Wagoner said GM believes in the ultimate "electrification" of the automobile to help "improve energy diversity and minimize the automobile's impact on the environment." As GM sees it, the electricity can come from a battery, an engine-assisted electric drive or, further out, a hydrogen fuel cell. The key point is that electricity should one day replace petroleum as the universal energy source.

PHVs basically work like conventional gasoline/electric vehicles such as the Toyota Prius, but use larger batteries to allow driving longer distances without using the gas engine. The battery recharges while driving, as in other hybrids, but can also be plugged in, preferably overnight when electric rates are lowest. Some private entrepreneurs have already built experimental PHVs, as the concept promises better fuel economy and lower emissions versus conventional hybrids. GM says batteries don't yet exist for plug-ins to be practical or affordable for mass sale, but says it's working with battery makers to speed the day.

Meantime, GM says it will keep promoting bi-fuel engines using gasoline/E85 ethanol, as well as "clean diesel" engines for heavy-duty trucks. The company will also offer more regular hybrid vehicles with the "two-mode" system it developed with DaimlerChrysler and BMW. That uses a special transmission with four gears and two "continuously variable modes," a 3.6-liter gasoline engine, and a nickel-metal-hydride battery pack to run a pair of "active cooled" permanent-magnet motors. As with other hybrids, this system uses gasoline and/or electric power depending on driving needs; recharges the battery with regenerative braking; and cuts off the engine when the vehicle is stopped to save fuel and reduce emissions. GM claims the two-mode system is suitable for a wider variety of vehicles and engines, as it fits into the same space as a conventional automatic transmission.