Measure of the distance a vehicle can travel by consuming only one gallon of fuel. Multiplying this ratio by the total capacity of a vehicle's fuel tank gives the maximum mileage the vehicle can travel in one trip without refueling.
"This new compact car gets over 30 miles per gallon."
An irrelevant reference to oil/gasoline in the American culture. While it is paramount to Americans that they have oil, the amount that they burn is of no concern. In the American culture, "wasting oil" means using it for something other than their luxury purposes and the polution generated by their oil use qualifies them for tax relief.
My Humvee, that I got for free with my tax write-off, gets 3 miles per gallon on the freeway but I don't care!