The United States consumes about 150 billion gallons of gasoline per year and produces about 5 billion gallons of ethanol.

It takes 1.5 gallons of ethanol to provide the energy in 1 gallon of gasoline. One ton of corn yields about 100 gallons of ethanol.

About 12 percent of U.S.-produced corn is used to make ethanol. Here is an open question: Is the energy used in growing the corn and making the ethanol more or less than the energy in the ethanol itself? It depends on the energy required for the operation of irrigation pumps, the possible use of byproducts, etc. In any event, it is a close call. Same can be said for the generation of greenhouse gases.

Richard Hill is a retired professor emeritus of engineering at the University of Maine.