Carmakers with diesel models had to hit the pause button on U.S. sales in 2007. New clean-air standards that took effect in January forced them to retool their diesels to reduce particulates, or soot, and nitrous oxides, which contribute to smog.

But in 2008, a number of new diesels will join the handful now on the market. Most of the models will be from Audi, BMW, Mercedes-Benz and Volkswagen — automakers based in Europe, where half of the vehicles sold are diesels.

But Chrysler, GM, Honda and other Japanese carmakers also have plans to offer light-vehicle diesels. The new models should meet even the strict emissions standards imposed by California and four northeastern states, which currently ban diesel sales.

New-generation clean diesels aren't nearly as dirty, noisy or unreliable as the cars many people remember from a generation ago. Although it's made from petroleum, diesel is an easy way to ease oil-shortage and climate-change concerns. Diesel engines get 30 percent better fuel economy than comparable gasoline engines, and they emit far fewer greenhouse gases. Another bonus: Diesel engines can run on biofuels made from vegetable oils.

The price premium for diesels is less than it is for hybrids. For example, the Mercedes E320 diesel sedan costs only $1,000 more than the gas-engine E350 — a premium easily recouped through lower fuel costs. That gap could widen slightly as carmakers refine their emissions-cleanup systems.

• The ethanol problem. Despite the hype from Detroit automakers, ethanol won't cure our addiction to oil — at least not anytime soon. Ethanol is made from corn, so it's renewable, homegrown and is responsible for fewer greenhouse gases than petroleum is.

Sold as E85 (85 percent ethanol and 15 percent gasoline), it already fuels the five-million-plus "flex fuel" vehicles on the road. Those flex-fuel vehicles cost a bit more to build, but carmakers aren't passing along the extra cost.

But ethanol contains less energy than gasoline, and therefore delivers lower fuel economy. Plus, even if every acre of corn grown in the United States were used to make ethanol, it would meet only 12 percent of domestic fuel needs, according to one study by University of Minnesota researchers.

Currently, E85 is available at fewer than 1,300 filling stations, most of which are in the Midwest. It costs more to produce than gasoline — when it's cheaper than gas, the retailer is passing along savings from credits available to the producer. E85 will be a more viable substitute for gasoline when it becomes cost-effective to turn wood chips, cornstalks and even prairie grass into ethanol.