A few months ago at the Paris climate talks, President Barack Obama and a panoply of world leaders talked at length about the importance of reducing carbon dioxide pollution associated with burning coal, the largest source of greenhouse gases. So far there is only one way to do that without pulling the plug on coal altogether: carbon capture and storage (CCS), a process by which CO 2 is pulled from a smokestack before it escapes into the air and is then buried deep underground.

Nearly every plan to mitigate global warming includes CCS, yet few countries have adopted the technology because there is little incentive to make the costly investment. Decades ago, however, the U.S. found a clever way to make the method economically viable: tie CCS to oil recovery. And while the scheme seemed to work, low oil prices now are putting CCS—and therefore almost all climate cleanup plans—in jeopardy.

Oil-field workers first pumped carbon dioxide down into oil wells in 1972. Called enhanced oil recovery (EOR), the technique boosts the amount of petroleum that a well yields because the gas eases the flow of the oil, restores pressure underground to force more oil to the surface, and slips into nooks and crannies that other aids, such as water, will simply flow around. During the process, a portion of CO 2 becomes trapped underground like the oil before it. “It will stay there for eternity,” says Richard Esposito, a geologist who has worked to develop CCS at the coal-burning electric utility Southern Company.

This arrangement—using CO 2 to get oil—is one of the few ways to make carbon capture pay, says Julio Friedmann, the principal deputy assistant secretary for fossil energy at the U.S. Department of Energy. “EOR has been the dominant storage mode because it produces revenue,” he explains. In other words, it potentially satisfies oil companies and environmentalists. With money to be made, a handful of EOR projects popped up across the U.S. over the past few decades. For example, at the Tinsley oil field in Mississippi, the oil and natural gas company Denbury Resources began flooding wells with CO 2 in March 2008 and now recycles some 670 million cubic feet (19 million cubic meters) of the gas every day—increasing its oil production from 50 barrels a day to more than 9,000 barrels a day.

In fact, Denbury and several other companies using EOR need so much CO 2 that they recently contracted to buy the pollution from a new coal-fired power plant in Kemper County, Mississippi—the ultimate goal of the scheme. Such so-called anthropogenic CO 2 now makes up roughly a quarter of all the CO 2 used for this type of oil recovery (the rest comes from natural deposits trapped in geologic domes).

The relationship between CCS and EOR is fragile, however. Because the price of oil has dipped so dramatically over the past couple of years, burying CO 2 no longer pays. Plummeting prices have made it difficult for EOR companies to bring in enough money to pay for new machinery, such as pumps, compressors and specialized pipelines, says Dan Cole, Denbury's vice president of commercial development and governmental relations. Already oil-field services giant Schlumberger has shut down its Carbon Services unit, which was supposed to turn CO 2 into a steady business, and others are considering similar moves. Those closures could throw a wrench into the climate cleanup efforts carefully laid out in recent reports by the International Energy Agency and the Intergovernmental Panel on Climate Change.

At the same time, the troubled relationship may highlight the irony of crafting planet-saving scenarios that rely on oil extraction. After all, burning the extra oil produced by pumping CO 2 underground produces more CO 2 that ends up in the atmosphere, causing yet more global warming.