What is it?
A biofuel refined from cellulose, the fibrous material that makes up most of the plant matter in wheat, switch grass, corn stalks, rice straw, and even wood chips.
What's good about it?
A lot. It's renewable and can be made from nonfood plants. It also has much greater "energy bounce" than gasoline or corn ethanol, which means it generates far more energy than it takes to produce. Greenhouse-gas emissions are lower than those from gas, too.
What's bad about it?
There are few expected downsides—except that the technology doesn't yet exist to mass-produce it. If cellulosic ethanol becomes a widespread fuel, it would be a boon for agricultural regions—while nations with little arable land would be left out.
Where would it be most useful?
Wherever it's available. Once it's produced, cellulosic ethanol will be the same as corn ethanol, fit for any flex-fuel vehicle capable of running on E85.
How much will it cost?
Unclear, because it's not mass-produced yet, but estimates suggest it would be considerably cheaper than gas on a per-mile basis—perhaps less than $1 per gallon.
When's it coming?
Five years, perhaps. It's not quite around the corner, but it's probably closer than hydrogen-powered cars. Backing by big companies like General Motors—and the possibility of technology breakthroughs—could speed adoption.
What's taking so long?
It's more difficult to break down the cellulose in plants than the starch that generates corn ethanol. Researchers are working on new enzymes and manufacturing processes to make it easier and cheaper to produce cellulosic ethanol.
Who's doing it?
Many small companies are producing it in labs, with the first large-scale plant set to start running this year. Venture capitalists are interested, while General Motors and other automakers may also invest in companies producing this fuel.
Could it be a silver bullet?
Maybe half a bullet. It's renewable, would cut greenhouse gas emissions, and ought to be affordable—if the technology develops. It still generates some pollution but far less than oil-based fuels do.