Alternative fuels aren't a perfect alternative to gasoline. They have less energy than gas and cost more; it's improbable that production will be ramped up for more than a fraction of America's vehicles; they have corrosive effects on normal fuel systems; and it's not certain we'll get the technology to work soon.

Popular Mechanics (May) calculated the cost of driving a small car coast to coast on various fuel sources: It ranged from $60, for an all-electric car using coal-fired powerplants to generate power, to $804, using hydrogen. Gasoline was pegged at $231 for the trip, although the run-up in prices since the article was written would bring the cost to around $275.

Ethanol, or grain alcohol, is the special ingredient in gasohol (10 percent ethanol, 90 percent gasoline) and E85 (85 percent ethanol, 15 percent gasoline). It's derived from fermenting corn, apples, or sugar cane (maybe Fidel has held on so long by selling black-market E85?) and it's also how you make moonshine. Ethanol fuel mixtures burn cleaner than gasoline, and there are about 6 million flexible fuel vehicles (FFVs) in the U.S.

Natural gas runs cleaner than gasoline, and when compressed, may have more energy (on a volume basis). It's also cheaper than gasoline, especially since there are no motor fuel taxes. However, scrubbing the methane out of natural gas and compressing it to 3,000-plus pounds per square inch takes energy—about 2 kilowatt hours (20 cents' worth) for the equivalent of a gallon of gas. And though the U.S. has lots of natural gas, much of it is already spoken for.

Biodiesel uses vegetable oil, rendered chicken fat, or old deep-fryer oil in place of petroleum diesel fuel, yet yields the same energy content. It costs more and often gels at outside temperatures unless it's kept warm in the storage tank and in the vehicle. Biodiesel can be mixed with regular diesel and burns a bit cleaner. There's little downside, other than needing a diesel engine, living with higher costs than petroleum diesel (pure B100 is about $3.50 a gallon), and if you're riding behind a biodiesel vehicle burning fryer oil, that fast-food smell.

Electricity was around before hybrid gas-electric vehicles, it's affordable (about 2 cents a mile), and it creates less pollution, even if it comes from coal-fired plants. But the range of an electric-power car is limited to about 100 to 120 miles per charge. And as Toyota noted in a recent technology seminar , rechargeable batteries don't last as long if they're fully charged and fully discharged. In comparison, Toyota says, if you operate a battery only in the middle 60 percent of its charge range, they'll last the life of the car. That's fine for hybrids using battery-power electric motors as boosters, but it would effectively cut the range of an all-electric vehicle to 60 to 75 miles.

Hydrogen as a combustion fuel won't be a serious alternative for at least a decade. The electrolysis conversion process used to produce hydrogen isn't cheap; and hydrogen needs to be compressed, like natural gas, or liquefied, to provide reasonable range. Even with these setbacks, BMW says it will have a limited-production version of its luxury 7 Series running on hydrogen within two years.

Diesel, like gasoline, comes from petroleum, and it's popular in Europe. You can refine different ratios of diesel and gasoline from the same barrel of oil, but it involves massive reinvestment. A gallon of diesel has about 10 percent more energy than gasoline and extracts even more power than that, because it's compressed more in the engine. But it has two pollution problems: particulates and nitrous oxides (NOX).

The particulates (you see them as soot from ill-tuned diesels) can be controlled by filters, and NOX can be reduced through ultra-low-sulfur fuels, mandated in the U.S. as of June 1. (Europe isn't as strict on these emissions, and diesel is often taxed less.) Even with low-sulfur fuel, California and four other states have tighter emissions rules that make passenger-car diesels unlikely until 2008. Some automakers have said they won't introduce diesels until they can be sold in all 50 states. But Mercedes-Benz will forge ahead in the U.S. with an ultra-clean diesel technology called BlueTec, and Honda announced a diesel-engine passenger car for the U.S.

To read more about Bluetec and other new car technologies, click here.

Alternative fuel sounds good when you listen to its proponents. But what's practical for an energy-conscious fraction of the population may not work for all 200 million vehicles in the U.S. The soundest alternative-fuel policy may be to buy cars that don't burn as much fuel, no matter what type it is.