Electric power output slipped 12.5 percent in July from a year earlier, reflecting declining demand for air conditioning amid lower-than-average temperatures nationwide, the Federation of Electric Power Companies said in a preliminary report Friday.

The fall was the first since July 2002 and the biggest since May 1972, when the nation's electric power industry was reorganized into 10 major companies, federation officials said.

In July, the volume of power supplied by the nation's 10 major power companies, including those generated by wholesalers, totaled 78.05 billion kilowatt-hours, the federation said.

All but Okinawa Electric Power Co. reported declines, with Tokyo Electric Power Co. recording the biggest drop of 16.9 percent following a cool summer.