THE AMOUNT of fossil energy needed to produce a gallon of ethanol is lower than the fossil energy needed to produce gasoline. But the total amount of energy, including solar, needed to produce a gallon of ethanol is greater than that needed to produce a gallon of gasoline.

A portion of total energy in the ethanol cycle is solar energy that ends up in corn, according to the Greenhouse Gases, Regulated Emissions and Energy use in Transportation (GREET) model developed by Michael Wang, Argonne National Laboratory. Because this energy is free, renewable and environmentally benign, it should not be taken into account when calculating energy balance, states the Department of Energy's Office of Energy Efficiency and Renewable Energy.

The fossil energy input (which is not free) per unit of ethanol is .78 million Btu of fossil energy consumed for each 1 million Btu of ethanol delivered. Meanwhile, it takes 1.23 million Btu of fossil energy to produce 1 million Btu of gasoline delivered. — Lynn Grooms