California leaned more heavily on natural gas-fired electricity during the extreme heat wave that blanketed the state earlier this month, according to the Energy Information Administration (EIA).

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Grid operator CAISO (aka California Independent System Operator) had to urge customers to cut back on electricity use during an extended stretch of sweltering temperatures in early September as demand edged perilously close to available supply.

The heat wave also sent regional natural gas spot prices soaring. SoCal Citygate day-ahead prices averaged as high as $15.870/MMBtu on Aug. 31, NGI’s Daily Gas Price Index historical data show.

Driven by air-conditioning use, demand in CAISO’s territory peaked on Sept. 6, setting a new record high in the process, according to a research...