In addition, the jury still seems to be out on ethanol's effect on the environment. A much-cited study released this year by the University of California at Berkeley concluded that ethanol, in its production and use, generally produces about as much greenhouse emissions as gasoline, and in a best-case scenario only up to 15 percent less. More environmentally friendly production plants could improve this profile, but the Berkeley study has been fuel for ethanol's critics.

Then there's the matter of a limited planetary surface.

Getting enough farmland to feed a growing appetite for fuel is no small feat. Competition for land between ethanol-intended corn and edible crops could conceivably drive food prices higher. Regarding Brazil's energy miracle, environmentalists are worried that pressure for land will lead to further clearing of the Amazon rain forest.

Such concerns over land are even more pronounced in the United States. Corn is not as sweet as sugarcane, which means corn burns off less energy. As a result, Brazil's ethanol has eight times as much energy as any corn-based variety.

That means more raw material is needed to achieve the same results. Pimentel's study found that, in the U.S., an estimated 11 acres are needed to grow enough corn to fuel one vehicle for one year.

How much land is that for all of us, exactly? If, hypothetically, all U.S. cars ran on 100 percent corn-ethanol, and if Pimentel's analysis is correct, then 97 percent of the entire country's land area -- including real estate now occupied by cities -- would be needed to grow corn.

Organic in Your Tank

Is it possible for ethanol to be a viable solution without threatening to make corn into The Crop That Ate All Land? Benjamin Franklin might have had the answer: "Waste not, want not."

Ethanol can be made from any organic material that contains sugar, such as sugarcane or sugar beets, or that contains starch or cellulose that can be converted to sugar, such as corn. Barley, soybeans, or wheat could also be used. In France, ethanol is made from sugar beets -- and, unsurprisingly, from low-grade wine.

But organic leftovers can also be used. For example, Coors Beer is brewing 1.5 million gallons of ethanol fuel each year from wasted material -- offering future alternative meanings for the term "getting wasted."

The fibrous content of plants -- the stalks, the leaves -- or other organic material, such as prairie grass, switch grass, or willow trees, or even industrial organic waste such as sawdust or paper pulp, can produce ethanol. Making this kind of "cellulosic ethanol" could reduce the price of fuel, increase energy efficiency, decrease greenhouse gas emissions -- as much as 80 percent over gasoline -- and reduce the need for farmland. (continued...)

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