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Energy analysts said ethanol reduces some oil use. But there have been conflicting studies about whether more energy is used to grow corn and produce ethanol than it provides as a fuel. Electricity — typically produced from natural gas or coal — is needed to operate ethanol plants, for instance, and farm equipment uses petroleum products.
Tad W. Patzek, a professor of geo-engineering at the University of California at Berkeley, said ethanol production uses far more energy than making gasoline and releases more greenhouse gases, which have been linked to global warming. He co-authored a study last year that said corn ethanol requires 29 percent more energy to make than it produces.
The industry disputes Patzek's conclusions, saying the making of ethanol is cleaner and more environmentally friendly than gasoline production.
Environmentalists have not been sold on ethanol. "The greatest thing to recommend it is that it's not gasoline," said David Hamilton, director of the Sierra Club's global warming and energy program. "What is oil dependence worth versus a very high amount of energy it takes to make?" Still, he said cellulosic ethanol holds more promise than corn-based ethanol.