I didn't know the precise figure, but obviously, like so many other things, the world's oil reserves are finite. It's symptomatic of man's greed. 'We' have been using up the world's resources like there was no tomorrow, with no thought of the consequences for future generations.
I wouldn't worry about the oil though. There are viable alternative energy sources which can and will come into day to day use - just as soon as the energy companies can work out how to corner the market and so preserve their income and profits.