Fuel economy is the amount of gas (fuel) required to move a vehicle over a given distance. Fuel efficiency is the efficiency of converting energy contained in a carrier fuel to kinetic energy or work. Fuel efficiency can also mean the output one gets for a unit amount of fuel input such as "miles per gallon" or "liters per 100 kilometers" for an automobile (sometimes called fuel economy).  

Automobile fuel efficiency can be calculated in either miles per gallon or l/100 km. 

Here are some examples of fuel consumption in MPG:

Toyota Corolla
Model Year: 2007 (Manual (5 speed), 4 cyl, 1.8 L, Regular Gasoline)
City: 28          Highway: 37

Honda Civic (Manual (5 speed), 4 cyl, 1.8 L, Regular Gasoline)
Model Year: 2007
City: 26          Highway: 34

Chevrolet Aveo
Model Year: 2007 ( Manual (5 speed), 4 cyl, 1.6 L, Regular Gasoline, EMS )
City: 23          Highway: 33

Sentra Nissan
Model Year: 2007 ( Manual (6 speed), 4 cyl, 2 L, Regular Gasoline )
City: 24          Highway: 31

Volkswagen Jetta
Model Year: 2007 ( Manual (5 speed), 5 cyl, 2.5 L, Regular Gasoline )
City: 19          Highway: 28