When gasoline prices climbed to $3 a gallon last summer, hybrid vehicles--which combine a conventional engine and a battery-powered electric motor to achieve improved fuel economy and performance--began racing out of showrooms. Whereas the average U.S. car goes about 23 miles on a gallon of gas, a full-fledged hybrid car such as a Toyota Prius travels about twice as far on the same amount, depending on how it is driven. Annual U.S. sales of hybrids from 2004 to 2005 doubled to 200,000 and are expected to swell to more than half a million by 2010. By 2020 most new car models ought to offer a hybrid power-train option.

By then, next-generation technology, called plug-in hybrids, will offer motorists still better fuel efficiency as well as other perks: low-cost battery recharging overnight by simply connecting a 120-volt plug to an electrical outlet at home or work, very few trips to the gas station each year, and even the chance to sell surplus power back to the electric grid. Beyond the consumer benefits, the new plug-ins would help reduce the release of greenhouse gases by displacing emissions from millions of tailpipes to utility power plants. Today these facilities burn domestically supplied coal or natural gas, and in the future they should generate cleaner electricity from energy sources such as wind, solar or even advanced fossil fuel-based systems that capture carbon dioxide for underground storage.