Corn is just one of the many raw materials, or feedstocks, that can be converted into ethanol and used for fuel. As of 2010, 187 facilities in the United States were producing ethanol, most of them using corn as feedstock [source: Renewable Fuels Association]. Corn ethanol can cut greenhouse gas emissions, but because it contains less energy than gas, a vehicle running on this biofuel would get significantly lower mileage than one running on gasoline. Producing corn ethanol on a large scale could also create a shortage of corn for food. Corn ethanol is also criticized for creating undesirable environmental effects. Opponents of corn ethanol fuel (and other biofuels as well) argue that when areas such as grasslands and rainforests are converted to provide land to grow corn, the overall result is an increase in greenhouse gas emissions [source: The Nature Conservancy]. And the processing corn into ethanol actually uses a huge amount of fossil fuel. Still, many producers are banking on corn: Currently, about a third of all corn grown in the United States is used to make fuel [source: The New York Times].