT OF UNDERWRITERS.  If one or more Underwriters default in their
obligations to purchase Firm Securities or Option Securities hereunder and the
aggregate number of such Securities that such defaulting Underwriter or
Underwriters agreed but failed to purchase is ten percent or less of the
aggregate number of Firm Securities or Option Securities to be purchased by all
of the Underwriters at such time hereunder, the other Underwriters may make
arrangement satisfactory to the Representatives for the purchase of such
Securities by other persons (who may include one or more of the non-defaulting
Underwriters, including the Representatives), but if no such arrangements are
made by the Firm Closing Date or the related Option Closing Date, as the case
may be, the other Underwriters shall be obligated severally in proportion to
their respective commitments hereunder to purchase the Firm Securities or Option
Securities that such defaulting Underwriter or Underwriters agreed but failed to
purchase.  If one or more Underwriters so default with respect to an aggregate
number of Securities that is more than ten percent of the aggregate number of
Firm Securities or Option Securities, as the case may be, to be purchased by all
of the Underwriters at such time hereunder, and if arrangements satisfactory to
the Representatives are not made within 36 hours after such default for the
purchase by other persons (who may include one or more of the non-defaulting
Underwriters, including the Representatives) of the Securities with respect to
which such default occurs, this Agreement will terminate without liability on
the part of any non-defaulting Underwriter or the Company other than as provided
in Section 10 hereof.  In the event of any default by one or more Underwriters
as described in this Section 9, the Representatives shall have the right to
postpone the Firm Closing Date or the Option Closing Date as the case may be,
established as provided in Section 3 hereof for not more than seven business
days in order that any necessary changes may be made in the arrangements or
documents for the purchase and delivery of the Firm Securities or Option
Securities, as the case may be.  As used in this Agreement, the term
"Underwriter" includes any person substituted for an Underwriter under this
Section 9.  Nothing herein shall relieve any defaulting Underwriter from
liability for it default.

     10.  SURVIVAL.  The respective representations, warranties, agreements,
covenants, indemnities and other statements of the Company, its officers and the
several Underwriters set forth in this Agreement or made by or on behalf of
them, respectively, pursuant to this Agreement shall remain in full force and
effect, regardless of (i) any investigation made by or on behalf of the Company,
any of its officers or directors, any Underwriter or any controlling person
referred to in Section 8 hereof and (ii) delivery of and payment for the
Securities.  The respective agreements, covenants, indemnities and other
statements set forth in Sections 6 and 8 hereof shall remain in full force and
effect, regardless of any termination or cancellation of this Agreement.

     11.  TERMINATION.  (a) This Agreement may be terminated with respect to the
     Firm Securities or any Option Securities in the sole discretion of the
     Representatives by notice to the Company given prior to the Firm Closing
     Date or the related Option Closing Date, respectively, in the event that
     the Company shall have failed, refused or been unable to perform all
     obligations and satisfy all conditions on its part to be performed or
     satisfied hereunder at or prior thereto or, if at or prior to the Firm
     Closing Date or such Option Closing Date, respectively,

                                     -24- 
<PAGE>

               (i)    the Company or any of its subsidiaries shall have, in the
          sole judgment of the Representatives, sustained any material lose or
          interference with their respective businesses or properties from fire,
          flood, hurricane, accident or other calamity, whether or not covered
          by insurance, or from any labor dispute or any legal or governmental
          proceeding or there shall have been any material adverse change, or
          any development involving a prospective material adverse change
          (including without limitation a change in management or control of the
          Company), in the condition (financial or otherwise), business
          prospects, net worth or results of operations of the Company and its
          subsidiaries, except in each case as described in or contemplated by
          the Prospectus (exclusive of any amendment or supplement thereto);

               (ii)   trading in the Common Stock shall have been suspended by 
          the Commission or the Nasdaq National Market or trading in securities
          generally on the New York Stock Exchange or Nasdaq National Market
          shall have been suspended or minimum or maximum prices shall have been
          established on either such exchange or market system;

               (iii)  a banking moratorium shall have been declared by New York
          or United States authorities; or

               (iv)   there shall have been (A) an outbreak or escalation of
          hostilities between the United States and any foreign power, (B) an
          outbreak or escalation of any other insurrection or armed conflict
          involving the United States or (C) any other calamity or crisis or
          material adverse change in general economic, political or financial
          conditions having an effect on the U.S. financial markets that, in the
          sole judgment of the Representatives, makes it impractical or
          inadvisable to proceed with the public offering or the delivery of the
          Securities as contemplated by the Registration Statement, as amended
          as of the date hereof.

          (b)  Termination of this Agreement pursuant to this Section 11 shall
     be without liability of any party to any other party except as provided in
     Section 10 hereof.

     12.  INFORMATION SUPPLIED BY UNDERWRITERS.  The statements set forth in 
the last paragraph on the front cover page and under the heading 
"Underwriting" in any Preliminary Prospectus or the Prospectus (to the extent 
such statements relate to the Underwriters) constitute the only information 
furnished by any Underwriter through the Representatives to the Company for 
the purposes of Sections 2(b) and 8 hereof.  The Underwriters confirm that 
such statements (to such extent) are correct.

     13.  NOTICES.  All communications hereunder shall be in writing and, if 
sent to any of the Underwriters, shall be delivered or sent by mail, telex or 
facsimile transmission and confirmed in writing to Prudential Securities 
Incorporated, One New York Plaza, New York, New York 10292, Attention: Equity 
Transactions Group; and if sent to the Company, shall be delivered or sent by 
mail, telex or facsimile transmission and confirmed in writing to the Company 
at Costilla Energy, Inc., 

                                     -25- 
<PAGE>

400 West Illinois, Suite 1000, Midland, Texas  79701, to the attention of the 
Secretary with copy to the President.

     14.  SUCCESSORS.  This Agreement shall inure to the benefit of and shall 
be binding upon the several Underwriters, the Company and their respective 
successors and legal representatives, and nothing expressed or mentioned in 
this Agreement is intended or shall be construed to give any other person any 
legal or equitable right, remedy or claim under or in respect of this 
Agreement, or any provisions herein contained, this Agreement and all 
conditions and provisions hereof being intended to be and being for the sole 
and exclusive benefit of such persons and for the benefit of no other person 
except that (i) the indemnities of the Company and the Subsidiary Guarantors 
contained in Section 8 of this Agreement shall also be for the benefit of any 
person or persons who control any Underwriter within the meaning of Section 
15 of the Act or Section 20 of the Exchange Act and (ii) the indemnities of 
the Underwriters contained in Section 8 of this Agreement shall also be for 
the benefit of the directors of the Company, the officers of the Company who 
have signed the Registration Statement and any person or persons who control 
the Company within the meaning of Section 15 of the Act or Section 20 of the 
Exchange Act.  No purchaser of Securities from an Underwriter shall be deemed 
a successor because of such purchase.

     15.  APPLICABLE LAW.  The validity and interpretation of this Agreement, 
and the term and conditions set forth herein, shall be governed by and 
construed in accordance with the law of the State of New York, without giving 
effect to any provisions relating to conflicts of laws.

     16.  COUNTERPARTS.  This Agreement may be executed in two or more 
counterparts, each of which shall be deemed an original, but all of which 
together shall constitute one and the same instrument.



















                                     -26- 
<PAGE>

     If the foregoing correctly sets forth our understanding, please indicate 
your acceptance thereof in the space provided below for that purpose, 
whereupon this letter shall constitute an agreement binding the Company and 
each of the several Underwriters.

                                      Very truly yours,

                                      COSTILLA ENERGY, INC.



                                      By:       
                                         ------------------------------------ 
                                         Name:  
                                         Title: 

                                      [SUBSIDIARY GUARANTORS]


                                      By:       
                                         ------------------------------------ 
                                         Name:  
                                         Title: 


The foregoing Agreement is hereby
confirmed and accepted as of the
date first above written.

PRUDENTIAL SECURITIES INCORPORATED
RAUSCHER PIERCE REFSNES, INC.

By PRUDENTIAL SECURITIES INCORPORATED


By:       
   ------------------------------------ 
   Name:  
   Title: 

For itself and on behalf of the Representatives.





                                    -27- 
<PAGE>


                                SCHEDULE 1  

                               UNDERWRITERS 


                                                 NUMBER OF FIRM 
                                                  SECURITIES TO 
UNDERWRITER                                       BE PURCHASED  
- -----------                                      -------------- 
Prudential Securities Incorporated............  

Rauscher Pierce Refsnes, Inc. ................  

               Total..........................   -------------- 
























                                     -28- 


<PAGE>
                                                                    EXHIBIT 23.1
 
                        CONSENT OF INDEPENDENT AUDITORS
 
The Members
Costilla Energy, L.L.C.
 
    We consent to the use of our reports included herein and to the reference to
our firm under the heading "Experts" in the Prospectus.
 
                                          KPMG PEAT MARWICK LLP
 
Midland, Texas
July 26, 1996

<PAGE>
                                                                    EXHIBIT 23.2
 
                        CONSENT OF INDEPENDENT ENGINEERS
 
    As  independent engineering consultants, we hereby consent to the use of our
Summary Reserve Report entitled "Summary  Letter (for Inclusion in a  Prospectus
Included  in a  Registration Statement  for Costilla  Energy, Inc.  on Form S-1)
Combining  Specific  Data  from  Two  Williamson  Petroleum  Consultants,   Inc.
Evaluations  (1) to the  Interests of Costilla  Petroleum Corporation in Various
Properties and (2) to the Interests of  Parker & Parsley Petroleum USA, Inc.  in
Various Properties Included in Their First Quarter 1996 Sales Package, Effective
April  1,  1996, Williamson  Project 6.8393"  dated July  23, 1996  prepared for
Costilla Energy, Inc., and data extracted  therefrom (and all references to  our
Firm,  including any  references as  Experts) included  in or  made part  of the
Prospectus included in this Registration Statement on Form S-1.
 
                                     WILLIAMSON PETROLEUM CONSULTANTS, INC.
 
Houston, Texas
July 23, 1996

<PAGE>
                                                                    EXHIBIT 23.3
 
                        CONSENT OF INDEPENDENT AUDITORS
 
The Members
Costilla Energy, L.L.C.
 
    We consent to the use of our reports included herein and to the reference to
our firm under the heading "Experts" in the Prospectus.
 
                                          ELMS, FARIS & CO., P.C.
 
Midland, Texas
July 26, 1996

<PAGE>
                                                              EXHIBIT 24.1 

                                POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS, the undersigned, being certain of the 
Officers and all of the Directors of Costilla Energy, Inc., a Delaware 
Corporation, do hereby constitute and appoint Michael J. Grella and Bobby W. 
Page, or either of them, with full power of substitution, our true and lawful 
attorneys and agents, to do any and all acts and things in our names in the 
capacities indicated which Michael J. Grella and Bobby W. Page, or either of 
them, may deem necessary or advisable to enable the Company to comply with 
the Securities Act of 1933, as amended, any state securities laws and any 
rules, regulations and requirements of the Securities and Exchange Commission 
in connection with the Registration Statement seeking to register shares of 
Common Stock, $.10 par value, of Costilla Energy, Inc., including 
specifically, but not limited to, the power and authority to sign such 
Registration Statement, any and all amendments (including post-effective 
amendments) to such Registration Statement and any other forms or documents 
related to such Registration Statement which are required under federal or 
state securities laws for us, or any of us, in our names in the capacities 
indicated; and we do hereby ratify and confirm all that Michael J. Grella and 
Bobby W. Page, or either of them, shall do or cause to be done by virtue 
hereof.  This Power of Attorney may be signed in any number of counterparts, 
and each such counterpart shall be considered an original hereof.

     IN WITNESS WHEREOF I have hereunto set my hand this 12th day of July, 
1996.

                              /s/  Cadell S. Liedtke                         
                              ---------------------------------------------- 
                              CADELL S. LIEDTKE, Chairman of the Board,
                              Chief Executive Officer and Director


                              /s/  Michael J. Grella                         
                              ---------------------------------------------- 
                              MICHAEL J. GRELLA, President, Chief
                              Operating Officer and Director


                              /s/  Henry G. Musselman                        
                              ---------------------------------------------- 
                              HENRY G. MUSSELMAN, Executive Vice
                              President and Director


                              /s/  Bobby W. Page                             
                              ---------------------------------------------- 
                              BOBBY W. PAGE, Senior Vice President,
                              Treasurer and Chief Financial Officer


                              /s/  Jerry Langdon                             
                              ---------------------------------------------- 
                              JERRY LANGDON, Director


                              /s/  W. D. Kennedy                             
                              ---------------------------------------------- 
                              W. D. KENNEDY, Director




<PAGE>
                                                           EXHIBIT 24.2 

                    CERTIFICATE OF RESOLUTION



     I, CLIFFORD N. HAIR, JR., Secretary of Costilla Energy, Inc., a Delaware 
corporation, do hereby certify that the Board of Directors of Costilla 
Energy, Inc., acting by unanimous written consent, duly adopted the following 
resolutions as of July 1, 1996:

          RESOLVED, that the directors and officers of the Corporation 
     are hereby authorized and directed to execute and deliver a Power 
     of Attorney to Michael J. Grella and Bobby W. Page in the following
     form:

               KNOW ALL MEN BY THESE PRESENTS, the undersigned, being 
     certain of the Officers and all of the Directors of Costilla Energy,
     Inc., a Delaware Corporation, do hereby constitute and appoint 
     MICHAEL J. GRELLA and BOBBY W. PAGE, or either of them, with fully 
     power of substitution, our true and lawful attorneys and agents, to 
     do any and all acts and things in our names and in the capacities 
     indicated which MICHAEL J. GRELLA and BOBBY W. PAGE, or either of 
     them, may deem necessary or advisable to enable the Company to comply 
     with the Securities Act of 1933, as amended, any state securities 
     laws, and any rules, regulations, and requirements of the Securities
     and Exchange Commission in connection with the Registration Statement
     seeking to register shares of Common Stock, $.10 par value of Costilla
     Energy, Inc., including specifically, but not limited to, the power and
     authority to sign such Registration Statement, any and all amendments
     (including post-effective amendments) to such Registration Statement, 
     and any other forms or documents related to such Registration Statement
     which are required under federal or state securities laws for us, or any
     of us, in our names in the capacities indicated; and we do hereby ratify
     and confirm all that MICHAEL J. GRELLA and BOBBY W. PAGE, or either of 
     them, shall do or cause to be done by virtue hereof.  This Power of 
     Attorney may be signed in any number of counterparts, and each such 
     counterpart shall be considered an original hereof.

          RESOLVED, that the Officers of the Corporation are hereby authorized
     and directed to take all such further action as they may deem advisable 
     in order to carry out the intent and purposes of the foregoing 
     resolutions.


     IN WITNESS WHEREOF, I have hereunto set my hand on behalf of this 
Corporation on this 15th day of July, 1996.

                                  /s/  Clifford N. Hair, Jr.      
                              ----------------------------------- 
                              CLIFFORD N. HAIR, JR., Secretary    


<TABLE> <S> <C>

<PAGE>
<ARTICLE> 5
<LEGEND>
THE SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM THE FINANCIAL
STATEMENTS OF COSTILLA ENERGY, L.L.C. FOR YEARS ENDED DECEMBER 31, 1993, 1994
AND 1995 AND THE UNAUDITED PERIODS MARCH 31, 1995 AND 1996, AND IS QUALIFIED IN
ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
       
<S>                             <C>                     <C>
<PERIOD-TYPE>                   YEAR                   3-MOS
<FISCAL-YEAR-END>                          DEC-31-1995             DEC-31-1996
<PERIOD-START>                             JAN-01-1995             JAN-01-1996
<PERIOD-END>                               DEC-31-1995             MAR-31-1996
<CASH>                                           2,616                   2,760
<SECURITIES>                                         0                       0
<RECEIVABLES>                                    7,576                   7,584
<ALLOWANCES>                                         0                       0
<INVENTORY>                                          0                       0
<CURRENT-ASSETS>                                10,881                  11,394
<PP&E>                                          83,479                  88,569
<DEPRECIATION>                                 (9,413)                (11,281)
<TOTAL-ASSETS>                                  87,367                  91,024
<CURRENT-LIABILITIES>                            8,385                   9,290
<BONDS>                                         71,494                  74,494
                           11,320                  11,678
                                          0                       0
<COMMON>                                             0                       0
<OTHER-SE>                                     (7,189)                 (7,535)
<TOTAL-LIABILITY-AND-EQUITY>                    87,367                  91,024
<SALES>                                         21,693                   8,833
<TOTAL-REVENUES>                                21,816                   8,951
<CGS>                                           10,355                   3,659
<TOTAL-COSTS>                                   12,005                   3,887
<OTHER-EXPENSES>                                 6,097                   1,986
<LOSS-PROVISION>                                     0                       0
<INTEREST-EXPENSE>                               4,454                   1,704
<INCOME-PRETAX>                                (4,311)                      12
<INCOME-TAX>                                         3                       0
<INCOME-CONTINUING>                            (4,314)                      12
<DISCONTINUED>                                       0                       0
<EXTRAORDINARY>                                      0                       0
<CHANGES>                                            0                       0
<NET-INCOME>                                   (4,314)                      12
<EPS-PRIMARY>                                        0                       0
<EPS-DILUTED>                                        0                       0
        

</TABLE>


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