Corn Ethanol

A fuel derived from the sugars in corn and other plants. Pure ethanol is usually blended with gasoline.

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What is it?

A fuel derived from the sugars in corn and other plants. Pure ethanol is usually blended with gasoline. "E10"—10 percent ethanol—is common today. E85—85 percent ethanol—is the highest practical blend; some gas is still required for combustion in most climates.

What's good about it?

It's renewable, and corn is plentiful in the United States. Burning corn ethanol can cut greenhouse-gas emissions by as much as 20 percent, compared with gasoline. Producing ethanol generates fewer emissions, too.

What's bad about it?

It contains one third less energy than gas, which means mileage is 30 to 40 percent lower. Massive ethanol production could cause a shortage of corn available for food and destroy habitat. It could also increase smog in urban areas.

Where would it be most useful?

Mild blends are widely available. But E85—85 percent ethanol, 15 percent gas—is found only at about 1,500 filling stations in the United States., mostly in the Midwest. That number will grow, since the 2007 energy law mandates a fourfold increase in ethanol production by 2022.

How much will it cost?

It's often a bit cheaper than gas—but not a bargain, since mileage is lower. At $2.50 per gallon, for instance, it takes about $3.30 worth of E85 to drive the same distance as a gallon of $3 gas. Cars must also be specially outfitted to run on E85.

When's it coming?

Ethanol has been around for many years but hasn't caught on because the fuel isn't widely available, and for most drivers it's more expensive on a per-mile basis. Virtually all cars can run on mild blends like E10, and most automakers build E85-capable cars or plan to.

What's taking so long?

In some farm states, where the corn is grown, there are plenty of ethanol stations. But there are no pipelines from there to major population centers, and the fuel hasn't caught on nationwide because it doesn't really save drivers money.

Who's doing it?

General Motors, Ford, and Chrysler build the most "flex-fuel vehicles," able to run on gas or any ethanol blend up to E85. Converting new cars to FFVs on the assembly line costs less than $100; third-party shops can convert existing cars for $1,500 or less.

Could it be a silver bullet?

Highly unlikely. Corn ethanol helps reduce greenhouse gases and is a renewable energy source. But it's a less potent form of energy than gasoline—and doesn't really save drivers money, at current prices.