"Pimentel found that one acre of U.S. corn field yields about 7,110 pounds of corn, which in turn produces 328 gallons of ethanol. Setting aside the environmental implications (which are substantial), the financial costs already begin to mount. To plant, grow, and harvest the corn takes about 140 gallons of fossil fuel and costs about $347 per acre. According to Pimentel's analysis, even before the corn is converted to ethanol, the feedstock alone costs $0.69 per gallon of ethanol.
More damning, however, is that converting corn to ethanol requires about 99,119 BTUs to make one gallon, which has 77,000 BTUs of available energy. So about 29 percent more energy is required to produce a gallon of ethanol than is stored in that gallon in the first place. 'That helps explain why fossil fuels (not ethanol) are used to produce ethanol,' Pimentel says. 'The growers and processors can't afford to burn ethanol to make ethanol. U.S. drivers couldn't afford it, either, if it weren't for government subsidies that artificially lower the price.' All told, a gallon of ethanol costs $2.24 to produce, compared to $0.63 for a gallon of gasoline.
So, if we were to switch entirely to ethanol use, we'd run out of petroleum four times as fast."