The 918 Spyder is expected to cost around $600,000--several times as much as Tesla Motors's $109,000 2010 Roadster. But Porsche is also experimenting with all-electric versions of its entry-level Boxster as well. Industry analyst Rebecca Lindland of IHS Automotive says that high-performance hybrids from Porsche, as well as those from Audi and Mercedes-Benz, could pose a challenge to startup electric-vehicle makers.

"This puts tremendous pressure on Tesla and Fisker," Lindland says. "They're well-established carmakers with a lot of resources who are suddenly coming in to play in Tesla's very elite sandbox."

More broadly, Lindland says, cars like the 918 Spyder show how committed previously skeptical automakers are to dealing with tighter limits on carbon-dioxide emissions and fuel-efficiency requirements.

Mike Omotoso, manager of the power train forecasting group at J.D. Power and Associates, says that some of the technology in Porsche's 918 Spyder could eventually find its way into other vehicles made by Porsche. It might also end up in cars made by Volkswagen, which owns a controlling interest in Porsche.

Despite its power, Porsche says the 918 Spyder is rated at the equivalent of 78 miles per gallon using European test cycles. As the EPA is learning with the 2011 Chevy Volt range-extended electric vehicle, however, it's a substantial challenge to provide useful information on a vehicle's fuel consumption when it depends so much on how it's used.

Porsche's first production hybrid vehicle, the 2011 Porsche Cayenne S Hybrid, is now reaching dealers in the U.S. and Europe. The company is also developing the 911 GT3 R Hybrid, a racing car that stores recaptured energy not in a battery but in a flywheel system.