Diesel fuel is less-refined oil product that petrol and is used in an engine
that uses higher compression than a petrol engine to ignite the fuel, instead
of a spark plug.
Diesel cars tend to use much less fuel than petrol cars.
This is especially the case with large 4x4 wagons and off-roaders that can use
half as much fuel as their petrol equivalents. Diesel engines producing good
performance tend to be turbocharged.