In 2012 the total world oil consumption is: about 5 billion tons.

Global oil consumption reaches 88 million b/d (barrels/day)
88 million * 365 days =
32120 million barrels /year =
32120/7 = 4588 million tons =
4.6 billion tons / year.

Total world oil reserve is 1,481,526 million barrels.
=
281,526 million tons
=
281 billion tons

So roughly, we can go with oil for 281/5=50 years, let’s say, in 30 years, we will run out of oil.