<TABLE> <S> <C>

<PAGE>
<ARTICLE> 5
<RESTATED> 
<MULTIPLIER> 1,000
       
<S>                             <C>                     <C>                     <C>
<PERIOD-TYPE>                                    3-MOS                   3-MOS                   3-MOS
<FISCAL-YEAR-END>                          DEC-31-1997             DEC-31-1997             DEC-31-1997
<PERIOD-START>                             JAN-01-1997             APR-01-1997             JUL-01-1997
<PERIOD-END>                               MAR-31-1997             JUN-30-1997             SEP-30-1997
<CASH>                                          56,079                  16,536                  13,925
<SECURITIES>                                         0                       0                       0
<RECEIVABLES>                                   56,148                  60,777                  72,823
<ALLOWANCES>                                       229                     229                       0
<INVENTORY>                                      4,520                   6,008                   3,765
<CURRENT-ASSETS>                               117,609                  85,127                  91,477
<PP&E>                                         759,707                 832,042                 904,533
<DEPRECIATION>                                 208,621                 224,382                 243,041
<TOTAL-ASSETS>                                 672,636                 696,658                 756,763
<CURRENT-LIABILITIES>                           76,662                  90,266                  92,791
<BONDS>                                        151,930                 151,269                 201,066
<PREFERRED-MANDATORY>                                0                       0                       0
<PREFERRED>                                          0                       0                       0
<COMMON>                                           314                     314                     314
<OTHER-SE>                                     687,546                 396,290                 401,609
<TOTAL-LIABILITY-AND-EQUITY>                   672,636                 696,658                 756,763
<SALES>                                         75,302                  70,007                  88,361
<TOTAL-REVENUES>                                76,552                  71,220                  89,167
<CGS>                                           38,297                  37,050                  53,552
<TOTAL-COSTS>                                   52,364                  54,875                  71,886
<OTHER-EXPENSES>                                 5,977                   6,173                   6,414
<LOSS-PROVISION>                                     0                       0                       0
<INTEREST-EXPENSE>                               2,223                   3,095                   3,403
<INCOME-PRETAX>                                 15,988                   7,077                   7,464
<INCOME-TAX>                                     6,075                   2,690                   2,836
<INCOME-CONTINUING>                              9,913                   4,387                   4,628
<DISCONTINUED>                                       0                       0                       0
<EXTRAORDINARY>                                      0                       0                       0
<CHANGES>                                            0                       0                       0
<NET-INCOME>                                     9,913                   4,387                   4,628
<EPS-PRIMARY>                                      .32                     .14                     .15
<EPS-DILUTED>                                      .31                     .14                     .14
        

</TABLE>