Vehicle manufacturers and environmental groups have backed a landmark deal by US lawmakers to tighten the fuel-economy standard for cars.
Under the agreement, hammered out by Democratic leaders in Congress, carmakers will be required to achieve an average for all light vehicles of 35 miles per gallon by 2020.
In a key concession to the industry, the new target is an average rather than an absolute requirement for passenger cars and light trucks, which include sports utility vehicles (SUVs).
The current standard for Corporate Average Fuel Economy (Cafe) is 27.5mpg for cars and 22.2mpg for trucks. The truck standard was raised last year, but the Detroit carmakers and their allies have, until now, resisted attempts to tighten Cafe rules for cars, maintaining that such a move would significantly increase vehicle prices while encouraging use of lighter materials - thus compromising safety.
However, the recent drive to lower US dependence on foreign oil has heightened consumers' interest in fuel-efficient vehicles, and the auto industry's diminished clout on Capitol Hill has put the carmakers on the defensive.
Nancy Pelosi, the speaker of the US House of Representatives, has forcefully supported tighter rules.
Phyllis Cuttino, director of the Pew Charitable Trusts Campaign for Fuel Efficiency, said: "If the house and senate finally approve this deal and the president signs it, they will all have done more for consumers at the pump than any congress or administration since the 1970s."
Rick Wagoner, chief executive of General Motors, said the new rules posed "a significant technical and economic challenge to the industry".
GM would seek to achieve the goals "with an array of engineering, research and development resources".
GM and its rivals are working on petrol-efficient technologies, including electric, diesel and fuel-cell vehicles. Under the new rules, carmakers will receive Cafe credits for vehicles running on biofuels.
Industry critics have long maintained that the carmakers already have or will soon have the technology to improve significantly their vehicles' fuel consumption.
Complying with the new rules could be easier if Americans continue their trend of buying fewer pick-up trucks and SUVs, and more small cars and crossover utility vehicles, which are more fuel-efficient.
George Pipas, a Ford Motor sales analyst said crossovers were likely to outsell traditional SUVs this year for the second year running.
The Cafe deal is part of a wider energy bill before Congress. Agreement has yet to be reached on other key provisions.
But one possibility is that the fuel-economy measures could be put on the statute book without agreement on the rest of the energy bill.