Greenhouse-gas emission standards will become more stringent with each new model year from 2012 to 2016. The new regulations include an industry-specific emissions-trading scheme under which car makers that don't meet the new standards can buy credits from rivals that have exceeded the standards.

The efficiency gains in autos sold under these standards will save 1.8 billion barrels of oil over the life of the program. This is the first time the US Clean Air Act has been used to tackle global warming emissions, and is also the first significant increase in fuel economy standards since the original 1975 standards.

"These standards are a grand slam: billions of dollars in consumer savings at the pump, a huge reduction in oil use, significant cuts in pollution, and they will help a more sustainable domestic auto industry thrive," states Michael Brune, Sierra Club Executive Director.