How many acres of corn would have to be planted to replace all U.S. gasoline consumption with ethanol?

U.S. gasoline consumption was 134 billion gallons in 2003.
The USDA says that each bushel of corn is now producing about 2.7 gallons of fuel, and U.S. corn crops have averaged 138 bushels per acre over the past decade, for an average per-acre yield of about 375 gallons of ethanol.
Thus, if ethanol and gasoline had the same energy content per unit volume, replacing all U.S. gasoline consumption with ethanol would require 357 million acres of cropland.
However, the energy content of ethanol is lower than that of gasoline. Gasoline contains about 115,000 Btu’s/gallon, compared to ethanol’s 76,000 Btu’s/gallon–in other words, ethanol yields about 35 percent less energy per gallon than gasoline.
Therefore, to replace gasoline with ethanol, about 482 million acres would have to be planted with corn. That exceeds total U.S. cropland for all food and fiber, which was 434 million acres in 2002.
Actually, significantly more than 482 million acres would be required, because it takes fossil energy, including petroleum, to produce and supply ethanol. According to the USDA’s Dr. Hosein Shapouri, the net energy gain in corn ethanol is 25% (later increased to 34% using unexplained math).
Taking into account the fossil fuel inputs required to make and supply ethanol, Dennis Avery of the Hudson Institute estimates that it would take 546 million acres of U.S. land to replace our current gasoline use with corn ethanol.

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