The Trump administration has relaxed controls on America's oil reserves in a move that makes no mention of climate change.
A memo published online with little publicity appears to undermine decades of government campaigns promoting fuel-efficient cars.
The new government position follows a decade of fracking, which has unlocked shale oil reserves.
That gives the US "more flexibility than in the past to use our oil resources with less concern", the Energy Department memo said.
The growth of natural gas and other alternatives to petrol have also reduced the need to import oil, which "in turn affects the need of the nation to conserve energy", the memo added.
Donald Trump has queried the existence of climate change and called for an easing of regulation on the oil, gas and coal industries, including repealing President Obama's Clean Power Plan.
Vehicles are the biggest source of climate change emissions in the US, overtaking power generation last year.
Mr Trump's administration is proposing freezing mile-per-gallon targets for cars and light trucks after 2020, instead of continuing to make them tougher.
That could increase US oil consumption by 500,000 barrels a day, the administration has said.
The move is short-sighted, according to an analyst from the Oil Price Information Service.
"It's like saying 'I'm a big old fat guy, and food prices have dropped – it's time to start eating again,'" said Tom Kloza.
"If you look at it from the other end, if you do believe that fossil fuels do some sort of damage to the atmosphere… you come up with a different viewpoint. There's a downside to living large."
A lawyer for the Environmental Defence Fund, Sean Donahue, said climate change was a "clear and present and increasing danger".
Senator Tom Carper, a Democrat from Delaware, said: "American businesses, consumers and our environment are all the losers under his plan.
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"The only clear winner is the oil industry. It's not hard to see whose side President Trump is on."
The Energy Department said it still believed in the need to "use energy wisely".