The year is 2010. Barack Obama is beginning the second year of his presidency, oil prices are hovering around $80 a barrel, and Congress is hotly debating an ambitious carbon reduction program known as cap and trade. Enter NRG Energy, one of the country’s largest power companies, with headquarters in Houston and West Windsor Township, New Jersey. Reading the writing on the wall, NRG decides to get out in front of a potential carbon tax by building the world’s largest carbon capture and storage unit on top of a coal-fired power plant it owns in Fort Bend County, southwest of Houston.

In March 2010 the U.S. Department of Energy announces it will contribute $154 million towards the cost of the project, which it hopes will advance carbon capture technology and serve as a model for other coal plants around the country. (It ended up contributing about $190 million.) The remainder of the plant’s approximately $1 billion cost is fronted by NRG, Japanese energy company JX Nippon Oil & Gas Exploration, and two Japanese government banks. “Everyone knew there was going to be a price on carbon, and we knew we were moving towards a carbon-free world,” said NRG communications director David Knox. “So our thinking was, how can we get ahead of this and be on the ground floor of carbon capture?”

Best of all, from NRG’s perspective, the plant would be self-financing—the captured CO2 would be compressed into liquid form and pumped eighty miles southwest through a dedicated pipeline to the West Ranch Oil Field, where it would be injected into depleted oil reservoirs to force any remaining oil to the surface, a process known as enhanced oil recovery. (The consortium had partnered with Houston-based Hilcorp Energy to manage the pipeline and oil field.) The recovered oil would pay for the costs of the carbon capture unit, plus a tidy profit for NRG and its partners.

The carbon capture unit, dubbed Petra Nova, broke ground in 2014. But as it went up, the assumptions upon which it was based were crumbling. The cap and trade bill died in Congress, killing environmentalists’ dream of a carbon tax. After rising to a peak of $114 a barrel in March 2014, oil prices began to fall back to earth, bottoming out at $34 in February 2016 before rebounding to their present level around $55—high enough to cover operating costs for the plant, but not enough to turn a profit. Donald Trump’s election as president, and his choice of Rick Perry for energy secretary, meant the likely loss of any future subsidies for carbon capture.

Despite the setbacks, NRG forged ahead, and on December 29, 2016, the Petra Nova plant finally came on line—on time and on budget. According to NRG, the plant is currently capturing over ninety percent of the carbon released by the power plant’s flue gas—about 5,200 tons of CO2 per day. That CO2 is being piped to the West Ranch Oil Field, where it’s being used to recover oil left behind from previous drilling, after which the CO2 is permanently sequestered underground. Although Hilcorp hasn’t released figures for the field’s current productivity, it aims to produce around 15,000 barrels a day at full capacity.

Petra Nova has managed to avoid many of the problems plaguing previous carbon capture efforts, such as the Kemper County power plant in Mississippi, which is two years behind schedule and $4 billion over budget. Cost overruns at the Kemper plant forced its owner, Southern Company, to raise electricity rates in Mississippi, drawing the ire of state residents. NRG doesn’t have that option, because in Texas’s deregulated electricity market, customers can simply switch to a cheaper competitor.

“There’s plenty of technology out there for capturing CO2, but doing it in a way that doesn’t affect the cost of electricity is the issue,” said NRG vice president for development David Greeson, who oversaw the construction of Petra Nova. “Everything NRG does is subject to competitive customer choice. If we raise our costs, consumers are going to choose someone else.”

Charles McConnell, who served as Assistant Secretary of Energy from 2011 to 2013 and is now executive director of Rice University’s Energy and Environment Initiative, sees carbon capture units like Petra Nova as the single best way for the world to meet the ambitious targets for CO2 emissions set by the 2016 Paris Climate Agreement. “I think if we have any shot at all of reaching the climate change targets by 2050, it’s through carbon capture, utilization, and sequestration,” he said. “If we don’t do it, we ain’t going to get there—there’s just not enough impact from the other things [like transitioning to renewable energy sources] that can get this done. It’s got to be all of the above, we have to have a comprehensive approach, but we need to embrace this technology.”

But many environmentalists are wary of carbon capture technology. “We have this problem we don’t like, which is CO2 emissions,” said Mark Floegel, research director at Greenpeace. “But rather than finding a way to avoid producing that CO2, we try to find a way to reuse the CO2 to make more CO2, and in order to do that we need more infrastructure. That’s just a terrible investment. If you look at the cost curves for renewable energy, they are quickly becoming competitive with fossil fuels, to the point where they will soon be cheaper on an absolute scale, even with oil in its current slump.”

Bill McKibben, the journalist and environmental activist, was even blunter, arguing that the complexity of carbon capture “makes Rube Goldberg look like a Scandinavian minimalist designer.” Environmentalists also cite concerns about the safety of transporting the CO2 to oilfields and storing it in underground geological formations.

Right now, though, the biggest threat to carbon capture technology isn’t environmentalists; it’s energy economists who don’t see the point in investing in expensive technology that can’t turn a profit—not with oil at $55 a barrel and the Trump administration slashing coal regulations. Without seismic shifts in the price of oil or the regulatory environment, Petra Nova may remain the world’s largest carbon capture unit for the foreseeable future.