<TABLE> <S> <C>
<PAGE>
<ARTICLE> UT
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM THE
STATEMENTS OF INCOME, BALANCE SHEETS, AND STATEMENTS OF CASH FLOWS AND IS
QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> 9-MOS
<FISCAL-YEAR-END> DEC-31-1999
<PERIOD-END> SEP-30-2000
<BOOK-VALUE> PER-BOOK
<TOTAL-NET-UTILITY-PLANT> 3,580,849
<OTHER-PROPERTY-AND-INVEST> 601,455
<TOTAL-CURRENT-ASSETS> 654,299
<TOTAL-DEFERRED-CHARGES> 220,443
<OTHER-ASSETS> 163,516
<TOTAL-ASSETS> 5,220,562
<COMMON> 0
<CAPITAL-SURPLUS-PAID-IN> 125,561
<RETAINED-EARNINGS> 965,186
<TOTAL-COMMON-STOCKHOLDERS-EQ> 1,064,133<F1>
200,000
0
<LONG-TERM-DEBT-NET> 1,210,142
<SHORT-TERM-NOTES> 190
<LONG-TERM-NOTES-PAYABLE> 0
<COMMERCIAL-PAPER-OBLIGATIONS> 576,000
<LONG-TERM-DEBT-CURRENT-PORT> 248,174
0
<CAPITAL-LEASE-OBLIGATIONS> 0
<LEASES-CURRENT> 0
<OTHER-ITEMS-CAPITAL-AND-LIAB> 1,895,309<F1>
<TOT-CAPITALIZATION-AND-LIAB> 5,220,562
<GROSS-OPERATING-REVENUE> 2,107,930
<INCOME-TAX-EXPENSE> 66,590
<OTHER-OPERATING-EXPENSES> 1,853,006
<TOTAL-OPERATING-EXPENSES> 1,853,006
<OPERATING-INCOME-LOSS> 254,924
<OTHER-INCOME-NET> (12,576)<F2>
<INCOME-BEFORE-INTEREST-EXPEN> 187,571
<TOTAL-INTEREST-EXPENSE> 93,487
<NET-INCOME> 82,271
0
<EARNINGS-AVAILABLE-FOR-COMM> 82,271
<COMMON-STOCK-DIVIDENDS> 0
<TOTAL-INTEREST-ON-BONDS> 69,315
<CASH-FLOW-OPERATIONS> 399,297
<EPS-BASIC> 0
<EPS-DILUTED> 0
<FN>
<F1>NOTE 1 - ($26,614) THOUSAND OF COMMON STOCKHOLDERS' EQUITY IS CLASSIFIED AS
OTHER ITEMS-CAPITALIZATION AND LIABILITIES. THIS REPRESENTS LEVERAGED FORMER
NSP COMMON STOCK HELD BY THE EMPLOYEE STOCK OWNERSHIP PLAN.
<F2>NOTE 2 - INCLUDES OTHER INCOME (EXPENSE) AND DISTRIBUTIONS ON REDEEMABLE
PREFERRED SECURITIES OF SUBSIDIARY TRUST.
</FN>
</TABLE>
