For well over a century, the oil and gas industry has drilled holes across California in search of black gold and a lucrative payday. But with production falling steadily, the time has come to clean up many of the nearly quarter-million wells scattered from downtown Los Angeles to western Kern County and across the state.

The bill for that work, however, will vastly exceed all the industry’s future profits in the state, according to a first-of-its-kind study published Thursday and shared with ProPublica.

“This major issue has sneaked up on us,” said Dwayne Purvis, a Texas-based petroleum reservoir engineer who analyzed profits and cleanup costs for the report. “Policymakers haven’t recognized it. Industry hasn’t recognized it, or, if they have, they haven’t talked about it and acted on it.”

The analysis, which was commissioned by Carbon Tracker Initiative, a financial think tank that studies how the transition away from fossil fuels impacts markets and the economy, used California regulators’ draft methodology for calculating the costs associated with plugging oil and gas wells and decommissioning them along with related infrastructure. The methodology was developed with feedback from the industry.

The report broke down the costs into several categories. Plugging wells, dismantling surface infrastructure and decontaminating polluted drill sites would cost at least $13.2 billion, based on publicly available data. Adding in factors with slightly more uncertainty, like inflation rates and the price of decommissioning miles of pipeline, could bring the total cleanup bill for California’s onshore oil and gas industry to $21.5 billion.

Meanwhile, California oil and gas production will earn about $6.3 billion in future profits over the remaining course of operations, Purvis estimated.

Compounding the problem, the industry has set aside only about $106 million that state regulators can use for cleanup when a company liquidates or otherwise walks away from its responsibilities, according to state data. That amount equals less than 1% of the estimated cost.

Read the full article about cleaning up the oil and gas industry by Mark Olalde at ProPublica.