<ARTICLE> UT
<LEGEND>
This schedule contains summary financial information extracted from the
balance sheet, statement of income and statement of cash flows contained in
Form 10-Q of Commonwealth Energy System for the three months ended June 30,
1999 and is qualified in its entirety by reference to such financial
statements.
</LEGEND>
<CIK> 0000071304
<NAME> COMMONWEALTH ENERGY SYSTEM
<MULTIPLIER> 1,000

                          
<FISCAL-YEAR-END>            DEC-31-1999
<PERIOD-END>                 JUN-30-1999
<PERIOD-TYPE>                      6-MOS
<BOOK-VALUE>                    PER-BOOK
<TOTAL-NET-UTILITY-PLANT>      1,019,352
<OTHER-PROPERTY-AND-INVEST>       14,033
<TOTAL-CURRENT-ASSETS>           320,518
<TOTAL-DEFERRED-CHARGES>         280,398
<OTHER-ASSETS>                   176,789
<TOTAL-ASSETS>                 1,811,090
<COMMON>                          43,081
<CAPITAL-SURPLUS-PAID-IN>        112,309
<RETAINED-EARNINGS>              304,409
<TOTAL-COMMON-STOCKHOLDERS-EQ>    459,799
<PREFERRED-MANDATORY>                  0
<PREFERRED>                            0
<LONG-TERM-DEBT-NET>             384,457
<SHORT-TERM-NOTES>                90,000
<LONG-TERM-NOTES-PAYABLE>              0
<COMMERCIAL-PAPER-OBLIGATIONS>          0
<LONG-TERM-DEBT-CURRENT-PORT>     35,696
<PREFERRED-STOCK-CURRENT>              0
<CAPITAL-LEASE-OBLIGATIONS>       10,576
<LEASES-CURRENT>                   1,120
<OTHER-ITEMS-CAPITAL-AND-LIAB>    829,442
<TOT-CAPITALIZATION-AND-LIAB>  1,811,090
<GROSS-OPERATING-REVENUE>        465,234
<INCOME-TAX-EXPENSE>              18,638
<OTHER-OPERATING-EXPENSES>       400,078
<TOTAL-OPERATING-EXPENSES>       418,716
<OPERATING-INCOME-LOSS>           46,518
<OTHER-INCOME-NET>                 5,023
<INCOME-BEFORE-INTEREST-EXPEN>     51,541
<TOTAL-INTEREST-EXPENSE>          23,344
<NET-INCOME>                      28,197
<PREFERRED-STOCK-DIVIDENDS>          222
<EARNINGS-AVAILABLE-FOR-COMM>     27,975
<COMMON-STOCK-DIVIDENDS>          17,908
<TOTAL-INTEREST-ON-BONDS>         17,008
<CASH-FLOW-OPERATIONS>            55,502
<EPS-BASIC>                       1.30
<EPS-DILUTED>                       1.30