One way of measuring efficiency is to consider how much energy is contained in the fuel you put in the car and how much of that energy is used to move the car. For a petrol car, about 15% of the energy in the petrol is used to move the car. In a fuel cell car, however, around 60% of the energy in the hydrogen fuel is used to move the car. So fuel cell cars are about four times more efficient than petrol cars.
