Plugging and abandoning (P&Aing) wells is a policy priority because unplugged wells present potential financial and environmental risks to the public. Offshore wells, compared with land wells, generally produce more, cost more to P&A and present different environmental risks. Here we estimate that the cost to P&A all 14,000 unplugged, non-producing wells in US Gulf of Mexico offshore waters, inland waters and wetlands is US$30 billion. Wells in shallower waters closer to shore make up 90% of inactive wells but only 25% of total P&A costs. They also present larger environmental risks. Prior owners of wells in federal waters (deeper and farther from shore) can be held liable for P&A costs if the current owner does not P&A them. We find that 88% of outstanding P&A liability in federal waters is associated with wells currently or formerly owned by one of the large, financially stable ‘supermajor’ companies.
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