General Motors has unveiled a prototype fuel cell car, the Sequel. Unlike previous fuel cell prototypes, the Sequel has the acceleration of a commercial car and can travel 300 miles before refueling, making it the first hydrogen prototype that can go as far between fill-ups as a conventional car because of a system of compressed hydrogen.

The drawback is the price. Carlos Ghosn, Nissan's chief executive, said that "today a fuel cell car probably costs about - I'm going to be optimistic - $700,000." He added, "We're far from sticker price, eh?"

Environmentalists are skeptical. While G.M. says it will theoretically be able to mass-produce fuel cell vehicles affordably by 2010 - even though most competitors, which are also working on the technology, say it will be decades before such vehicles are viable. Meanwhile, for the 2003 model year, the average fuel economy of G.M.'s cars and trucks fell to its lowest point in two decades. For all auto makers, but the fuel economy of the average vehicle has declined - to 20.7 miles a gallon in the 2003 model year from 22.1 in 1988. And GM has lobbied vigorously to block more stringent fuel regulations and has taken major roles in lawsuits against California's antipollution rules.

Fuel cells remain problematic, especially if peak oil appears within the next few years.