“This was one of our highest-cost refineries, with a very low contribution to the bottom line,” he added. “All those things conspired to the conclusion that we needed to cease operations this year and start a process to redevelop the land for a higher-value use.”

But it’s not that simple, at least according to Deborah Sivas, a professor of environmental law at Stanford University.

Aging infrastructure, she said, could also cause oil production costs to increase, as could dwindling supplies of oil in the ground.

After a century of pumping oil, Sivas said, there isn’t much left in California. So refineries will put steam or hot water into the ground to make the oil viscous enough to pump.