The Obama administration is considering a fleetwide average of 56.2 miles per gallon for all new cars and trucks sold in the U.S. by 2025, two people briefed on the matter said.

The proposal would roughly double current fuel-economy targets, and would likely raise the price of some cars by several thousand dollars.

The proposal isn’t final, and could be adjusted over the next several weeks as regulators prepare a formal draft to send to White House budget officials.

U.S officials presented the proposal to representatives of Detroit auto makers this week to determine the costs of such a proposal, said one of the people briefed on the matter. This person emphasized that the 56.2 mpg figure was floated as a means to kick negotiations among California, environmental groups and the auto industry into the final phase, and that the numbers could change.

The administration has said previously that it is looking at requiring cars average between 47 and 62 mpg by 2025.

The fuel-mileage targets would be accompanied by stringent rules to reduce vehicle emissions of greenhouse gases.

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