GAS-ELECTRIC HYBRIDS

Japanese automakers have led in developing hybrids that shift back and forth between battery and gas power, getting 60 miles per gallon or more. The battery recharges when the driver hits the brakes. Honda put the first hybrid on U.S. roads -- its Insight -- in 1999. Toyota has a backlog of orders for its hybrid Prius and plans to steadily expand until it's making 1 million hybrid vehicles in 2010, spokeswoman Martha Voss said.

Ford Motor Co. Chairman Bill Ford pledged to put 250,000 hybrids on the market by 2010 -- a tenfold increase.

DaimlerChrysler is selling hybrid buses.

Under the new energy law, early hybrid buyers can get federal tax credits of as much as $3,000 -- roughly the added cost.

ETHANOL

Clean-burning ethanol, made from cornstarch, powers nearly all of Brazil's vehicles. U.S. ethanol production has soared to 4 billion gallons a year -- there are more than 90 plants -- enough to offset about 1 percent of the petroleum that America uses.

The new energy law requires a doubling of ethanol production by 2012, but Minnesota is the only state that requires gasoline to contain at least 10 percent ethanol (and 20 percent by 2013).

High ethanol blends can be used only in flexible-fuel vehicles, still a small percentage of cars on the road. And ethanol plants burn a finite resource -- natural gas -- to produce it.

PLUG-IN HYBRIDS

New, high-powered phosphate lithium ion batteries can power hybrids for as much as 60 miles before the gas engine takes over. Car owners can "plug in" battery chargers overnight. Commuters could get more than 100 miles to a gallon of gas, and those using an 85 percent ethanol blend in their tanks could get 500 miles to a gallon of petroleum.

Most major automakers are taking a wait-and-see posture toward plug-ins, though Chrysler-Daimler is experimenting with a plug-in Sprinter van with a 20- to 30-mile battery range. It would cost an extra $3,000 to $5,000.

EnergyCS of Monrovia, Calif., says its retrofitted hybrids have a 60-mile battery range. Conversion kits would cost $10,000 to $12,000.

DIESEL

Europeans have dramatically improved fuel efficiency by buying diesel-powered cars, made by DaimlerChrysler and other automakers, that get as much as 70 mpg. These engines burn far cleaner than the diesels that polluted the air with carbon dioxide in the 1970s.

Except for pickup trucks, diesel vehicles have yet to catch on in the United States. Allen Schaeffer, executive director of the Diesel Technology Forum, said a diesel option pickup costs about $5,000 extra, but diesel cars cost only $350 to $1,000 more. Early diesel buyers also are eligible for tax credits of as much as $3,000.

One problem: Diesel comes from crude oil, so its use is seen only as a conservation measure. A solution: Plants have begun making bio-diesel from soybean oil and animal fats.

HYDROGEN

In his 2003 State of the Union address, President Bush pushed for the development of pollution-free hydrogen fuel cell vehicles that could be "the first car driven by a child born today."

Honda, General Motors and other carmakers have developed experimental fuel cell models, but there are challenges, such as how to store enough of the volatile gas for a car to travel 300 miles without refueling.

Other problems: Extracting hydrogen from natural gas would tap a needed resource; removing it from water is a scientific challenge.

Energy Department officials say the hydrogen option won't be viable before 2020.

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