Ethanol

An alcohol-based fuel made by fermenting and distilling plant sugars, usually corn and grains. It can also be made from materials such as trees and grasses. Ethanol is typically blended with gasoline at a ratio of 85% ethanol, 15% gasoline--hence the term "E85" ethanol. E85 is only available in a few hundred filling stations in the U.S., but that number is increasing rapidly. Ethanol and flex fuel vehicles utilize ethanol.

Another type of ethanol, cellulosic ethanol, is made from sugars found in wood, certain waste products (corn cobs, underbrush, and sawdust), and grass. It's nicknamed "grassoline."

Pros and Cons: It's a clean burning renewable resource that will give your engine a power boost, but its low energy content hurts fuel efficiency (roughly 25% less efficient than gasoline) and requires a hefty amount of corn to produce.

Flex Fuel Vehicles

These "flexible" vehicles are designed to run on either conventional gasoline or E85 ethanol. A very eco-friendly option when using E85 fuel. Except for a few modifications to the engine and fuel system, they are identical to gas-only engines.

Pros and Cons: Dozens of flex fuel models are available, and unlike ethanol-only vehicles, drivers have a choice of E85 ethanol or gasoline. However, limited availability of ethanol pumps restricts potential.

Hydrogen

Hydrogen is the fuel source for internal combustion engines (ICE) and fuel cell vehicles (FCVs).When hydrogen reacts with oxygen, a chemical reaction occurs that creates electricity. Unlike electric vehicles that store energy in a battery, FCVs use hydrogen to create their own electricity. They're incredibly quiet and emit no emissions other than water vapor, which drips harmlessly from the tailpipe while electricity powers the vehicle.

Pros and Cons: Greenest vehicle you can buy. However, they're fragile, extremely expensive to produce and are limited by availability of filling stations.