Cars need energy to move (duh). In a current car, that energy invariably comes from oil. In a fuel cell car, that energy comes from whatever is used to make the hydrogen. Oil is a perfectly fine "original" source for this energy, but unlike current cars, so is the sun, the wind, uranium, the tides, coal/natural gas, alcohol, and hamster wheels.this means that, unless some governments become lower orders of pussies and go nuclear, in all likelyhood oil will be burnt to create the hydrogen to be used in the cars.
I hope that came out at least semi-coherent.