MESA INC
8-K, 1997-08-22
CRUDE PETROLEUM & NATURAL GAS
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                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549



                                    FORM 8-K

                                 CURRENT REPORT


     Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

        Date of Report (Date of earliest event reported): August 7, 1997



                                    MESA INC.
             (Exact name of Registrant as specified in its charter)




                Texas                     1-10874              75-2394500
    (State or other jurisdiction of      Commission         (I.R.S. Employer
    incorporation or organization)       File Number     Identification Number)




1400 Williams Square West, 5205 N. O'Connor Blvd. Irving, Texas     75039
          (Address of principal executive offices)                (Zip code)



       Registrant's Telephone Number, including area code : (972) 444-9001


                                 Not applicable
              (Former name, former address and former fiscal year,
                          if changed since last report)




                               Page 1 of 26 pages.

                            Exhibit Index on page 26.



<PAGE>



                                    MESA INC.

                                TABLE OF CONTENTS


                                                                           Page
                                                                           ----
Item 1.  Change in Control of Registrant..................................    3

Item 2.  Acquisition or Disposition of Assets.............................    3

Item 7.  Financial Statements and Exhibits:...............................   10

           Preliminary Statement..........................................   10

           Unaudited Pro Forma Combined Financial Statements:

             Unaudited Pro Forma Combined Balance Sheet for Pioneer
                Natural Resources Company as of June 30, 1997.............   11
             Unaudited Pro Forma Combined Statement of Operations for
                Pioneer Natural Resources Company for the six months
                ended June 30, 1997.......................................   12
             Unaudited Pro Forma Combined Statement of Operations for
                Pioneer Natural Resources Company for the year ended
                December 31, 1996.........................................   13
             Unaudited Pro Forma Combined Statement of Operations for
                Parker & Parsley Petroleum Company for the year ended
                December 31, 1996.........................................   14
             Unaudited Pro Forma Combined Statement of Operations for
                Mesa Inc. for the year ended December 31, 1996............   15

           Notes to Unaudited Pro Forma Combined Financial Statements.....   16

           Exhibits.......................................................   24

           Signatures.....................................................   25

           Exhibit Index..................................................   26



                                        2

<PAGE>


The information in this document  includes  forward-looking  statements that are
based on  assumptions  that in the future  may prove not to have been  accurate.
Those  statements,   and  Pioneer  Natural  Resources   Company's  business  and
prospects,  are subject to a number of risks including the volatility of oil and
gas prices,  environmental risks,  operating hazards and risks, risks associated
with natural gas processing plants, risks related to exploration and development
drilling,  uncertainties  about estimates of reserves,  competition,  government
regulation,  and the ability of Pioneer Natural  Resources  Company to implement
its business  strategy.  These and other risks are  described in the 1996 Annual
Reports on Form 10-K for Parker & Parsley  Petroleum Company and Mesa Inc. which
are available from the United States Securities and Exchange Commission.

Item 1.      Changes in Control of Registrant

       Pioneer Natural Resources Company  ("Pioneer"),  a Delaware  corporation,
was formed in order to complete  the merger  proposed  by and  between  Parker &
Parsley Petroleum Company ("Parker & Parsley") and Mesa Inc.  ("Mesa").  Pioneer
was  originally   created  as  a  wholly-owned   subsidiary  of  Mesa,  a  Texas
corporation,  the  purpose  of which was to allow Mesa to  reincorporate  into a
Delaware  corporation  and to accomplish the merger with Parker & Parsley.  Both
Parker & Parsley and Mesa are oil and gas  exploration  and production  concerns
with ownership  interests in oil and gas properties  located  principally in the
MidContinent,  Southwestern  and onshore and offshore  Gulf Coast regions of the
United States, and with limited international interests.

       As a  result  of  the  Mergers  described  in  "Item  2.  Acquisition  or
Disposition of Assets", Mesa Inc. ("Mesa") merged into Pioneer Natural Resources
Company  ("Pioneer").  Former  Parker & Parsley  Petroleum  Company  ("Parker  &
Parsley") stockholders received approximately 57% of the common stock of Pioneer
and former Mesa stockholders  received  approximately 43% of the common stock of
Pioneer.  In some  circumstances,  this transaction could be deemed a "change in
control of a registrant". For a more complete description of these transactions,
see "Item 2. Acquisition or Disposition of Assets" below.

Item 2.      Acquisition or Disposition of Assets

       As of April 6, 1997,  Parker & Parsley and Mesa  entered  into an Amended
and Restated  Agreement  and Plan of Merger (the "Merger  Agreement")  which was
approved by the  stockholders  of both companies on August 7, 1997 by a majority
vote of 76% by holders of Parker & Parsley  common stock and 71%,  58%, and 100%
by  holders  of Mesa  common  stock,  Mesa  Series A 8%  Cumulative  Convertible
Preferred  Stock  ("Mesa  Series  A  Preferred  Stock")  and  Mesa  Series  B 8%
Cumulative  Convertible  Preferred  Stock  ("Mesa  Series B  Preferred  Stock"),
respectively.  Parker & Parsley was a publicly  traded  independent  oil and gas
company  based in  Midland,  Texas with  substantial  producing  properties  and
operations  in the Permian Basin of West Texas and the onshore Gulf Coast region
of the United States.  The Merger Agreement  provided for (i) the merger of Mesa
with and into Pioneer,  a wholly-owned  subsidiary of Mesa, as a result of which
Mesa, a Texas corporation,  reincorporated  into Delaware and (ii) the merger of
Parker & Parsley  with and into  Mesa  Operating  Co.  ("MOC"),  a  wholly-owned
subsidiary  of  Mesa  (items  (i)  and  (ii)  collectively  the  "Mergers").  In
accordance  with the Merger  Agreement,  (i) holders of Parker & Parsley  common
stock  received  one share of Pioneer  common  stock for each share  held;  (ii)
holders of Mesa common  stock  received  one share of Pioneer  common  stock for
every seven shares held; and (iii) holders of Mesa Series A Preferred  Stock and
Mesa Series B Preferred  Stock  received 1.25 shares of Pioneer common stock for
every seven  shares  held.  No  fractional  shares were issued and all  treasury
shares were canceled.

       As a result of the Mergers, former Parker & Parsley stockholders received
approximately  57% of the common stock of Pioneer,  and former Mesa stockholders
received  approximately 43%. Also, as a result of the Mergers,  Mesa merged into
Pioneer and Parker & Parsley  merged into a  wholly-owned  subsidiary of Pioneer
that is now  known  as  Pioneer  Natural  Resources  USA,  Inc.  For a  complete
description of the Mergers and of Pioneer, see Pioneer's  Registration Statement
on Form S-4 (File No. 333-26951) which is incorporated herein by reference.

       In accordance with the provisions of Accounting  Principles Board No. 16,
"Business Combinations", the merger has been accounted for as a purchase of Mesa
by Parker & Parsley. As a result,  historical  financial  statements for Pioneer
will be those of Parker &  Parsley,  and  Pioneer's  financial  statements  will
present the  addition of Mesa's  assets and  liabilities  as an  acquisition  by

                                        3

<PAGE>



Parker & Parsley.  The aggregate Pioneer purchase  consideration  related to the
assets  and  liabilities  of  Mesa,  including  estimated   nonrecurring  merger
transaction  costs,  is $999.5  million.  See "Item 7. Financial  Statements and
Exhibits" for the preliminary  allocation of the total purchase price of Mesa to
the  acquired  assets and  liabilities  based  upon the  estimated  fair  values
assigned to each of the significant assets acquired and liabilities assumed. Any
future  adjustments to the allocation of the purchase price are not  anticipated
to be material to Pioneer's financial statements.

Description of Properties

       Approximately  95% of Mesa's estimated proved reserves as of December 31,
1996 were  concentrated  in the Hugoton  field of southwest  Kansas and the West
Panhandle field of Texas.  These fields,  which produce gas from depths of 3,500
feet or less, are characterized by stable,  long-lived,  low cost production. On
the other hand, Mesa's Gulf of Mexico  properties  contained less than 3% of the
total estimated proved reserves as of December 31, 1996.

       Oil and Gas Properties

       Hugoton  Field.  The  Hugoton  field in  southwest  Kansas  is one of the
largest  producing gas fields in the continental  United States.  Mesa's Hugoton
properties  represent  approximately 13% of the proved reserves in the field and
are located on over 237,000 net acres, covering  approximately 400 square miles.
Mesa's  properties  are  concentrated  in the  central  fairway of the field and
benefit from better  reservoir  characteristics,  including  thicker  productive
zones,  higher porosity and higher  permeability than properties on the edges of
the field.  Mesa has  working  interests  in  approximately  1,100  wells in the
Hugoton field, 950 of which it operates,  and royalty interests in approximately
800 wells. Mesa's Hugoton properties are capable of producing  approximately 200
MMcf of gas per  day and  substantially  all of  Mesa's  Hugoton  production  is
processed through its Satanta plant. Mesa's gathering and processing  facilities
which service its  production  from the Hugoton field allows Mesa to control the
production, gathering, processing and sale of its gas and associated natural gas
liquids to various major intrastate and interstate  pipelines through its direct
interconnects.

       Mesa's Hugoton  properties  accounted for approximately 60% of its proved
reserves  and 62% of the  SEC 10  value  of  estimated  future  net  cash  flows
determined  as of December 31, 1996,  in  accordance  with SEC  guidelines.  The
Hugoton  properties  accounted for approximately  49%, 47% and 53% of Mesa's oil
and gas  revenues  for the  years  ended  December  31,  1996,  1995  and  1994,
respectively.  The  percentage  of revenues from the Hugoton field has been less
than the  percentage of proved  reserves due primarily to the longer life of the
Hugoton properties compared to Mesa's other properties.

        Production  in the  Hugoton  field is subject to  allowables  set by the
Kansas Corporation  Commission (the "KCC"), which is the state regulatory agency
that regulates oil and gas production in Kansas.  The KCC is responsible for the
determination  of  market  demand  (allowables)  for the  Hugoton  field and the
allocation  of  allowables  among the more than 9,000 wells in the field.  Twice
each year, the KCC sets the field wide allowable production at a level estimated
to be  necessary  to meet the  Hugoton  market  demand for the summer and winter
production periods.  The field wide allowable is then allocated among individual
wells determined by a series of calculations  that are principally based on each
well's  pressure,   deliverability  and  acreage.  The  allowables  assigned  to
individual wells are affected by the relative  production,  testing and drilling
practices of all  producers in the field,  as well as the relative  pressure and
deliverability performance of each well.

       Generally,  field wide  allowables  are  influenced by overall gas market
supply and demand in the United States as well as specific  nominations  for gas
from the parties who produce or purchase gas from the field.  Since 1987,  field
wide allowables have increased in each year except 1991. The total Hugoton field
allowable  in 1996  was 600 Bcf of  wellhead  gas.  Mesa's  share  of the  field
allowable averaged 13% in 1996. Mesa estimates that it and other major producers
in the Hugoton field  produced at or near full capacity in 1996 and expects such
practice  to  continue.   Mesa's  net  Hugoton  field  production  decreased  to
approximately  67 Bcfe  in 1996  compared  with 70 Bcfe in 1995 as a  result  of
equipment  maintenance in 1996.  Mesa expects its Hugoton field  production will
decline  slightly  from 1996 levels each year through  1998.  Beginning in 1999,
Mesa expects annual production declines due to normal depletion.

                                        4

<PAGE>



       Mesa has invested over $78 million in capital expenditures in its Hugoton
properties since 1992 to construct the Satanta Plant and related facilities, and
to upgrade  gathering  and  compression  facilities,  production  equipment  and
pipeline  interconnects in order to maintain  production  capacity and marketing
flexibility.  See "Gas  Processing  Facilities - Satanta  Natural Gas Processing
Plant" below.

       West Panhandle  Field.  The West Panhandle  properties are located in the
Texas   panhandle.   Natural  gas  from  these   properties   is  produced  from
approximately 600 wells, all of which Mesa operates,  on over 185,000 net acres.
All of Mesa's West Panhandle production is processed through Mesa's Fain natural
gas processing plant.

       Mesa's  West  Panhandle  reserves  are owned  and  produced  pursuant  to
contracts with Colorado  Interstate Gas Company ("CIG"),  the first of which was
executed  in 1928 by  predecessors  of both  companies.  An  amendment  to these
contracts,  the Production  Allocation  Agreement ("PAA"),  allocates 77% of the
production  from the West  Panhandle  field  properties  to Mesa and 23% to CIG,
effective as of January 1, 1991. Under the associated agreements,  Mesa operates
the wells and  production  equipment  and CIG owns and  operates  the  gathering
system by which Mesa and CIG's  production  is delivered to the Fain Plant.  CIG
also performs certain administrative  functions. Each party reimburses the other
for certain  costs and expenses  incurred for the joint  account.  In accordance
with the PAA and other  contracts  with CIG, Mesa was  contractually  limited to
take  wellhead gas  production  up to a maximum of 32 Bcf in 1996,  but actually
took only 27 Bcf primarily due to a weather related  decrease in demand in 1996.
Beginning  in  1997,  Mesa  is not  subject  to  annual  contractual  production
limitations  and will  have the  right to take and  market as much gas as it can
produce, subject to specific CIG seasonal and daily entitlements as provided for
under the contracts.  Assuming  continuation of existing  economic and operating
conditions,  Mesa expects wellhead production from its West Panhandle properties
to be 37 Bcf in 1997.

       As of December 31, 1996,  Mesa's West  Panhandle  properties  represented
approximately 35% of Mesa's equivalent proved reserves, and approximately 33% of
the present value of estimated  future net cash flows,  determined in accordance
with SEC guidelines. Production from the West Panhandle properties accounted for
approximately  31%,  33% and 36% of Mesa's  oil and gas  revenues  for the years
ended December 31, 1996, 1995 and 1994,  respectively.  Mesa has identified over
100 locations that have additional  production  potential in new areas or deeper
zones, of which Mesa plans to redrill 58 in 1997 and the balance in 1998.

       In December 1996,  Mesa entered into a natural gas  processing  agreement
with CIG and MAPCO,  Inc.  ("MAPCO"),  which has a primary term through December
2009. This agreement  provides for Mesa to initially  process  approximately 8.5
Bcf of  natural  gas per year of third  party  gas at the Fain  Plant  (see "Gas
Processing  Facilities - Fain Natural Gas Processing  Plant" below). In February
1997,  Mesa  purchased  from  MAPCO  and its  affiliates  all of  their  liquids
attributable  to the  processing  agreement  above  as  well  as the  rights  to
condensate  from CIG's  gathering  system for  approximately  $66  million.  The
reserves  associated with this  acquisition are estimated to be 11 million BOE's
at December 31, 1996 and 1997  condensate  and NGL production is estimated to be
850 MBbls.

       Gulf of Mexico.  Mesa's Gulf of Mexico properties are located in offshore
Texas and Louisiana and represent  approximately 3% of Mesa's  equivalent proved
reserves and  approximately 4% of the present value of estimated future net cash
flows as determined in accordance  with SEC guidelines at December 31, 1996. The
Gulf of Mexico properties  accounted for approximately 20%, 13% and 9% of Mesa's
oil and gas  revenues  for the years ended  December  31,  1996,  1995 and 1994,
respectively.

       Mesa has owned and operated  properties in the Gulf of Mexico since 1970.
Beginning  in late 1994,  Mesa began to direct a greater  portion of its capital
spending towards  exploration and development in the Gulf of Mexico.  Since that
time,  Mesa has  successfully  completed  21 out of 24 wells  adding  63 Bcfe to
proved  reserves.   As  a  result,   Mesa's  offshore  production  increased  by
approximately  50% on a thousand cubic feet of natural gas  equivalent  ("Mcfe")
basis from 1994 to 1995,  and by an additional 58% on an Mcfe basis from 1995 to
1996.  Mesa  currently  plans  to drill  up to  seven  exploratory  wells on its
existing  properties  in the  remainder  of  1997.  Because  Mesa  has  existing
production  facilities  offshore,  it has  been  able  to  bring  new  wells  on

                                        5

<PAGE>



production  quickly and at a lower cost than could be achieved  otherwise.  Mesa
currently  owns  interests  in 56 blocks in the Gulf of Mexico,  which  cover an
aggregate of approximately 141,000 net acres.

       Mesa owns  approximately  600  square  miles of 3-D  seismic  data in and
around  its  existing  Gulf of  Mexico  properties.  After  the  procurement  of
additional  3-D  seismic  data  during  1997,  Mesa will have 3-D  seismic  data
covering   approximately  90%  of  its  existing  Gulf  of  Mexico   properties.
Application  of  3-D  seismic  technology  to  Mesa's  Gulf  of  Mexico  acreage
represents a significant  future  opportunity to increase reserves and cash flow
through exploratory and development drilling.

       In 1996,  Mesa  purchased 11 blocks  covering  57,340 gross  (39,685 net)
acres in the Gulf of  Mexico.  Mesa  paid $1.7  million  for its share of the 11
blocks,  six of which are located in areas where Mesa has  producing  interests.
Mesa was apparent high bidder on four blocks  covering 17,500 acres in the March
1997  federal  lease sale in the Gulf of Mexico,  but there can be no  assurance
that Mesa will be awarded these blocks by the United States  Mineral  Management
Service ("MMS"). Mesa will spend approximately $.7 million if the MMS awards all
four leases to Mesa.

       Greenhill Petroleum. On April 15, 1997, Mesa completed the acquisition of
Greenhill  Petroleum  ("Greenhill")  from Western Mining  Corporation  (USA) for
approximately  $267 million,  net of cash  acquired.  At December 31, 1996,  the
Greenhill  properties had estimated  proved reserves of 30 MMBOE  (consisting of
41.9  Bcf of gas and  23.4  MMBbls  of  oil),  which  were  concentrated  in the
following four producing  areas:  the inland waters of the Louisiana Gulf Coast,
the Texas Gulf Coast,  offshore in the Gulf of Mexico and the Permian Basin. The
acquired  properties  included 522 producing  wells,  more than 200  development
projects  and 246  square  miles of 3-D  seismic  data.  During  the year  ended
December 31, 1996,  production from the Greenhill  properties  totaled 6 Bcf and
2.5 MMBbls.

       Gas Processing Facilities

       Through its natural gas  processing  plants,  Mesa  extracts raw NGLs and
crude helium from the wellhead natural gas stream. The NGLs are then transported
and fractionated  into their constituent  hydrocarbons such as ethane,  propane,
normal  butane,  isobutane and natural  gasolines.  The NGLs and helium are then
sold pursuant to contracts providing for market-based prices.

       Mesa  processes its natural gas production for the extraction of NGLs and
helium to enhance the market  value of the gas stream.  In recent years Mesa has
made substantial  capital  investments to enhance its natural gas processing and
helium extraction  capabilities in the Hugoton and West Panhandle  fields.  Mesa
owns and operates its  processing  facilities,  which allows Mesa to (i) capture
the processing margin, as third-party  processing agreements generally available
in the industry  result in retention of a significant  portion of the processing
margin by the  contract  processor,  (ii) control the quality of the residue gas
stream,  permitting  it to deliver gas directly to pipelines  for sales to local
distribution  companies,  marketing  companies and end users,  and (iii) realize
value from premium products such as crude helium. Mesa believes that the ability
to control its  production  stream  from the  wellhead  through  its  processing
facilities to  disposition  at central  delivery  points  enhances its marketing
opportunities and competitive position in the industry.

       Satanta Natural Gas Processing Plant. The Satanta Plant was built in 1993
and has the capacity to process 250 MMcf of natural gas per day,  enabling  Mesa
to extract  NGLs from  substantially  all of the gas  produced  from its Hugoton
field  properties as well as third party  producers' gas. The Satanta Plant also
has the  ability to extract  helium from the gas  stream.  In 1996,  the Satanta
Plant  averaged  193 MMcf per day of inlet gas and  produced a daily  average of
10.6 MBbls of NGLs,  1,027 Mcf of crude  helium and 144 MMcf of residue  natural
gas.

       In November 1996,  Mesa commenced a natural gas processing  alliance with
Anadarko Petroleum Corporation  ("Anadarko") and Western Resources Mid-Continent
Market  Center  which  provides  for  Mesa to  process  up to 55 MMcf per day of
Anadarko's gas at Mesa's Satanta Plant. Such agreement filled excess capacity at
the Satanta  Plant.  Mesa is also  focusing its efforts on obtaining  additional
dedications of third-party  natural gas to the Satanta Plant, and if successful,
plans to expand the plant's processing capacity.

                                       6


<PAGE>



       Fain Natural Gas Processing Plant. The Fain Plant, which was built in the
1960's and had its most recent substantial upgrade in 1993,  currently has inlet
capacity of 140 MMcf per day. In 1996,  the Fain Plant  averaged 77 MMcf per day
of inlet gas and produced a daily  average of 8.2 MMbls of NGLs and  condensate,
20 Mcf of crude helium and 59 MMcf of residue  natural gas.  Mesa's  natural gas
processing agreement with CIG and MAPCO (as described in "Oil and Gas Properties
- - West  Panhandle  Field" above) has filled  excess  capacity at the Fain Plant.
Mesa  plans to install a  nitrogen  rejection  unit at the Fain Plant in 1998 to
improve  the  quality of the residue  natural  gas stream and  increase  NGL and
helium recoveries.

Oil and Gas Information

       Proved Reserves.  The following table sets forth information about Mesa's
proved oil and gas reserves as of December 31, 1996.

                                 PROVED RESERVES
                             As of December 31, 1996

                                    Natural Gas       Oil &        Natural Gas
                    Natural Gas       Liquids       Condensate     Equivalents
                      (MMcf)          (MBbls)        (MBbls)         (MMcfe)
                    -----------     -----------     ----------     -----------
Hugoton                 691,412          45,418            -           963,920
West Panhandle          288,444          42,498          3,971         567,258
Gulf of Mexico           27,332             120          2,188          41,180
Other                    30,534              15            704          34,848
                    -----------    ------------    -----------    ------------
      Total           1,037,722          88,051          6,863       1,607,206
                    ===========    ============    ===========    ============

       Production.   The  following  table  sets  forth  information  about  the
production  attributable to  Mesa's properties  for the year  ended December 31,
1996.
                             OIL AND GAS PRODUCTION
                          Year ended December 31, 1996

                                                Natural Gas         Oil &
                              Natural Gas         Liquids        Condensate
                                (MMcf)            (MBbls)          (MBbls)
                              -----------       -----------      ----------
       Hugoton                     46,821             3,315             -
       West Panhandle              19,268             2,978             211
       Gulf of Mexico              17,909               163             665
       Other                            3                 4              63
                              -----------      ------------      ----------
             Total                 84,001             6,460             939
                              ===========      ============      ==========

       Productive Wells. The following table sets forth information about Mesa's
gross and net  interests  in  productive  oil and gas wells,  excluding  royalty
wells, as of December 31, 1996.

                          PRODUCTIVE OIL AND GAS WELLS
                             As of December 31, 1996

                                                     Gross             Net
                                                   ---------        ---------
          Onshore U.S.:
               Kansas                                  1,432            990.0
               Texas                                     616            463.9
               Wyoming                                     2              -
               North Dakota                               20              3.8
               Other                                      13              1.3
                                                   ---------        ---------
                    Total Onshore                      2,083          1,459.0
                                                   ---------        ---------
          Offshore U.S.:
               Louisiana                                 192             43.4
               Texas                                      68             12.4
                                                   ---------        ---------
                    Total Offshore                       260             55.8
                                                   ---------        ---------
          Grand Total                                  2,343          1,514.8
                                                   =========        =========
                                       7

<PAGE>



       Acreage.   The  following  table  sets  forth  information  about  Mesa's
developed and undeveloped leasehold acreage as of December 31, 1996.

                                LEASEHOLD ACREAGE
                             As of December 31, 1996

                                 Producing                  Undeveloped
                                  Acreage                     Acreage
                         ------------------------     -----------------------
                           Gross         Net            Gross         Net
                         ----------   -----------     ----------   ----------
Onshore U.S.:
      Kansas                258,801       231,312          5,880        5,880
      Texas                 241,218       185,550            480          156
      Wyoming                11,477         4,365         14,570        9,035
      North Dakota            4,661         3,532          3,771        2,488
      Other                   2,564         2,142         16,123        6,518
                         ----------    ----------     ----------   ----------
        Total Onshore       518,721       426,901         40,824       24,077
                         ----------    ----------     ----------   ----------
Offshore U.S.:
      Louisiana              82,024        45,180         48,750       30,783
      Texas                  73,808        18,848         46,080       46,080
                         ----------    ----------     ----------   ----------
        Total Offshore      155,832        64,028         94,830       76,863
                         ----------    ----------     ----------   ----------
Grand Total                 674,553       490,929        135,654      100,940
                         ==========    ==========     ==========   ===========

Credit Facility Agreements

       On  August  7,  1997,  Parker  &  Parsley's  successor,  Pioneer  Natural
Resources  USA,  Inc.  (the  "Borrower"),   entered  into  two  Credit  Facility
Agreements  ("Credit  Facility  Agreements")  with a  syndicate  of  banks  (the
"Banks") that  refinanced the credit  facilities of Parker & Parsley and Mesa as
of the date of merger of the two companies.  One Credit Facility  Agreement (the
"Primary  Facility")  provides for a $1.1 billion credit facility.  The maturity
date for the Primary  Facility  is August 7, 2002.  The second  Credit  Facility
Agreement (the "364-day  Facility")  provides for a $300 million credit facility
with a maturity date of August 5, 1998. The Borrower has the option to renew the
364-day  Facility  for  another  period  of 364 days by  notifying  the Banks in
writing of such  election  not more than 60 days and not less than 45 days prior
to the maturity date.  The prior credit  agreements of Parker & Parsley and Mesa
were  paid in  full  following  the  Mergers  utilizing  proceeds  from  initial
borrowings against the new Primary Facility of $675 million.

       Advances  on  both  Credit  Facility  Agreements  bear  interest,  at the
Borrower's  option,  based on (a) the prime rate of NationsBank of Texas,  N.A.,
(b) a Eurodollar rate (substantially  equal to the London Interbank Offered Rate
("LIBOR")),  adjusted for the reserve  requirement as determined by the Board of
Governors  of the  Federal  Reserve  System  with  respect  to  transactions  in
Eurocurrency liabilities ("LIBOR Rate"), or (c) a competitive bid rate as quoted
by the Banks  electing to  participate  pursuant  to a request by the  Borrower.
Advances that are LIBOR Rate have periodic maturities, at the Borrower's option,
of one, two, three,  six, nine or twelve months.  Maturities of greater than six
months are subject to  availability  of such  deposits in the relevant  markets.
Advances  that  are  competitive  bid  rate  have  periodic  maturities,  at the
Borrower's option, of not less than 15 days nor more than 360 days. The interest
rates on LIBOR Rate advances  vary with  interest  rate margins  ranging from 18
basis points to 45 basis  points.  The interest  rate margin is  determined by a
grid based upon Pioneer's senior unsecured long-term public debt rating.

       The obligations of the Borrower under the Credit Facility  Agreements are
guaranteed by Pioneer and certain of its  subsidiaries  unless and to the extent
any such subsidiary has been designated as an  "Unrestricted  Subsidiary" by the
Borrower pursuant to the Credit Facility Agreements. Certain subsidiaries of the
Borrower which have not been  designated as Unrestricted  Subsidiaries  have not
provided guaranties because either (a) such guaranty would result in adverse tax
consequences  pursuant to Section 956 of the Internal  Revenue Code of 1986,  as
amended, or (b) such subsidiary is prohibited from executing a guaranty pursuant
to  contractual  restrictions.  In these cases,  the Borrower and certain of its
subsidiaries have pledged a portion of the issued and outstanding  capital stock
of such  subsidiaries  as security for the obligations of the Borrower under the
Credit Facility Agreements.

                                       8


<PAGE>



       The Credit Facility Agreements contain various restrictive  covenants and
compliance requirements,  which include (a) minimum financial requirements;  (b)
limits on the  incurrence of additional  indebtedness;  and (c)  limitations  on
mergers.

       Pioneer's  Unaudited Pro Forma Combined Balance Sheet as of June 30, 1997
includes $2.5 million of unamortized  capitalized  issuance fees associated with
Parker & Parsley's  existing bank credit  facility.  As a result of the new $1.4
billion dollar bank credit facility for Pioneer,  such  unamortized fees will be
recognized as noncash charges during the third quarter of 1997.

       After the consummation of the Mergers, Pioneer will have four outstanding
debt issuances in addition to the new credit  facilities  described above.  Such
debt issuances consist of (i) $150 million aggregate  principal amount of 8 7/8%
senior  notes  issued  by Parker &  Parsley  in 1995 and due in 2005,  (ii) $150
million  aggregate  principal  amount of 8 1/4% senior  notes issued by Parker &
Parsley in 1995 and due in 2007, (iii) $325 million  aggregate  principal amount
of 10 5/8%  Senior  Subordinated  Notes  issued by Mesa in 1996 and due 2006 and
(iv) $264  million  aggregate  principal  amount of 11 5/8% Senior  Subordinated
Discount Notes issued by Mesa in 1996 and due 2006.  These four issuances are or
will be  guaranteed  by Pioneer (the parent of Pioneer  Natural  Resources  USA,
Inc.) subsequent to the Mergers.

Vote of Security Holders

       On August 7, 1997,  Parker & Parsley and Mesa each held a Special Meeting
for their  respective  stockholders  in Dallas,  Texas.  At both  meetings,  the
following  three proposals were submitted for vote to the  stockholders:  (i) to
approve and adopt the Merger  Agreement dated as of April 6, 1997 among Parker &
Parsley,  Mesa and its  subsidiaries  Pioneer and MOC,  which  provides  for the
business  combination  of Parker & Parsley and Mesa (as a result of the business
combination,  Mesa, which is a Texas corporation, will reincorporate to Delaware
by  merging  into  Pioneer  and Parker & Parsley  will merge into MOC),  (ii) to
approve  the  adoption  of the  Pioneer  Long-Term  Incentive  Plan and (iii) to
approve the adoption of the Pioneer Employee Stock Purchase Plan.  Additionally,
stockholders of Mesa were asked to consider and vote upon a separate proposal to
approve the adoption of the Mesa 1996 Incentive  Plan. Each of the proposals was
approved by Parker & Parsley's and Mesa's stockholders as follows:
<TABLE>

 Parker & Parsley
<CAPTION>
                                                                                        Broker
 Proposal                                         For        Against       Abstain     Non-Votes
 --------                                     ----------    ----------    ---------    ---------
<S>                                           <C>           <C>           <C>          <C>               
Merger Agreement                              26,837,927       116,119      162,228          -
Long-Term Incentive Plan                      17,625,487     9,206,701      284,086          -
Employee Stock Purchase Plan                  26,254,862       582,103      279,309          -

 Mesa
                                                                                        Broker
 Proposal                                         For        Against       Abstain     Non-Votes
 --------                                     ----------    ---------     ---------    ---------
Merger Agreement
 Common stockholders of Mesa                  45,946,840     1,068,821    2,259,454          -
 Preferred Series A stockholders of Mesa      36,054,385     8,953,770    4,125,626          -
 Preferred Series B stockholders of Mesa      62,424,436           -            -            -

Pioneer Long-Term Incentive Plan
 Common stockholders of Mesa                  39,505,930     6,668,536    3,100,649          -
 Preferred Series A stockholders of Mesa      34,019,452     7,940,429    7,173,900          -
 Preferred Series B stockholders of Mesa      62,424,436           -            -            -

Employee Stock Purchase Plan
 Common stockholders of Mesa                  43,605,373     2,614,233    3,055,509          -
 Preferred Series A stockholders of Mesa      38,146,770     3,797,918    7,189,093          -
 Preferred Series B stockholders of Mesa      62,424,436           -            -            -

Mesa Incentive Plan
 Common stockholders of Mesa                  35,657,052    10,554,566    3,063,497          -
 Preferred Series A stockholders of Mesa      33,186,078     8,762,547    7,185,156          -
 Preferred Series B stockholders of Mesa      62,424,436           -            -            -
</TABLE>

                                        9

<PAGE>



              Unaudited Pro Forma Combined Financial Statements of
                        Pioneer Natural Resources Company


Item 7.        Financial Statements and Exhibits:

Financial Statements of Acquired Entity and Pro Forma Financial Information

       The  unaudited  pro  forma  combined  balance  sheet  and  statements  of
operations  have  been  prepared  to give  effect  to  certain  transactions  as
described below.

       The unaudited pro forma combined  balance sheet of Pioneer as of June 30,
       1997 has been  prepared  to give  effect  to (i) the  Mergers  as if such
       transactions  had  occurred  on June  30,  1997 (in  accordance  with the
       provisions of APB No. 16, "Business Combinations",  the Mergers have been
       accounted  for as a purchase  of Mesa by Parker &  Parsley)  and (ii) the
       conversion  of  Parker  &  Parsley's  6 1/4%  Cumulative  Monthly  Income
       Convertible  Preferred  Shares  ("Preferred  Shares")  to Pioneer  common
       stock.

       The unaudited pro forma combined  statements of operations of Pioneer for
       the six months  ended June 30, 1997 and for the year ended  December  31,
       1996 have been prepared to give effect to the Mergers and certain  events
       described  below for Parker & Parsley and Mesa as if the Mergers and such
       events had occurred on January 1, 1996.

       Pro Forma  Parker & Parsley  has been  prepared to give effect to (i) the
       sale of certain  wholly-owned  Australian  subsidiaries in March 1996 and
       the sale of Bridge Oil Timor Sea,  Inc. in June 1996  (collectively,  the
       "Australasian  Assets  Sold"),  (ii) the aggregate  effect of the sale of
       certain  nonstrategic  domestic  oil  and  gas  properties,  gas  plants,
       contract rights and related assets sold during the period from January 2,
       1996 to December  31, 1996  (collectively,  the "1996  Assets  Sold") and
       (iii) the exchange of Parker & Parsley's 6 1/4% Cumulative Monthly Income
       Convertible Preferred Shares ("Preferred Shares") to Pioneer common stock
       in August 1997.

       Pro Forma Mesa has been prepared to give effect to the  Recapitalization,
       which entailed  issuing $265 million in new preferred equity and repaying
       and refinancing substantially all of Mesa's $1.2 billion of then existing
       long-term  debt, and the acquisition of Greenhill,  including  additional
       borrowings to finance such acquisition.

       The unaudited pro forma combined financial statements included herein are
not  necessarily  indicative  of the results  that might have  occurred  had the
transactions  taken place at the  beginning of the period  specified and are not
intended to be a projection of future results.  In addition,  future results may
vary significantly from the results reflected in the accompanying  unaudited pro
forma  combined  financial  statements  because of normal  production  declines,
changes  in  product  prices,  future  acquisitions  and  divestitures,   future
development and exploration activities, and other factors.

       The following unaudited pro forma combined financial statements should be
read in conjunction  with (i) the  Consolidated  Financial  Statements  (and the
related  notes) of both Parker & Parsley and Mesa  included in their  respective
Annual Reports on Form 10-K and Form 10-K/A for the year ended December 31, 1996
and their respective  Quarterly  Reports on Form 10-Q for the three months ended
March  31,  1997  and for the six  months  ended  June  30,  1997  and  (ii) the
Historical  Financial Statements of Greenhill for the fiscal year ended June 30,
1996 and for the six months ended December 31, 1996  (unaudited) and the related
notes  thereto which are included in Mesa's  Current  Report on Form 8-K/A dated
February 7, 1997.

                                       10

<PAGE>


                        PIONEER NATURAL RESOURCES COMPANY

                   UNAUDITED PRO FORMA COMBINED BALANCE SHEET
                               as of June 30, 1997
                                 (in thousands)
<TABLE>
                                     ASSETS
<CAPTION>
                                                                       Pro Forma
                                            Parker &                    Combined          Pro Forma
                                            Parsley         Mesa       Adjustments        Combined
                                           ----------    ----------    -----------       ----------
<S>                                        <C>           <C>           <C>               <C>
Current assets:
   Cash and cash equivalents               $    9,843    $   20,751        (20,000) (a)  $   10,594
   Restricted cash                              1,723           -                             1,723
   Accounts receivable                         71,010        45,077                         116,087
   Inventories                                  5,581         3,130                           8,711
   Deferred income taxes                        9,300           -                             9,300
   Other current assets                         1,955         1,874                           3,829
                                            ---------     ---------                       ---------
        Total current assets                   99,412        70,832                         150,244
                                            ---------     ---------                       ---------
Property, plant and equipment, at cost:
   Oil and gas properties, using the
      successful efforts method of
      accounting:
        Proved properties                   1,536,665     2,293,133         (2,560) (a)   3,827,238
        Unproved properties                    41,071        44,000                          85,071
   Natural gas processing facilities           50,770           -                            50,770
   Accumulated depletion, depreciation
      and amortization                       (489,143)     (996,687)       996,687  (a)    (489,143)
                                            ---------     ---------                       ---------
                                            1,139,363     1,340,446                       3,473,936
                                            ---------     ---------                       ---------
Other property and equipment, net              28,552        11,286                          39,838
Other assets, net                              16,175        82,894        (35,516) (a)      57,691
                                                                            (5,862) (b)
                                            ---------     ---------                       ---------
                                           $1,283,502    $1,505,458                      $3,721,709
                                            =========     =========                       =========

                      LIABILITIES AND STOCKHOLDERS' EQUITY
                              Current liabilities:
   Current maturities of long-term debt    $    6,064    $    5,305                      $   11,369
   Undistributed unit purchases                 1,723           -                             1,723
   Accounts payable                            64,616        30,209                          94,825
   Domestic and foreign income taxes            2,038           -                             2,038
   Other current liabilities                   14,737        23,436                          38,173
                                            ---------     ---------                       ---------
        Total current liabilities              89,178        58,950                         148,128
                                            ---------     ---------                       ---------
Long-term debt, less current maturities       349,457     1,102,999         83,539  (a)   1,535,995
Other noncurrent liabilities                   27,336        80,032                         107,368
Deferred income taxes                          73,800           -          139,020  (a)     212,820

Preferred stock of subsidiary                 188,820           -         (188,820) (b)         -

Stockholders' equity:
   Preferred stock                                -           1,266         (1,266) (a)         -
   Common stock                                   370           643           (345) (a)         736
                                                                                68  (b)
   Additional paid-in capital                 465,234       667,860        276,911  (a)   1,592,895
                                                                           182,890  (b)
   Treasury stock, at cost                    (34,460)          -           34,460  (a)         -
   Unearned compensation                         (712)          -                              (712)
   Retained earnings (deficit)                124,479      (406,292)       406,292  (a)     124,479
                                            ---------     ---------                       ---------
        Total stockholders' equity            554,911       263,477                       1,717,398
                                            ---------     ---------                       ---------
Commitments and contingencies
                                            ---------     ---------                       ---------
                                           $1,283,502    $1,505,458                      $3,721,709
                                            =========     =========                       =========
</TABLE>
  See accompanying notes to unaudited pro forma combined financial statements.

                                       11
<PAGE>



                        PIONEER NATURAL RESOURCES COMPANY

              UNAUDITED PRO FORMA COMBINED STATEMENT OF OPERATIONS
                         Six months ended June 30, 1997
                      (in thousands, except per share data)

<TABLE>
<CAPTION>
                                                                                  Pro Forma
                                           Parker &                               Combined      Pro Forma
                                           Parsley       Mesa       Greenhill    Adjustments    Combined
                                          ---------    ---------    ---------    -----------    ---------
<S>                                       <C>          <C>          <C>          <C>            <C>
Revenues:
   Oil and gas                            $ 198,626    $ 165,336    $  17,369                   $ 381,331
   Natural gas processing                    11,819          -            -                        11,819
   Interest and other                         2,833        4,693          147                       7,673
   Gain (loss) on disposition of
      assets, net                             2,637          (23)          41                       2,655
                                           --------     --------     --------                    --------
                                            215,915      170,006       17,557                     403,478
                                           --------     --------     --------                    --------
Cost and expenses:
   Oil and gas production                    55,392       44,457        6,641                     106,490
   Natural gas processing                     6,098          -            -                         6,098
   Depletion, depreciation and
     amortization:
      Oil and gas properties                 54,860       52,503        7,725         37,880(c)   152,968
      Other                                   4,649        4,007          -                         8,656
   Impairment of long-lived assets              -          2,907          -                         2,907
   Exploration and abandonments              18,415        8,067        4,059           (407)(d)   30,134
   General and administrative                14,990        9,277       13,318            407(d)    37,992
   Interest                                  20,154       48,335          -           (6,010)(b)   65,346
                                                                                      (2,562)(e)
                                                                                       5,429(f)
   Other                                        831        2,470          -                         3,301
                                           --------     --------     --------                    --------
                                            175,389      172,023       31,743                     413,892
                                           --------     --------     --------                    --------
Income (loss) from continuing
   operations before income taxes            40,526       (2,017)     (14,186)                    (10,414)
Income tax benefit (provision)              (14,500)         -            -           18,400(g)     3,900
                                           --------     --------     --------                    --------
Income (loss) from continuing
   operations                                26,026       (2,017)     (14,186)                     (6,514)
Dividends on preferred stock                    -        (11,105)         -           11,105(h)       -
                                           --------     --------     --------                    --------
Income (loss) from continuing
   operations attributable to
   common stock                           $  26,026    $ (13,122)   $ (14,186)                  $  (6,514)
                                           ========     ========     ========                    ========
Income (loss) per common share            $     .74    $    (.20)                               $    (.09)
                                           ========     ========                                 ========
Weighted average shares
   outstanding                               35,364       65,499                     (33,632)(i)   73,945
                                                                                       6,714(b)  ========
                                           ========     ========
</TABLE>

  See accompanying notes to unaudited pro forma combined financial statements.

                                       12

<PAGE>


<TABLE>

                        PIONEER NATURAL RESOURCES COMPANY

              UNAUDITED PRO FORMA COMBINED STATEMENT OF OPERATIONS
                          Year ended December 31, 1996
                      (in thousands, except per share data)


<CAPTION>
                                        Pro Forma                 Pro Forma
                                         Parker &    Pro Forma     Combined        Pro Forma
                                         Parsley       Mesa       Adjustments      Combined
                                        ---------    ---------    -----------      ---------
<S>                                     <C>          <C>          <C>              <C>
Revenues:
   Oil and gas                          $ 374,560    $ 371,280                     $ 745,840
   Natural gas processing                  23,184          -                          23,184
   Interest and other                      17,328       33,824                        51,152
   Gain on disposition of assets, net         -         11,966                        11,966
                                         --------     --------                      --------
                                          415,072      417,070                       832,142
                                         --------     --------                      --------
Cost and expenses:
   Oil and gas production                 101,545       97,617                       199,162
   Natural gas processing                  11,949          -                          11,949
   Depletion, depreciation and
     amortization:
     Oil and gas properties                95,628      130,370       76,933  (c)     302,931
     Other                                  9,001        4,919                        13,920
   Exploration and abandonments            20,187       12,772         (831) (d)      32,128
   General and administrative              26,631       41,016          831  (d)      68,478
   Interest                                28,700      105,266       (4,923) (e)     129,043
   Other                                    2,451        2,340                         4,791
                                         --------     --------                      --------
                                          296,092      394,300                       762,402
                                         --------     --------                      --------
Income from continuing operations
  before income taxes                     118,980       22,770                        69,740
Income tax provision                      (41,600)         -         15,800  (g)     (25,800)
                                         --------     --------                      --------
Income from continuing operations          77,380       22,770                        43,940

Dividends on preferred stock                  -        (21,880)      21,880  (h)         -
                                         --------     --------                      --------
Income from continuing operations
  attributable to common stock          $  77,380    $     890                     $  43,940
                                         ========     ========                      ========
Income per common share                 $    1.82    $     .01                     $     .59
                                         ========     ========                      ========
Weighted average shares
   outstanding                             42,448       64,164      (32,366) (i)      74,246
                                        =========    =========                     =========
</TABLE>

  See accompanying notes to unaudited pro forma combined financial statements.

                                       13

<PAGE>


<TABLE>

                       PARKER & PARSLEY PETROLEUM COMPANY

              UNAUDITED PRO FORMA COMBINED STATEMENT OF OPERATIONS
                          Year ended December 31, 1996
                      (in thousands, except per share data)

<CAPTION>
                                                  Australasian      1996                       Pro Forma
                                     Parker &        Assets        Assets       Pro Forma      Parker &
                                     Parsley          Sold          Sold       Adjustments      Parsley
                                    ---------     -----------     ---------    -----------    ---------
<S>                                   <C>           <C>             <C>          <C>            <C>
Revenues:
   Oil and gas                      $ 396,931     $   (10,591)    $ (11,780)                  $ 374,560
   Natural gas processing              23,814             -            (630)                     23,184
   Interest and other                  17,458            (130)          -                        17,328
   Gain on disposition of assets,
     net                               97,140         (83,260)      (13,880)                         -
                                     --------     -----------      --------                    --------
                                      535,343         (93,981)      (26,290)                    415,072
                                     --------     -----------      --------                    --------
Cost and expenses:
   Oil and gas production             110,334          (3,300)       (5,489)                    101,545
   Natural gas processing              12,528             -            (579)                     11,949
   Depletion, depreciation and
     amortization:
       Oil and gas properties         102,803          (3,917)       (3,258)                     95,628
       Other                            9,331            (300)          (30)                      9,001
   Exploration and abandonments        23,030          (1,435)       (1,408)                     20,187
   General and administrative          28,363          (1,732)          -                        26,631
   Interest                            46,155          (1,100)          -        (12,020) (b)    28,700
                                                                                  (4,335) (j)
   Other                                2,451             -             -                         2,451
                                     --------       ---------      --------                    --------
                                      334,995         (11,784)      (10,764)                    296,092
                                     --------    ------------      --------                    --------
Income (loss) from continuing
   operations before
   income taxes                       200,348         (82,197)      (15,526)                    118,980
Income tax benefit (provision)        (60,100)         16,000         5,400       (2,900) (g)   (41,600)
                                     --------       ---------      --------                    --------
Income (loss) from continuing
   operations                       $ 140,248     $   (66,197)    $ (10,126)                  $  77,380
                                     ========      ==========      ========                    ========
Income per share                    $    3.92                                                 $    1.82
                                     ========                                                  ========
Weighted average shares
   outstanding                         35,734                                      6,714  (b)    42,448
                                    =========                                                  ========

  See accompanying notes to unaudited pro forma combined financial statements.

                                       14

<PAGE>



</TABLE>
<TABLE>
                                    MESA INC.

              UNAUDITED PRO FORMA COMBINED STATEMENT OF OPERATIONS
                          Year ended December 31, 1996
                      (in thousands, except per share data)

<CAPTION>
                                                                               Pro Forma    Pro Forma
                                     Mesa      Recapitalization   Greenhill   Adjustments      Mesa
                                   ---------   ----------------   ---------   -----------   ----------
<S>                                <C>         <C>                <C>         <C>           <C>
Revenues:
   Oil and gas                     $ 300,336     $     -          $  70,944                 $  371,280
   Natural gas processing                -             -                -                          -
   Interest and other                 33,824           -                -                       33,824
   Gain on disposition of assets,
     net                              11,966           -                -                       11,966
                                    --------      --------         --------                  ---------
                                     346,126           -             70,944                    417,070
                                    --------      --------         --------                  ---------
Cost and expenses:
   Oil and gas production             74,518           -             23,099                     97,617
   Natural gas processing                -             -                -                          -
   Depletion, depreciation and
     amortization:
       Oil and gas properties         98,382           -             29,355        2,633 (c)   130,370
       Other                           4,919           -                -                        4,919
   Exploration and abandonments        5,431           -              7,341                     12,772
   General and administrative         31,473           -              9,543                     41,016
   Interest                          121,135       (34,530)(k)         (729)      19,390 (f)   105,266
   Other                               1,929           -                411                      2,340
                                    --------      --------         --------                  ---------
                                     337,787       (34,530)          69,020                    394,300
                                    --------      --------         --------                  ---------
Income from continuing operations
  before income taxes                  8,339        34,530            1,924                     22,770
Income tax provision                     -             -                -                          -
                                    --------      --------         --------                  ---------
Income from continuing operations      8,339        34,530            1,924                     22,770

Dividends on preferred stock          (9,522)      (12,358)(l)          -                      (21,880)
                                    --------      --------         --------                  ---------
Income (loss) from continuing
   operations attributable to
   common stock                    $  (1,183)    $  22,172        $   1,924                 $      890
                                    ========      ========         ========                  =========
Income (loss) per common share     $    (.02)                                               $      .01
                                    ========                                                 =========
Weighted average shares
   outstanding                        64,164                                                    64,164
                                   =========                                                ==========
</TABLE>
  The accompanying notes to unaudited pro forma combined financial statements.

                                       15

<PAGE>



                        PIONEER NATURAL RESOURCES COMPANY

                      NOTES TO UNAUDITED PRO FORMA COMBINED
                              FINANCIAL STATEMENTS
                       June 30, 1997 and December 31, 1996

  Note 1.   Basis of Presentation

      In accordance with the Merger  Agreement,  (i) holders of Parker & Parsley
  common stock  received one share of Pioneer  common stock for each share held;
  (ii) holders of Mesa common stock  received one share of Pioneer  common stock
  for every  seven  shares  held;  and (iii)  holders of Mesa Series A Preferred
  Stock and Mesa Series B Preferred Stock received 1.25 shares of Pioneer common
  stock for every seven shares held.  No  fractional  shares were issued and all
  treasury shares were canceled.

      The unaudited pro forma  combined  balance sheet of Pioneer as of June 30,
  1997 has been  prepared  to give  effect to the  Mergers  and the  exchange of
  Parker  &  Parsley's  Preferred  Shares  to  Pioneer  common  stock as if such
  transactions  had occurred on June 30, 1997. In accordance with the provisions
  of APB No. 16, "Business Combinations", the Mergers have been accounted for as
  a purchase of Mesa by Parker & Parsley.

      The unaudited pro forma  combined  statements of operations of Pioneer for
  the six months  ended June 30, 1997 and for the year ended  December  31, 1996
  have been prepared to give effect to the Mergers and certain events  described
  below for  Parker & Parsley  and Mesa as if the  Mergers  and such  events had
  occurred on January 1, 1996.

      Pro Forma Parker & Parsley has been prepared to give effect to the sale of
  the Australasian  Assets Sold, the 1996 Assets Sold and the exchange of Parker
  & Parsley's Preferred Shares to Pioneer common stock.

      Pro Forma Mesa has been  prepared to give  effect to the  Recapitalization
  and the acquisition of Greenhill,  including additional  borrowings to finance
  such acquisition.

      The following is a description of the individual columns included in these
  unaudited pro forma combined financial statements:

          Parker & Parsley - Represents the consolidated balance sheet of Parker
          &  Parsley  as of June 30,  1997 and the  consolidated  statements  of
          operations  of Parker & Parsley for the six months ended June 30, 1997
          and for the year ended December 31, 1996.

          Australasian  Assets Sold - Reflects the results of operations for the
          year ended  December 31, 1996 from certain  wholly-owned  subsidiaries
          prior to their  sale in 1996.  On March  28,  1996,  Parker &  Parsley
          completed  the sale of  certain  wholly-owned  subsidiaries  to Santos
          Ltd.,  and on June 20, 1996,  Parker & Parsley  completed  the sale of
          another  wholly-owned  subsidiary,  Bridge  Oil Timor  Sea,  Inc.,  to
          Phillips Petroleum  International  Investment Company. During the year
          ended  December  31,  1996,   Parker  &  Parsley  received   aggregate
          consideration  of $237.5 million for these combined sales.  The assets
          sold to Santos Ltd.  consisted  primarily of properties located in the
          Cooper  Basin in  Central  Australia,  the  Surat  Basin in  Northeast
          Australia, the Carnarvon Basin on the Northwest Shelf off the coast of
          Western  Australia,  the  Otway  Basin  off  the  coast  of  Southeast
          Australia and the Central Sumatra Basin in Indonesia.  At December 31,
          1995, Parker & Parsley's interests in these properties  contained 32.1
          million BOE of proved reserves (consisting of 12.4 million Bbls of oil
          and 118.3 Bcf of gas),  representing  $133.8  million of SEC 10 value.
          Prior to their sale in 1996, these properties produced 249,500 Bbls of
          oil and  1,927,000  Mcf of gas.  Parker & Parsley  received an average
          price of  $19.55  per Bbl of oil and  $1.95  per Mcf of gas from  such
          production  and  incurred  production  costs  per  BOE  of  $4.92  and
          depletion  expense per BOE of $5.84 related to these  properties.  The
          wholly-owned  subsidiary  sold  to  Phillips  Petroleum  International
          Investment  Company,  Bridge Oil Timor Sea,  Inc.,  has a wholly owned
          subsidiary, Bridge Oil Timor Sea Pty Ltd., which owns a 22.5% interest
          in the ZOCA 91-13 permit in the offshore Bonapart Basin in the Zone of
          Cooperation between Australia and Indonesia.

                                       16

<PAGE>


                        PIONEER NATURAL RESOURCES COMPANY

                      NOTES TO UNAUDITED PRO FORMA COMBINED
                              FINANCIAL STATEMENTS
                       June 30, 1997 and December 31, 1996



          1996 Assets Sold - Reflects  the  results of  operations  for the year
          ended  December  31,  1996 from  certain oil and gas  properties,  gas
          plants,  contract  rights and  related  assets  prior to their sale in
          1996.  During the year ended December 31, 1996,  Parker & Parsley sold
          certain domestic  nonstrategic oil and gas properties,  gas plants and
          other related  assets for aggregate  proceeds of  approximately  $58.4
          million.  Prior to their  sale in 1996,  these oil and gas  properties
          produced  274,314  Bbls of oil and  3,196,093  Mcf of  gas.  Parker  &
          Parsley  received an average  price of $19.30 per Bbl of oil and $2.03
          per Mcf of gas from such production and incurred  production costs per
          BOE of $6.80 and  depletion  expense per BOE of $4.04 related to these
          properties.

          Mesa - Represents  the  consolidated  balance sheet of Mesa as of June
          30, 1997 and the consolidated statements of operations of Mesa for the
          six months  ended June 30,  1997 and for the year ended  December  31,
          1996.

          Recapitalization  -  Represents  the effects on Mesa's  unaudited  pro
          forma combined statement of operations from the Recapitalization as if
          it had occurred on January 1, 1996. In August 1996,  Mesa  completed a
          recapitalization  of its  balance  sheet by  issuing  new  equity  and
          repaying  and  refinancing  substantially  all  of its  then  existing
          long-term  debt.  The  Recapitalization  was  undertaken by Mesa in an
          effort to  deleverage  and  recapitalize  Mesa through the issuance of
          additional  equity and through the refinancing of substantially all of
          Mesa's $1.2 billion debt existing prior to the  Recapitalization.  The
          Recapitalization  provided Mesa with an improved  financial  condition
          due to (i) a significant  reduction in total debt outstanding,  (ii) a
          reduction  in  annual  cash  interest  expense  of  approximately  $75
          million,  (iii)  cost  savings  programs  which  reduced  general  and
          administrative  and  other  overhead  expenses  by  approximately  $10
          million  annually,  and (iv) the  extension  of  maturities  on Mesa's
          long-term  debt,  which  eliminated  Mesa's  then  existing  liquidity
          concerns.  The Recapitalization  included (i) the private placement of
          shares  of a new  class of Mesa  Series  B  Preferred  Stock  for $133
          million to DNR - Mesa  Holdings,  Inc.  ("DNR"),  whose  sole  general
          partner is  Rainwater  Inc., a Texas  corporation  owned by Richard E.
          Rainwater, (ii) the sale of $132 million of a new class of Mesa Series
          A  Preferred  Stock to Mesa's  then  existing  stockholders  through a
          rights offering,  (ii) the establishment of a new bank credit facility
          and (iv) the issuance of two new series of senior subordinated notes.

          Greenhill - Represents  the  unaudited  statements  of  operations  of
          Greenhill  prior to its  acquisition by Mesa on April 15, 1997 and for
          the year ended December 31, 1996.

      The unaudited  pro forma  combined  statement of  operations  for the year
  ended  December  31,  1996  presented  herein  does not reflect the results of
  operations from Mesa's  acquisition  from MAPCO Inc. of approximately 11 MMBOE
  in  February  1997 for  approximately  $66  million.  The  acquisition  is not
  presented since it is not considered significant under Rule 3-05 of Regulation
  S-X. The  purchase was funded by  additional  borrowings  under Mesa's  credit
  facility.

                                       17

<PAGE>


                        PIONEER NATURAL RESOURCES COMPANY

                      NOTES TO UNAUDITED PRO FORMA COMBINED
                              FINANCIAL STATEMENTS
                       June 30, 1997 and December 31, 1996


  Note 2.    Acquisition of Mesa

      The  aggregate  Pioneer  common stock  purchase  consideration,  including
  non-recurring  merger  transaction  costs,  is computed in accordance with the
  exchange ratios agreed to in the Merger Agreement as follows:
<TABLE>
<CAPTION>

                                                  Mesa        Mesa Series     Mesa Series
                                                 Common       A Preferred     B Preferred
                                                  Stock          Stock           Stock           Total
                                              ------------    ------------    ------------    ------------
<S>                                           <C>             <C>             <C>             <C>       
    Shares outstanding                          64,279,568      62,884,094      63,672,925
    Exchange ratio for Mesa shares                    1.00            1.25            1.25
                                               -----------     -----------     -----------
                                                64,279,568      78,605,118      79,591,156     222,475,842
    Exchange ratio to Pioneer common stock            7.00            7.00            7.00            7.00
                                               -----------     -----------     -----------     -----------
    Pioneer Shares                               9,182,795      11,229,303      11,370,165      31,782,263
    Value of Pioneer common stock (a)         $      30.82    $      30.82    $      30.82    $      30.82
                                               -----------     -----------     -----------     -----------
    Pioneer common stock consideration        $283,013,742    $346,087,118    $350,428,485     979,529,345
                                               ===========     ===========     ===========
    Cash consideration for nonrecurring
       merger transaction costs                                                                 20,000,000
                                                                                               -----------
    Aggregate purchase consideration                                                          $999,529,345
                                                                                               ===========
  ------------------
</TABLE>
  (a)  Pioneer  Common  Stock is  valued at $30.82  per share  which  represents
       Parker &  Parsley's  seven-day  average  trading  price  surrounding  the
       announcement of the Mergers on April 7, 1997.

      The following  table  represents the  preliminary  allocation of the total
  purchase  price of Mesa to the acquired  assets and  liabilities  of Mesa. The
  allocation  represents  the fair values  assigned  to each of the  significant
  assets  acquired  and  liabilities  assumed.  Any  future  adjustments  to the
  allocation  of the purchase  price are not  anticipated  to be material to the
  unaudited pro forma combined financial statements.
                                                               Allocation of
                                                                 Aggregate
                                                                 Purchase
                                                               Consideration
                                                               -------------
                                                               (in thousands)

     Net working capital                                       $      11,882
     Property, plant and equipment                                 2,334,573
     Other assets                                                     58,664
     Long-term debt                                               (1,186,538)
     Other noncurrent liabilities, including deferred taxes         (219,052)
                                                                ------------
                                                               $     999,529
                                                                ============
     Pioneer Common Stock consideration                        $     979,529
     Cash paid for nonrecurring merger transaction costs              20,000
                                                                ------------
     Aggregate purchase consideration                          $     999,529
                                                                ============

                                       18

<PAGE>


                        PIONEER NATURAL RESOURCES COMPANY

                      NOTES TO UNAUDITED PRO FORMA COMBINED
                              FINANCIAL STATEMENTS
                       June 30, 1997 and December 31, 1996


      The following  table  illustrates  the number of Pioneer  shares that were
  issued  in  accordance  with  the  exchange  ratios  agreed  to in the  Merger
  Agreement.

                                    Shares           New
                                Outstanding at     Pioneer
   Existing Security Type       August 7, 1997    Security      Pioneer Shares
- -----------------------------   --------------   ------------   --------------
Parker & Parsley Common Stock     41,773,238     Common Stock     41,773,238
Mesa Common Stock                 64,279,568     Common Stock      9,182,795
Mesa Series A Preferred Stock     62,884,094     Common Stock     11,229,303
Mesa Series B Preferred Stock     63,672,925     Common Stock     11,370,165
                                                                 -----------
                                                                  73,555,501
                                                                 ===========
  Note 3.    Pro Forma Entries

  (a) To record the acquisition of Mesa using the purchase method of accounting.
      The  allocation  of  the  purchase  price  to  the  acquired   assets  and
      liabilities is preliminary and,  therefore,  subject to change. Any future
      adjustments to the allocation of the purchase price are not anticipated to
      be material to Pioneer's financial statements. (See Note 2 above).

  (b) To (i) reclassify the Preferred  Shares and related  capitalized  issuance
      fees to common stock and additional  paid-in capital as a result of Parker
      &  Parsley's  mandatory  exchange of such  Preferred  Shares for shares of
      Parker & Parsley  common  stock on July 28,  1997 and (ii)  eliminate  the
      interest expense associated with such Preferred Shares and amortization of
      capitalized  issuance fees. On July 28, 1997,  Parker & Parsley  exercised
      its right to require  each  holder of the  3,776,400  Preferred  Shares to
      mandatorily  exchange all  Preferred  Shares for shares of common stock of
      Parker &  Parsley  at a rate of 1.7778  shares of Parker & Parsley  common
      stock for each Preferred Share. As a result of the exchange,  Pioneer will
      no longer incur  interest  expense of  approximately  $12 million per year
      associated with the Preferred Shares.

  (c) To  adjust  depreciation,  depletion  and  amortization  expense  for  the
      additional  basis  allocated  to the oil and gas  properties  acquired and
      accounted for using the successful efforts method of accounting.

  (d) To  reclassify  certain  amounts to conform with the  financial  statement
presentation of Pioneer.

  (e) To  reduce  interest  expense  for (i) the  amortization  of the  premiums
      (utilizing  the  effective  interest  rate  method)  recorded  as  part of
      purchase  accounting  for Mesa's  10-5/8%  Senior  Subordinated  Notes and
      11-5/8% Senior  Subordinated  Discount  Notes and (ii) the  application of
      Parker  &  Parsley's  excess  cash  in  1996 to the  reduction  of  Mesa's
      outstanding  bank  indebtedness  at  Mesa's  1996  pro  forma  incremental
      borrowing interest rate of 7% (see pro forma entry (j) below).

  (f) To adjust  interest  expense  resulting  from the  borrowing  of the funds
      necessary for Mesa's  acquisition  of Greenhill.  Mesa's 1997 and 1996 pro
      forma incremental  borrowing interest rate of 7% was utilized to determine
      the additional pro forma interest expense.

  (g) To adjust income tax expense for each tax jurisdiction.

  (h) To eliminate the preferred stock dividends associated with Mesa's Series A
and Series B Preferred Stock.

                                       19

<PAGE>


                        PIONEER NATURAL RESOURCES COMPANY

                      NOTES TO UNAUDITED PRO FORMA COMBINED
                              FINANCIAL STATEMENTS
                       June 30, 1997 and December 31, 1996


  (i) To adjust the weighted  average shares  outstanding for the acquisition of
      Mesa. This  adjustment  also assumes the conversion of Mesa's  outstanding
      employee stock options into Pioneer employee stock options for purposes of
      computing weighted average shares outstanding.

  (j) To adjust interest expense  resulting from the application of that portion
      of the  sales  proceeds  from the  Australasian  Assets  Sold and the 1996
      Assets  Sold  necessary  to retire  Parker &  Parsley's  outstanding  bank
      indebtedness.   The  proceeds   applied  to  retire   Parker  &  Parsley's
      outstanding  bank  indebtedness of $225 million resulted in a reduction in
      interest  expense of $4.3 million.  The reduction in interest  expense was
      calculated  utilizing Parker & Parsley's weighted average rate on its bank
      indebtedness of 6.22% for the period during 1996 in which Parker & Parsley
      had outstanding bank indebtedness.

  (k) To reduce interest expense as a result of the  Recapitalization.  Interest
      expense  adjustments include the following for the year ended December 31,
      1996:
                                                                     Pro Forma
                                          Historical    Pro Forma    Adjustment
                                          ----------    ---------    ----------
  Interest expense on former debt repaid
   in the Recapitalization:
    Secured Notes                         $   26,231          -      $ (26,231)
    Former Credit Agreement                    2,472          -         (2,472)
    12-3/4% secured discount notes            43,979          -        (43,979)
    13-1/2% subordinated notes                   654          -           (654)

  Interest expense on former debt repaid
   prior to the Recapitalization:
    12-3/4% unsecured discount notes           2,595    $   2,595          -

  Interest expense on new debt issued in
   the Recapitalization:
    10-5/8% Senior Subordinated Notes         17,613       35,418       17,805
    11-5/8% Senior Discount Notes              8,893       18,661        9,768
    New Credit Facility                       15,094       26,327       11,233

  Other interest expense                       3,604        3,604          -
                                           ---------     --------     --------
                                          $  121,135    $  86,605    $ (34,530)
                                           =========     ========     ========

      Other  interest   expense  is  primarily  the  interest   portion  of  the
      administrative   fee  charged  by  Colorado   Interstate  Gas  Company  in
      connection with Mesa's West Panhandle field operations.  The interest rate
      on the New  Credit  Facility  is  approximately  7.73% on the  first  $250
      million due to an interest  rate swap with the balance at a floating  rate
      that during the period outstanding was approximately 7%.

  (l) To record the pro forma  adjustment for an 8% annual  dividend on the Mesa
      Series A and Series B Preferred  Stock  payable  quarterly  in  additional
      shares  of Mesa  Series A and  Series B  Preferred  Stock for at least the
      first  four  years  after  issuance  as if the Mesa  Series A and Series B
      Preferred Stock had been issued January 1, 1996.

  Note 4.   Income Taxes

      Pioneer will account for income taxes in accordance with the provisions of
  SFAS 109. In  accordance  with SFAS 109,  Pioneer  will  prepare  separate tax
  calculations  for each tax  jurisdiction  in which  Pioneer will be subject to
  income taxes.

                                       20

<PAGE>


                        PIONEER NATURAL RESOURCES COMPANY

                      NOTES TO UNAUDITED PRO FORMA COMBINED
                              FINANCIAL STATEMENTS
                       June 30, 1997 and December 31, 1996


  Note 5.   Income from Continuing Operations per Share

      Income  from  continuing  operations  per share is  computed  based on the
  weighted   average   number  of  shares  of  common  stock  and  common  stock
  equivalents,  if more than 3% dilutive,  outstanding during the period.  Fully
  diluted income from  continuing  operations  per share is not presented  since
  dilution is less than 3% on a pro forma combined basis. Income from continuing
  operations  per share  reflects the  exchange of Parker & Parsley's  Preferred
  Shares and the conversion of Mesa's Series A Preferred Stock and Mesa's Series
  B Preferred Stock to Pioneer common stock which increased the weighted average
  number of shares of Pioneer common stock outstanding to 73.6 million at August
  7, 1997.

  Note 6.   Parker & Parsley Stock Options

      Upon the consummation of the Mergers on August 7, 1997, which  constituted
  a "Change of Control" as defined in the Parker & Parsley  Long-term  Incentive
  Plan, each holder of Parker & Parsley options was granted  corresponding stock
  appreciation  rights  unless  such  holder had waived  such right prior to the
  Mergers, and all outstanding stock appreciation rights and options immediately
  became fully vested and  exercisable in full.  Consequently,  during the third
  quarter of 1997, Pioneer will record  compensation  expense in accordance with
  APB No. 25,  "Accounting for Stock Issued to Employees"  equal to the value of
  the stock  appreciation  rights granted of approximately $2.5 million dollars,
  before  income tax  effects,  based on a common  stock  price of $37.69.  This
  expense is associated  with the stock  appreciation  rights granted to certain
  individuals  who are no longer with Pioneer and who elected to not waive their
  right and receive stock appreciation rights. In accordance with SEC guidelines
  concerning the preparation of pro forma financial statements,  this adjustment
  is not reflected in the accompanying Pro Forma Combined Financial Statements.

  Note 7.   General and Administrative Expense Reductions

      Mesa's general and administrative expenses for the year ended December 31,
  1996 includes $9.4 million  associated  with the  elimination  of 86 positions
  from the total of 385 at December 31, 1995,  and a  significant  downsizing of
  Mesa's  natural  gas  vehicle  equipment  business  in  conjunction  with  the
  Recapitalization.  Given the first  quarter  1997  general and  administrative
  expenses  of  $3.8  million,   Mesa's   continuing   costs  are  estimated  at
  approximately $15 million per year ($3.8 million multiplied by four quarters).
  In addition, Greenhill's general and administrative expenses prior to its sale
  to Mesa on April 15, 1997 of $13.3 million  included  severance  costs paid to
  Greenhill  employees  of  approximately  $11  million  as few  of  Greenhill's
  administrative  personnel  were  retained.  As  a  result,  Mesa  considers  a
  continuing   annual   expense   associated   with   Greenhill   properties  of
  approximately $5 million to be reasonable. Given the above, Mesa expects total
  general and  administrative  expenses to approximate $20 million per year. The
  accompanying  Pro Forma  Combined  Statements of Operations for Pioneer do not
  include any  adjustments  related to the expected level of ongoing general and
  administrative expense.

  Note 8.   Parker & Parsley Third Quarter of 1997 Charges

      Pioneer's  Unaudited Pro Forma Combined  Balance Sheet as of June 30, 1997
  includes  certain  unamortized  amounts  which will be  recognized  as noncash
  charges  during the third  quarter of 1997 as a result of the  Mergers.  These
  amounts include $2.5 million (pre-tax) of capitalized issuance fees associated
  with Parker & Parsley's  existing bank credit facility which was replaced by a
  new $1.4 billion bank credit facility for Pioneer and $544 thousand  (pre-tax)
  of unearned  compensation  resulting from certain change of control provisions
  included in Parker & Parsley's existing  Long-term  Incentive Plan whereby the
  vesting requirements of outstanding restricted stock awards were accelerated.

                                       21

<PAGE>


                        PIONEER NATURAL RESOURCES COMPANY

                      NOTES TO UNAUDITED PRO FORMA COMBINED
                              FINANCIAL STATEMENTS
                       June 30, 1997 and December 31, 1996


  Note 9.   Oil and Gas Reserve Data

      The following unaudited pro forma supplemental  information  regarding the
  oil and gas  activities  of Pioneer is  presented  pursuant to the  disclosure
  requirements  promulgated  by the SEC and  Statement of  Financial  Accounting
  Standards No. 69,  "Disclosures About Oil and Gas Producing  Activities".  The
  pro forma  combined  reserve  information  is  presented as if the sale of the
  Australasian  Assets  and 1996  Assets  Sold and the  acquisition  of Mesa and
  Greenhill had occurred on January 1, 1996.

      Management  emphasizes that reserve estimates are inherently imprecise and
  subject to revision and that estimates of new  discoveries  are more imprecise
  than those of producing oil and gas properties. Accordingly, the estimates are
  expected to change as future information becomes available; such changes could
  be significant.

  Quantities of oil and gas reserves

      Set  forth  below  is a pro  forma  summary  of the  changes  in  the  net
  quantities  of oil and natural gas  reserves  for the year ended  December 31,
  1996.
                                               Oil, NGL's and
                                                 Condensate         Gas
                                                   (Bbls)          (Mcf)
                                               --------------    ----------
                                                       (in thousands)

     Balance, January 1, 1996                      267,108        1,984,726
       Revisions of previous estimates              31,475           42,246
       Purchase of minerals-in-place                   300           11,494
       New discoveries and extensions                3,952           31,259
       Production                                  (20,550)        (160,729)
                                                 ---------       ----------
     Balance, December 31, 1996                    282,285        1,908,996
                                                 =========       ==========

  Standardized measure of discounted future net cash flows

      The pro forma combined  standardized measure of discounted future net cash
  flow  is  computed  by  applying   year-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 oil and gas reserves less
  estimated  future  expenditures  (based on  year-end  costs) to be incurred in
  developing and producing the proved  reserves,  discounted using a rate of 10%
  per year to reflect the  estimated  timing of the future  cash  flows.  Future
  income taxes are calculated by comparing  discounted  future cash flows to the
  tax basis of oil and gas properties, plus available carryforwards and credits,
  and applying the current tax rate to the difference.

                                             December 31, 1996
                                             -----------------
                                              (in thousands)

  Oil and gas producing activities:
    Future cash inflows                       $  14,015,758
    Future production costs                      (3,978,622)
    Future development costs                       (394,157)
    Future income tax expense                    (2,679,935)
                                               ------------
                                                  6,963,044
    10% annual discount factor                   (3,247,780)
                                               ------------
    Standardized measure of discounted
      future net cash flows                   $   3,715,264
                                               ============

                                       22

<PAGE>


                        PIONEER NATURAL RESOURCES COMPANY

                      NOTES TO UNAUDITED PRO FORMA COMBINED
                              FINANCIAL STATEMENTS
                       June 30, 1997 and December 31, 1996


Changes relating to the standardized measure of discounted future net cash flows

     The principal sources of the change in the pro forma combined  standardized
  measure of  discounted  future net cash flows for the year ended  December 31,
  1996 are as follows (in thousands):

     Oil and gas sales, net of production costs                $   (546,678)
     Net changes in prices and production costs                   1,979,347
     Extensions and discoveries                                      94,936
     Purchases of minerals-in-place                                  20,606
     Revisions of estimated future development costs                (83,116)
     Revisions of previous quantity estimates                       364,334
     Accretion of discount                                          253,122
     Changes in production rates, timing and other                 (132,538)
                                                                -----------
     Change in present value of future net revenues               1,950,013
     Net change in present value of future income taxes            (566,915)
                                                                -----------
                                                                  1,383,098
     Balance, beginning of year                                   2,332,166
                                                                -----------
     Balance, end of year                                      $  3,715,264
                                                                ===========
                                       23

<PAGE>



                                    MESA INC.






  Exhibits

2.1  Amended  and  Restated  Agreement  and Plan of Merger  dated as of April 6,
     1997,  by  and  between   among  Mesa  Inc.,   Mesa   Operating   Co.,  MXP
     Reincorporation  Corp. and Parker & Parsley Petroleum Company (incorporated
     by  reference  to Exhibit 2.1 to  Pioneer's  Form S-4 dated June 27,  1997,
     Registration No. 333-26951).

10.1 Credit  Facility  Agreement  (Primary  Facility) dated as of August 7, 1997
     between Pioneer Natural  Resources USA, Inc. as Borrower and NationsBank of
     Texas,  N.A., as Administrative  Agent, CIBC Inc., as Documentation  Agent,
     Morgan Guaranty Trust Company of New York, as  Documentation  Agent and The
     Chase Manhattan Bank, as Syndication  Agent;  Bank of America Natural Trust
     and Savings  Association,  The Bank of New York,  The Bank of Nova  Scotia,
     Royal  Bank of  Canada,  Union  Bank of  California,  N.A.,  The Fuji Bank,
     Limited  -Houston  Agency and Wells Fargo Bank,  N.A.,  as  Co-Agents;  and
     certain  other  lenders  (incorporated  by  reference  to  Exhibit  10.1 to
     Pioneer's Form 8-K dated August 21, 1997, Registration No. 333-26951).

10.2 Credit  Facility  Agreement  (364 Day Facility)  dated as of August 7, 1997
     between Pioneer Natural  Resources USA, Inc. as Borrower and NationsBank of
     Texas,  N.A., as Administrative  Agent, CIBC Inc., as Documentation  Agent,
     Morgan Guaranty Trust Company of New York, as  Documentation  Agent and The
     Chase Manhattan Bank, as Syndication  Agent;  Bank of America Natural Trust
     and Savings  Association,  The Bank of New York,  The Bank of Nova  Scotia,
     Royal  Bank of  Canada,  Union  Bank of  California,  N.A.,  The Fuji Bank,
     Limited  -Houston  Agency and Wells Fargo Bank,  N.A.,  as  Co-Agents;  and
     certain  other  lenders  (incorporated  by  reference  to  Exhibit  10.2 to
     Pioneer's Form 8-K dated August 21, 1997, Registration No. 333-26951).




                                       24

<PAGE>


                                    MESA INC.



                               S I G N A T U R E S


  Pursuant to the  requirements  of the  Securities  Exchange  Act of 1934,  the
  Registrant  has duly  caused  this  report to be  signed on its  behalf by the
  undersigned hereunto duly authorized.

                                       MESA INC.

                                       By:  Pioneer Natural Resources Company,
                                            its successor by merger





  Date:     August 21, 1997        By:     /s/ Garrett Smith
                                       ------------------------------------
                                           M. Garrett Smith
                                           Senior Vice President, Finance




                                       25

<PAGE>


      Exhibit Index                                                       Page
      -------------                                                       ----

2.1   Amended and Restated Agreement and  Plan of Merger dated as of
      April 6, 1997,  by and between among Mesa Inc., Mesa Operating
      Co.,  MXP Reincorporation Corp. and Parker & Parsley Petroleum
      Company (incorporated by reference to Exhibit 2.1 to Pioneer's
      Form S-4 dated June 27, 1997, Registration No. 333-26951).

10.1  Credit Facility Agreement (Primary Facility) dated as of August
      7, 1997 between Pioneer Natural Resources USA, Inc. as Borrower
      and NationsBank of Texas, N.A.,  as Administrative Agent,  CIBC
      Inc., as Documentation Agent,  Morgan Guaranty Trust Company of
      New York,  as Documentation Agent and The Chase Manhattan Bank,
      as Syndication Agent; Bank of America Natural Trust and Savings
      Association,  The Bank of  New York,  The Bank of  Nova Scotia,
      Royal Bank of Canada, Union  Bank of California, N.A., The Fuji
      Bank, Limited - Houston Agency and Wells Fargo Bank,  N.A.,  as
      Co-Agents; and certain other lenders (incorporated by reference
      to Exhibit 10.1 to  Pioneer's  Form 8-K dated August 21,  1997,
      Registration No. 333-26951).

10.2  Credit Facility Agreement (364 Day Facility) dated as of August
      7, 1997 between Pioneer Natural Resources USA, Inc. as Borrower
      and NationsBank of Texas,  N.A., as Administrative  Agent, CIBC
      Inc., as Documentation  Agent, Morgan Guaranty Trust Company of
      New York,  as Documentation Agent and The Chase Manhattan Bank,
      as Syndication Agent; Bank of America Natural Trust and Savings
      Association,  The Bank  of New York,  The Bank of Nova  Scotia,
      Royal Bank of Canada, Union Bank of California, N.A.,  The Fuji
      Bank, Limited - Houston Agency and Wells Fargo Bank,  N.A.,  as
      Co-Agents; and certain other lenders (incorporated by reference
      to Exhibit 10.2 to Pioneer's  Form 8-K dated  August 21,  1997,
      Registration No. 333-26951).


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