Besides, there's much to be done to improve the combustion engine, engineers from Bentley, BMW and Porsche say, either through increasing its efficiency or developing alternative fuels. Bentley developed the flex-fuel-capable, $245,000 Continental Supersports coupe for that very reason.

"We believe bioethanol is a really good alternative to reducing CO2 emissions," says Brian Gush, Bentley's director of chassis and powertrain engineering. "This is a renewable source, which will be growing into the future."

by 2012 at least half the cars being built will be flexfuel.