'Peak oil' does not refer to the time when 'oil runs out'. Rather oil production follows a type of bell curve, although as critics have pointed out, sometimes the curve is assymetric and can vary somewhat in different fields. Of course the curve can also be altered by increasing the estimated size of the reserve.
The peak of 'peak oil' is represented by the top of the curve. After a single oil well or oil field reaches the peak, its production begins to decline. At this point you are not 'out of oil' you are out of 'cheap oil.' After peak oil is reached you might still have 20 or 30 years of oil left, but the oil becomes increasingly expensive to remove from the ground, and thus the price rises. Oil still remains in the ground but it becomes increasingly difficult and more expensive to pump up. Finally towards the bottom of the tail of the graph on the down side, it takes more energy to pump the oil out of the ground than can be recovered by using the oil. At this point the oil has become worthless as an energy source, although it might still have value for some other use, and as you slide down the graph towards this point the oil becomes increasingly expensive, and, in addition, the amount of recoverable energy you can gain from the oil keeps going down (because it takes more and more energy to recover the oil, which means that in the end you have less and less net energy gain). This is the phenomena of peak oil (not 'running out of oil'). So if the optimistic estimate is correct, you have 25 years of cheap oil, followed by 25 years of growing crisis, if your economy still depends on oil at that time.
The following is an example of a page which dismisses peak oil as a potential economic problem...