What would it take to get you into a diesel-engine car? Will you wait till diesels run clean, and there's no engine clatter? Until somebody makes diesel airplane engines? Until a diesel-engine car wins an auto race? Done, done, and done.

In March, an Audi won the Sebring 12 Hours endurance race, four laps ahead of the gasoline-powered runner-up. And technology has eliminated the noise of diesel engines; there's none inside the car and hardly any outside. A sophisticated common rail fuel-injection system propels an atomized stream of fuel into the cylinders at twice the speed of sound, ensuring that air and fuel are properly mixed. They start almost instantly, even in the cold.

As for running clean, this year the EPA ordered fuel companies to stop whining and start refining diesel fuel with low levels of sulfur, the pollutant that's responsible for the rotten-egg smell and black soot. Most diesels also run on biodiesel, fuels in part made from vegetable oils or animal fats. So if the Jetta ahead of you smells like a McDonald's, now you know why. New technologies, such as particulate filters (here now) and the injection of urea into the exhaust stream (coming), make diesels even cleaner.

In European countries, Herr Doktor Rudolf Diesel's 1892 invention purrs along under the hoods of one-third to two-thirds of all cars. But here in the U.S., only a dozen passenger-vehicle models with diesel engines are offered: a bunch of brawny American trucks/SUVs, the Mercedes-Benz E-Class, and four Volkswagens. California, Maine, Massachusetts, New York and Vermont effectively outlaw diesels, and some automakers say they won't introduce diesel cars until they're allowed in every state.

Still, I don't think you can deny that we're entering a golden era of performance coming from a wider array of engine types: gasoline or diesel boosted by hybrid, turbocharged, or supercharged technologies. If you're a stop-and-go driver, hybrids make sense. But if you rack up a lot of highway miles and/or spend a lot of time idling, a diesel may be your best bet. Wait a year and you'll see more choices. Diesels are definitely back.