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<PAGE>
 
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<S>                             <C>
<PERIOD-TYPE>                   6-MOS
<FISCAL-YEAR-END>                          DEC-31-1998
<PERIOD-START>                              JAN-1-1998
<PERIOD-END>                               JUN-30-1998
<CASH>                                          16,305
<SECURITIES>                                         0
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<PP&E>                                         743,844
<DEPRECIATION>                               (307,291)
<TOTAL-ASSETS>                                 654,567
<CURRENT-LIABILITIES>                           74,907
<BONDS>                                        133,330
<PREFERRED-MANDATORY>                                0
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<OTHER-SE>                                     325,889
<TOTAL-LIABILITY-AND-EQUITY>                   654,567
<SALES>                                        224,030
<TOTAL-REVENUES>                               228,128
<CGS>                                          193,713
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<OTHER-EXPENSES>                                 1,138
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<INCOME-TAX>                                     2,303
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<DISCONTINUED>                                       0
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                     3,756
<EPS-PRIMARY>                                     0.16
<EPS-DILUTED>                                     0.16
        

</TABLE>
