When we will run out of oil?

Why is the price of gas so high? I still have not seen anyone come out with a definitive reason of why.
How much oil really is left in the world? Basic Economics say when supply is low and demand is high then prices will increase, well Saudi Arabia does not want to increase the supply saying that there is no need. Is it possible Saudi Arabia does not have as much oil as we may think? I have seen stats that we have a forty year supply of oil in the world. If this is true that is scary so in forty years there is going to be life without oil? Do the experts even know for sure I mean every country seems to not give the real stats on their countries oil supply.