Despite the largest methane leak in U.S. history, Southern California Gas Co.’s fourth quarter earnings nearly doubled, the utility reported Friday during a conference call.

During last year’s fourth quarter, SoCalGas’ earnings increased 88 percent from a year earlier to $143 million, the company said.

The increase was “due primarily to the impact of seasonality on revenues, which added $48 million of earnings during the most recent quarter,” the company said in a statement, referring to the spell of colder weather that pushed bills upward.

For all of 2015, SoCalGas’ full-year earnings were $419 million, up from $332 million in 2014, due mainly to a lower effective tax rate, including a favorable resolution of prior years’ income-tax matters.

The leak at a well in the company’s Aliso Canyon storage facility above Porter Ranch was discovered on Oct. 23, 2015, and it pumped more that 100,000 tons of methane into the air before being sealed 111 days later, according to scientists at UC Davis.

RELATED STORY: Read a story about pollution from the Aliso Canyon storage facility.

An estimated 15,000 residents voluntarily evacuated from the community at gas company expense. The utility gave residents up to $7,000 a month to live in hotels or rental housing.

Those in hotels and similar lodging initially had eight days to return home after the state declared the well sealed Feb. 18. But a judge on Thursday ruled that timeline for residents to return home would be extended to March 18.

The company is appealing that ruling.

The company said that, at one point, 6,400 households were in temporary housing and that costs associated are estimated to be $330 million, said Debra L. Reed, chairman and CEO of SoCalGas’s parent company Sempra Energy during an conference call with analysts.

Most of the costs associated with relocating residents and stopping the leak will be covered by four insurance policies totaling more than $1 billion, she said.

“We are pleased SoCalGas was able to permanently stop the Aliso Canyon natural gas leak last week,” Reed said. “We recognize the disruption the leak has caused to SoCalGas customers living in the neighborhoods adjacent to the Aliso Canyon facility. SoCalGas is committed to helping local residents return to their normal lives as quickly as possible and also will support forward-looking regulations to ensure the safety of natural gas storage operations going forward.

“Despite this operational challenge at SoCalGas, we produced strong financial results in 2015,” she said. “We successfully grew operating earnings and outperformed our adjusted earnings guidance for the year. Looking forward, our key capital projects and initiatives are progressing well, and we are executing our five-year financial plan, which we expect will generate earnings growth at about twice the utility industry average.”

The well was declared sealed by the California Department of Conservation on Feb. 18.

“There were 15 bcf (billion cubic feet) of gas in the field and it is stable,” Reed said.

Both Reed and SoCalGas President and CEO Dennis Arriola said that the company is cooperating with the investigation now underway by the state’s Department of Conservation’s Division of Oil, Gas & Geothermal Resources, the California Public Utilities Commission and an independent third party, Blade Energy Partners.

The company is also inspecting the 115 wells in Aliso according to stringent guidelines issued by state division.

It was unclear when the cause of the leak will finally be know or when the field could come back online.

“They are really driving the timeline,” Arriola said of the two agencies and Blade.

Sempra reported 2015 earnings of $1.35 billion, up from $1.16 billion a year earlier.