Being a professional car-tester, which is to say a person who gets asked for unpaid car-buying advice practically every day, I know these distinctions have already been lost on many car buyers. And I fear they're well on their way to being lost on our governments, too.

Lately, right-minded people have been calling me and telling me they're thinking about buying the Lexus 400H, a new hybrid S.U.V. When I tell them that they'd get better mileage in some conventional S.U.V.'s, and even better mileage with a passenger car, they protest, "But it's a hybrid!" I remind them that the 21 miles per gallon I saw while driving the Lexus is not particularly brilliant, efficiency-wise -- hybrid or not. Because the Lexus 400H is a relatively heavy car and because its electric motor is deployed to provide speed more than efficiency, it will never be a mileage champ.

The car that started the hybrid craze, the Toyota Prius, is lauded for squeezing 40 or more miles out of a gallon of gas, and it really can. But only when it's being driven around town, where its electric motor does its best and most active work. On a cross-country excursion in a Prius, the staff of Automobile Magazine discovered mileage plummeted on the Interstate. In fact, the car's computer, which controls the engine and the motor, allowing them to run together or separately, was programmed to direct the Prius to spend most of its highway time running on gasoline because at higher speeds the batteries quickly get exhausted. Indeed, the gasoline engine worked so hard that we calculated we might have used less fuel on our journey if we had been driving Toyota's conventionally powered, similarly sized Corolla -- which costs thousands less. For the owner who does the majority of her driving on the highway, the Prius's potential for fuel economy will never be realized and its price premium never recovered.

For years, most of the world's big car makers have shied away from building hybrids because while they are technologically intriguing, they are also an inelegant engineering solution -- the use of two energy sources assures extra weight, extra complexity and extra expense (as much as $6,000 more per car.) The hybrid car's electric battery packs rob space from passengers and cargo and although they can be recycled, not every owner can be counted on to do the right thing at the end of their vehicle's service life. And an unrecycled hybrid battery pack, which weighs more than 100 pounds, poses a major environmental hazard.

So the ideal hybrid car is one that is used in town and carefully disposed of at the end of its days. Hybrid taxis and buses make enormous sense. But the market knows no such distinctions. People think they want hybrids and they'll buy them, even if a conventional car would make more sense for their pocketbook and for the environment. The danger is that the automakers will co-opt the hybrids' green mantle and, with the help of a government looking to bail out its troubled friends in Detroit, misguidedly encourage the sale of hybrids without reference to their actual effect on oil consumption.