Ethanol contains about 76,000 B.T.U.s per gallon. Gasoline contains about 114,000 B.T.U.s per gallon. Therefore, to get the same amount of energy contained in a gallon of gasoline, a motorist must buy about 1.5 gallons of ethanol.

Fueleconomy.gov, a site run by the federal government, advises that vehicles running on the most common form of ethanol-blended fuel, E10 (which contains 10 percent ethanol and 90 percent gasoline), will typically get “3 percent to 4 percent fewer miles per gallon” than they would if they were running on pure gasoline. That mileage penalty — in essence, a tax — must be paid at the pump through the purchase of additional fuel.

And that takes us to the cost issue. Since 1982, officials in Nebraska (which is the second-largest ethanol producer, behind Iowa) have been monitoring monthly and annual wholesale, or “rack,” prices for ethanol and gasoline at fuel depots in Omaha. In December 2014, the rack price of a gallon of ethanol was $2.40, while a gallon of unleaded gasoline was $1.73. But recall that we need 1.5 gallons of ethanol to match the energy contained in a gallon of gasoline. That means you would need to pay about $3.60 to get the same amount of energy as from a gallon of gasoline, making ethanol about twice as expensive.

That’s not unusual. Since 1982, the price of an energy-equivalent amount of ethanol has, on average, been about 2.4 times the price of gasoline. Furthermore, for eight full years between 1986 and 1998, ethanol cost at least three times more than an energy-equivalent amount of gasoline. In fact, since 1982, ethanol has always been more expensive than gasoline.

The same energy-equivalent prices allow us to estimate the annual cost of the ethanol tax. Between 2007 and 2014, about 92.5 billion gallons of ethanol were mixed into domestic gasoline supplies. Over that eight-year period, the energy-equivalent cost of ethanol averaged about 90 cents per gallon more than gasoline.