Fuel prices are reported in the units in which they are typically sold, for example, dollars per gallon. However, since the energy content per gallon of each fuel is different, the price paid per unit of energy is often different from the price paid per gallon. The following chart shows the average price per gallon, the average price in gasoline gallon equivalents, and the average price in dollars per million BTU as of 2009.

*(per gas gallon equivalent)

Interest in alternative fuels increases when the actual price differential per gallon increases even if the savings is not as great on an energy-equivalent basis.