There isn't enough oxygen left to combine with the remaining carbon atoms. Like gasoline, ethanol is made of carbon and hydrogen, but in addition it contains its own supply of oxygen. In some parts of the U.S., ethanol is mixed with gasoline at 1 part ethanol to 9 parts gasoline to help reduce air pollution. No adjustment is needed for a car's engine to burn this mixture. Some new cars are designed to burn fuel blends of up to 80 percent ethanol.
Ethanol costs more to make than gasoline.
New production technologies may bring the price of ethanol down in the coming years. Another disadvantage is that a gallon of ethanol doesn't hold as much chemical energy as a gallon of gasoline. So even though ethanol burns more cleanly than gasoline, a car won't go as many miles per gallon. Connections Half the oil we use in the U.S. comes from foreign countries. The plants we use to make ethanol are all grown inside this country.