Hybrids

PROS - Potential for excellent fuel economy, run on existing gasoline supplies, and drive just like regular cars, requiring no behavioral change.

CONS - Some hybrids cost much more than similar conventional cars. Some don't live up to the gas mileage buyers may expect, especially for the price premium.


Plug-in hybrids

PROS - Up to 40-mile all-electric range, home recharging infrastructure available, gas engine can extend range for long trips, claimed fuel economy can exceed 100 mpg, cheaper per-mile cost, no emissions when running in electric mode.

CONS - Expensive additional batteries elevate production cost, daytime recharging could strain electric grid, requires plugging in to reap the benefit.


Ethanol

PROS - Domestically produced from corn, or someday a wide variety of waste materials, 10-percent blends (called E10) can be burned in any new car. Over 5 million cars can use E85.

CONS - Cars get about 25 percent lower fuel economy running on E85 than gasoline, less than 1 percent of U.S. gas stations carry E85, federal fuel economy credits awarded to automakers for E85 cars lower overall fuel economy for all cars, ethanol made from any food crop can adversely affect food prices. Farm equipment involved in crop production runs on petroleum limiting the net benefits.


Compressed natural gas

PROS - Costs much less than gasoline, burns much cleaner, provides comparable power.

CONS - Huge gas tanks reduce trunk space and carry the equivalent of only a few gallons of gasoline, limited range, few places for consumers to refuel in most of the country, plus refueling can be very slow.


Diesel/biodiesel

PROS - Thirty percent better fuel economy than an equivalent gasoline vehicle, widely available, lower cost premium than for hybrid vehicles, engines deliver lots of torque for a given displacement, and any diesel car can run on a blend of renewable biodiesel fuel. (A 5-percent blend is typical.) With effort and investment, diesel engines can be converted to run on pure waste vegetable oil.

CONS - Traditionally more engine noise and vibration. Currently higher cost of diesel can cut into gas savings. Some clean diesels require refills of urea solution.


Hydrogen fuel cells

PROS - No emissions other than benign water vapor, equivalent fuel economy about twice that of gasoline vehicles. Hydrogen is abundant and some of it can be made from renewable energy.

CONS - Fuel cells are expensive, durability is limited, acceptable range requires extremely-high-pressure on-board hydrogen storage, few places to refuel, hydrogen is very expensive to transport, no infrastructure in place yet. Currently hydrogen fuel is made from nonrenewable natural gas.


Battery electric vehicles

PROS - No emissions from the car, cost per mile a fraction of gasoline-powered car, universally available recharging infrastructure, electricity can be partially derived from renewable sources, instant torque from electric motor.

CONS - Long recharging times, limited range, expensive batteries, electricity production in much of the country uses coal-not a clean-burning source.