When the Trump administration laid out a plan this year that would eventually allow cars to emit more pollution, automakers, the obvious winners from the proposal, balked. The changes, they said, went too far even for them.

But it turns out that there was a hidden beneficiary of the plan that was pushing for the changes all along: the nation’s oil industry.

In Congress, on Facebook and in statehouses nationwide, Marathon Petroleum, the country’s largest refiner, worked with powerful oil-industry groups and a conservative policy network financed by the billionaire industrialist Charles Koch to run a stealth campaign to roll back car emissions standards, a New York Times investigation has found.

The campaign’s main argument for significantly easing fuel efficiency standards — that the United States is so awash in oil it no longer needs to worry about energy conservation — clashed with decades of federal energy and environmental policy.

“With oil scarcity no longer a concern,” Americans should be given a “choice in vehicles that best fit their needs,” read a draft of a letter that Marathon helped to circulate to members of Congress over the summer. Official correspondence later sent to regulators by more than a dozen lawmakers included phrases or sentences from the industry talking points, and the Trump administration’s proposed rules incorporate similar logic.

While energy conservation is significant, the proposal says, the downside of additional petroleum consumption would be dwarfed by the rollback’s benefits.

Multipronged effort

The industry had reason to urge the rollback of higher fuel efficiency standards proposed by former President Barack Obama. A quarter of the world’s oil is used to power cars, and less-thirsty vehicles mean lower gasoline sales.

In recent months, Marathon Petroleum also teamed up with the American Legislative Exchange Council, a secretive policy group financed by corporations as well as the Koch network, to draft legislation for states supporting the industry’s position. Its proposed resolution, dated Sept. 18, describes current fuel-efficiency rules as “a relic of a disproven narrative of resource scarcity” and says “unelected bureaucrats” shouldn’t dictate the cars Americans drive.

A separate industry campaign on Facebook, covertly run by an oil-industry lobby representing Exxon Mobil, Chevron, Phillips 66 and other oil giants, urged people to write to regulators to support the rollback.

The Facebook ads linked to a website with a picture of a grinning Obama. It asked, “Would YOU buy a used car from this man?” The site appears to have been so effective that a quarter of the 12,000 public comments received by the Department of Transportation can be traced to the petition, according to a Times analysis.

Gary R. Heminger, Marathon’s chairman and chief executive, said in a statement that the company supported “sound fuel economy standards” and wanted to “help ensure they are achievable and based on existing technology.”

He added, “We appreciate the administration’s willingness to conduct a thorough review in order to ensure future standards are achievable and will actually benefit American consumers.”

A spokesman for Koch Industries, the energy conglomerate led by Koch, said the company had “a long, consistent track record of opposing all forms of corporate welfare, including all subsidies, mandates and other handouts that rig the system.”

The oil industry’s campaign illuminates why the rollbacks have gone further than the more modest changes automakers originally lobbied for.

Effect on automakers

The standards that the Trump administration seeks to weaken required automakers to roughly double the fuel economy of new cars, SUVs and pickup trucks by 2025. Instead, the Trump plan would freeze the standards at 2020 levels. Carmakers, for their part, had sought more flexibility in meeting the original 2025 standards, not a categorical rollback.

The Trump plan, if finalized, would increase greenhouse gas emissions in the United States by more than the amount many midsize countries put out in a year and reverse a major effort by the Obama administration to fight climate change.

The energy industry’s efforts also help explain the Trump administration’s confrontational stance toward California, which, under federal law, has a unique authority to write its own clean-air rules and to mandate more zero-emissions vehicles.

California has pledged to stick to the stricter standards, together with 13 other states that follow its lead. But President Donald Trump’s plan challenges California’s rule-writing power, setting up a legal battle that threatens to split the U.S. auto market in two.

That is a prospect automakers desperately want to avoid.

But for gasoline producers like Marathon, a shift toward more efficient vehicles poses a grave threat to the bottom line. In October, the company acquired a rival, Andeavor, making it the biggest U.S. refiner, with sales of 16 billion gallons of fuel a year.

Even while doubling down on gasoline, Marathon has projected an environmentally friendly public image. “We have invested billions of dollars to make our operations more energy efficient,” Marathon said in a recent report. The company’s Twitter account recently highlighted a gardening project and the creation of a duck pond at one of its refineries.

On a conference call with investors last week, Heminger, the Marathon chief executive, was already counting the extra barrels of fuel a Trump rollback would mean for the industry: 350,000 to 400,000 barrels of gasoline per day, he said.

“However, you have another side who doesn’t want to pivot away” from the stricter rules, Heminger said. “So we have a lot of work to do to keep this momentum going.”