The largest methane leak in US history has left southern California facing potential power outages this summer, with state officials warning that gas-run power plants could run short of fuel when electricity use spikes.

The Aliso Canyon gas reservoir belched methane into the skies over Los Angeles for four months, releasing an estimated 100,000 tons of the potent greenhouse gas before being plugged in February. And without the huge volumes of gas it normally holds, the region could find itself running short of juice on more than a dozen days this summer, state experts reported this week.

"It's essential to deliver gas in the winter, when people want to heat their homes and use gas for cooking and heating water," California Energy Commission spokesman Albert Lundeen said. "But in the summertime, the gas is used to produce electricity, and it's especially called upon when there's higher demand."

Power plants that burn natural gas provided about 48 percent of the state's electricity in 2015, Lundeen said. During the hot southern summers, when air conditioners are cranked up, those plants would dip into the Aliso Canyon reservoir to keep their generators spinning. Not only did that gas keep the lights on and air conditioners churning out cold air, it kept pressure in the lines high enough to keep fuel flowing to all customers.

"There are other storage facilities," he said. "They're just not anywhere near as large. So Aliso Canyon is essential to the structure of the system today."

But since the blowout, the reservoir is down to about 15 billion cubic feet of gas — a fraction of the 86 billion it holds when full. And with it out of commission, state agencies warned that there might not be enough fuel to keep the lights on when power use peaks. And using past years as a model, a report from the California Public Utilities Commission, the Energy Commission, the agency that manages the state power grid, and two Los Angeles-area utilities found there could be as many as 14 days this summer when that might happen.

"Without supply available from Aliso Canyon, a loss of capacity or difference between expected supply and actual demand greater than 5 percent of the total demand is likely to lead to gas system curtailments," the agencies concluded.

That happened twice in 2015, when the reservoir was fully operational. A total of 17 power plants tap into Aliso Canyon, according to reservoir owner Southern California Gas, and shortfalls this year might mean problems not only in the Los Angeles area, but as far south as San Diego, the report found. And drawing too much on the reservoir could endanger fuel supplies for the winter if the facility isn't back online before then, the report states.

To head off that risk, the agencies recommended a list of 18 steps they said would reduce — but not eliminate — the risk of shortages. Those steps range from better managing the gas remaining in the reservoir to urging both residential and commercial customers to conserve energy.

Californians are already used to "Flex Alerts" — calls to conserve power during the day, when demand is at its highest, and those are expected to be used again, Lundeen said.

"There's a lot of steps that will be enacted to help mitigate the risk that we foresee," he said.

But the Environmental Defense Fund (EDF), which has been raising alarms about methane leaks from natural gas infrastructure and helped illustrate the extent of the Aliso Canyon leak, said the problem highlights the risk of relying on a potent greenhouse gas as a basic fuel.

"Out of this crisis, important reforms to the gas market are needed to allow renewable energy, demand response and other low-carbon technologies to compete with natural gas – paving the way for safer, cleaner and more resilient energy," Tim O'Connor, the EDF's California oil and gas director, said in a statement on Tuesday's report.

"And under no circumstances should Aliso Canyon ever be returned to service, even for a short period of time, if the company and the state cannot guarantee that it will be operated safely and with zero leaks, and provide hard evidence to that effect," he said

[**Related:** Obama Tells Oil and Gas Companies to Get a Grip on Methane Emissions](Obama Tells Oil and Gas Companies to Get a Grip on Methane Emissions)[](Obama Tells Oil and Gas Companies to Get a Grip on Methane Emissions)