It is difficult to say when crude oil will run out because no-one knows exactly how much oil there is left in the world.
There are over 1 trillion (1 million million) barrels of crude oil in proven oil reserves
At current rates, this will last about 44 years, but the amount of oil used in the world increases each year.
Some scientists believe there is a lot more oil still to find, but others think that most oil has already been discovered.