<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM FORM 10-Q AS
OF SEPTEMBER 30, 1997 AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH
FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
       
                                                  
<PERIOD-TYPE>                   3-MOS                   6-MOS
<FISCAL-YEAR-END>                          DEC-31-1997             DEC-31-1997
<PERIOD-START>                             JUL-01-1997             JAN-01-1997
<PERIOD-END>                               SEP-30-1997             SEP-30-1997
<CASH>                                               0                       0
<SECURITIES>                                         0                       0
<RECEIVABLES>                                  162,542<F1>             162,542
<ALLOWANCES>                                         0                       0
<INVENTORY>                                          0                       0
<CURRENT-ASSETS>                               216,839                 216,839
<PP&E>                                         781,819                 781,819
<DEPRECIATION>                                 187,509                 187,509
<TOTAL-ASSETS>                               1,213,415               1,213,415
<CURRENT-LIABILITIES>                          218,248                 218,248
<BONDS>                                        350,000                 350,000
<PREFERRED-MANDATORY>                                0                       0
<PREFERRED>                                          0                       0
<COMMON>                                           786                     786
<OTHER-SE>                                     508,880                 508,880
<TOTAL-LIABILITY-AND-EQUITY>                 1,213,415               1,213,415
<SALES>                                              0                       0
<TOTAL-REVENUES>                               364,813               1,017,856
<CGS>                                                0                       0
<TOTAL-COSTS>                                  213,476                 596,549
<OTHER-EXPENSES>                               105,791                 292,246
<LOSS-PROVISION>                                     0                       0
<INTEREST-EXPENSE>                               8,538                  22,226
<INCOME-PRETAX>                                 37,008                 106,835
<INCOME-TAX>                                    14,433                  42,364
<INCOME-CONTINUING>                             22,575                  64,471
<DISCONTINUED>                                       0                       0
<EXTRAORDINARY>                                      0                       0
<CHANGES>                                            0                       0
<NET-INCOME>                                    22,575                  64,471
<EPS-PRIMARY>                                     0.26                    0.75
<EPS-DILUTED>                                     0.26                    0.74
<FN>
<F1>Trade accounts receivable, less allowance for doubtful accounts.
</FN>