Flex Fuel

The Flex Fuel logo on a Ford Fusion car parked on the lot at the Serramonte Ford dealership in Colma, Calif.

David Paul Morris/Getty Images

This technology, which allows a driver to choose between regular gasoline or an ethanol blend, has been around for a while. Ethanol blends are designated by the letter E followed by a number; E85 means the fuel is 85 percent ethanol and 15 percent gasoline. The Flex Fuel badge usually means the vehicle can use up to E85, as well as lower-percentage blends like E10.

Often, you'll find that Flex Fuel vehicles are big trucks and SUVs that drink fuel like a fish drinks water. Ethanol has a higher octane rating, but you get fewer miles per gallon when using it. On the plus side, ethanol can be made from biological sources.

But for expensive performance cars, that's the perfect mix. Bentley Motors is working to make its entire fleet of cars Flex Fuel-capable, beginning with the Bentley Continental SuperSports, the fastest Bentley ever built.

The engineers at Swedish supercar company Koenigsegg used ethanol to boost both power and green credentials. The company's very limited edition CCXR model had an 806 horsepower engine -- when it was powered by gasoline. But fill the tank with higher-octane ethanol, and the engine could crank out an amazing 1,018 horsepower.