Producing a gallon of ethanol gas from corn requires 95 percent less petroleum than producing a gallon from fossil fuels, a new study finds.

This method might also slightly reduce the production of greenhouse gases that speed up global warming, but the results on that point are not certain.

"It is better to use various inputs to grow corn and make ethanol and use that in your cars than it is to use the gasoline and fossil fuels directly," said Daniel Kammen of the University of California, Berkeley.

Ethanol could be even more energy efficient and 95 percent free of greenhouse gas emissions, Kammen said, if produced from woody plants instead of corn.

The study is detailed in the Jan. 27 issue of the journal Science.

Booze it up

Ethanol is produced by bacteria that ferment and break down carbohydrate sugars, such as the starch from corn. Humans have been fine-tuning this process for thousands of years, although mainly to brew alcoholic beverages.

The study refined results from several previous studies by comparing the total energy that goes into making ethanol gas from corn, such as harvesting and refining, and comparing it to the energy needed to produce gasoline from fossil fuels. Kammen's team looked into levels of greenhouse gases produced by both the production and the use of each fuel.

They found inconsistencies and errors in the previous work, which had suggested ethanol gas might not be beneficial.

After correcting the errors—which ranged from incorrect unit conversions to reliance on data from outdated methods more than a century old—the researchers arrived at a very different conclusion: not only does corn-based ethanol gas reduce petroleum use by 95 percent, it also reduces greenhouse gas emissions about 13 percent, although that decrease is within a range of uncertainty for the imprecise data involved.

"Making ethanol from corn is a good thing if you want to offset fossil fuels from overseas," Kammen told LiveScience. "On the greenhouse gas side of things, it is not clear if corn, as grown today, is a good thing. We just don't know yet, but it appears to be a mildly good thing."

A woody solution?

While corn-based ethanol is an improvement over gasoline, ethanol from woody, fibrous plants would pack even more energy. Willow trees, switch grass, farm waste and specially grown crops are all feasible sources.

The main energy components of these plants are cellulose and lignin, which produce more energy per unit—in the form of breaking hydrogen bonds—than the starches from corn.

"It looks to be that you can get just about twice the amount of energy by going the cellulose route, and greenhouse emissions are very small," Kammen said.

Assuming replant rates equal harvests, there is a 95 percent emission reduction from producing cellulosic ethanol over gasoline production in all three production phases—farming, refining, and use.

However, the real benefits of ethanol gas are not yet fully known, Kammen said, and the advantages could be even greater.

Wheels in motion

In the United States, some 5 million of the cars and trucks on the road are "flex-fuel," meaning that they can run either on traditional gasoline or E85, a mix of 85 percent ethanol and 15 percent gasoline.

Converting an automobile to run on flex-fuel costs about $100.

"This is actually one of the cheapest possible transitions you can make," Kammen said. "It cuts the cost of fuel by half at the pump."

However, there are very few pumps offering ethanol fuel. Despite the number of flex-fuel automobiles—California boasts more flex-fuel than diesel vehicles—ethanol-blended fuel accounted for only 2 percent of all fuel sold in the United States in 2004.

While it doesn't yet make sense to convert the entire economy to corn-based ethanol, Kammen said, improved methods for processing corn or using other ethanol-rich materials could drive such a change.

"The people who are saying ethanol is bad are just plain wrong," Kammen said.

Brazil has converted nearly all its cars and gas pumps to run on a 96 percent ethanol fuel produced from sugarcane. Brazilians have already seen the benefits of sugarcane fuel—not only is it cleaner burning, but since it is produced within the country, it is half the price of imported gasoline.

Kammen and his colleagues have made the previous studies, as well as their new model and data, available on the UC Berkeley Renewable and Appropriate Energy Laboratory website: http://rael.berkeley.edu/ebamm/.