<PAGE>
 
            NOTES TO CONSOLIDATED FINANCIAL STATEMENTS--(CONTINUED)
 
NOTE 14. OIL AND GAS OPERATIONS (UNAUDITED)--(CONTINUED)

<TABLE>
<CAPTION>
                                                       UNITED
                                                       STATES  BOLIVIA  TOTAL
                                                      -------- ------- --------
                                                           (IN THOUSANDS)
<S>                                                   <C>      <C>     <C>
1992
  Estimated future cash flows Revenues from
   hydrocarbon sales................................. $106,284         $106,284
    Production costs.................................   27,059           27,059
    Development costs................................    8,860            8,860
                                                      --------   ---   --------
  Future net cash flows before income taxes..........   70,365           70,365
  Estimated income tax payments......................   12,545           12,545
                                                      --------   ---   --------
  Future net cash flows..............................   57,820           57,820
  10% discount.......................................   10,818           10,818
                                                      --------   ---   --------
  Standardized measure of discounted future net cash
   flows............................................. $ 47,002         $ 47,002
                                                      ========   ===   ========
</TABLE>

 
              CHANGES IN STANDARDIZED MEASURE OF DISCOUNTED FUTURE
                   NET CASH FLOWS RELATING TO PROVED RESERVES
 

<TABLE>
<CAPTION>
                                                      1994     1993     1992
                                                     -------  -------  -------
                                                         (IN THOUSANDS)
<S>                                                  <C>      <C>      <C>
Standardized measure, beginning of year--U.S........ $37,902  $47,002  $58,780
Standardized measure, beginning of year--Bolivia....  10,312
  Change in sales prices, net of production costs... (24,990)   8,163   (3,038)
  Costs incurred or transferred into the
   amortization pool during the period that reduced
   estimated future development costs...............   4,975             2,188
  Changes in estimated future development and
   abandonment costs................................  (4,638)  (4,679)    (660)
  Sales, net of production costs....................  (6,281) (11,369) (12,107)
  Revisions of quantity estimates...................   3,243   (1,800)  (4,260)
  Purchase of reserves in-place.....................            1,098
  Accretion of discount.............................   4,283    5,397    7,004
  Net change in income taxes........................    (149)   2,048    4,291
  Changes in production rates and other.............     588   (7,958)  (5,196)
                                                     -------  -------  -------
Standardized measure, end of year................... $25,245  $37,902  $47,002
                                                     =======  =======  =======
</TABLE>

 
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