The new estimate is contained in Thursday's release of second-quarter earnings by San Diego-based parent Sempra Energy.
The previous estimate in May was $665 million.
The gas leak reported Oct. 23 at Aliso Canyon spewed an estimated 107,000 tons of methane over 16 weeks.
Some 8,000 families were uprooted from nearby suburbs as foul-smelling gas wafted over neighborhoods, triggering complaints of headaches, nausea, nosebleeds and other symptoms.
Scientists say it was the largest-known release of climate-changing methane in U.S. history.
Area residents met with Gov. Jerry Brown's staff Wednesday in a campaign to permanently shut down the Aliso Canyon facility.