<TABLE> <S> <C>

<PAGE>

<ARTICLE> 5
<RESTATED>
<MULTIPLIER> 1,000

<S>                             <C>                     <C>                     <C>                     <C>
<PERIOD-TYPE>                   12-MOS                   9-MOS                   6-MOS                   3-MOS
<FISCAL-YEAR-END>                          DEC-31-1997             DEC-31-1997             DEC-31-1997             DEC-31-1997
<PERIOD-END>                               DEC-31-1997             SEP-30-1997             JUN-30-1997             MAR-31-1997
<CASH>                                          10,200                  14,400                  17,400                  22,800
<SECURITIES>                                         0                       0                       0                       0
<RECEIVABLES>                                  244,100                 193,800                 296,500                 299,900
<ALLOWANCES>                                         0                       0                       0                       0
<INVENTORY>                                      9,900                  10,700                  13,000                  10,300
<CURRENT-ASSETS>                               288,900                 302,000                 374,400                 373,600
<PP&E>                                       5,189,800               4,985,700               4,831,300               4,760,700
<DEPRECIATION>                               3,598,400               3,519,500               3,447,000               3,387,800
<TOTAL-ASSETS>                               1,924,800               1,788,600               1,758,700               1,746,500
<CURRENT-LIABILITIES>                          359,500                 327,700                 326,600                 386,900
<BONDS>                                        672,100                 636,300                 643,300                 630,300
<PREFERRED-MANDATORY>                                0                       0                       0                       0
<PREFERRED>                                          0                       0                       0                       0
<COMMON>                                         1,000                   1,000                   1,000                   1,000
<OTHER-SE>                                     504,500                 444,800                 399,000                 348,000
<TOTAL-LIABILITY-AND-EQUITY>                 1,924,800               1,788,600               1,758,700               1,746,500
<SALES>                                      3,306,600               2,672,500               1,868,000               1,104,500
<TOTAL-REVENUES>                             3,333,900               2,693,000               1,883,100               1,106,400
<CGS>                                          492,500                 358,800                 237,200                 117,900
<TOTAL-COSTS>                                  668,000                 493,200                 334,100                 188,700
<OTHER-EXPENSES>                             2,320,200               1,947,700               1,369,600                 822,800
<LOSS-PROVISION>                                     0                       0                       0                       0
<INTEREST-EXPENSE>                              47,800                  35,900                  24,400                  13,000
<INCOME-PRETAX>                                234,600                 169,500                 123,800                  67,200
<INCOME-TAX>                                   (5,900)                 (4,100)                   2,600                   4,300
<INCOME-CONTINUING>                            240,500                 173,600                 121,200                  62,900
<DISCONTINUED>                                       0                       0                       0                       0
<EXTRAORDINARY>                                      0                       0                       0                       0
<CHANGES>                                            0                       0                       0                       0
<NET-INCOME>                                   240,500                 173,600                 121,200                  62,900
<EPS-BASIC>                                       2.47                    1.78                    1.25                    0.65
<EPS-DILUTED>                                     2.46                    1.78                    1.25                    0.65



</TABLE>