Bentley's first biofuel car, scheduled to debut at the Geneva auto show next week, will be a powerful two-seater called the Continental Supersports.

Its 6-liter W12 twin-turbocharged engine delivers 621 hp, goes from 0 to 60 mph in 3.7 seconds and has a top speed of 204 mph.

ENLARGE Bentley Continental Supersports

It's also the first Bentley capable of running on both gasoline and E85 biofuel or any combination of the two, a technology knows as FlexFuel. Bentley says the Supersports is stage one of its commitment announced in Geneva last year to make the entire Bentley lineup capable of running on renewable fuel by 2012.

Bentley says a new Fuel Quality Sensor in the Supersports' fuel supply circuit detects the current mix of gasoline and bioethanol in real time.

"The W12 has been re-engineered to run on petrol or a mix of petrol and bioethanol," Brian Gush, director of Bentley chassis and powertrain engineering, said in a release. "A sophisticated fuel sensing system ensures that power and torque remain constant irrespective of the fuel ratio to deliver seamless power delivery in the Bentley tradition."

Bentley claims E85 biofuel offers up to 70 percent reduction in carbon emissions on a "well-to-wheel" basis. Rather than just tailpipe emissions, well-to-wheel quantifies how much carbon a fuel emits from its growth or extraction to its combustion or deployment, including refinement, distillation and transport of the fuel.

The Supersports will go on sale worldwide this fall, but FlexFuel models won't arrive in North America until the summer of 2010, following regulatory approval.