25-40 years.
I have been hearing that for more than 30 years. THe fact is that there is more than enough oil to keep us going to 200 years, long after this planet gets to the temperature of venus.
Drilling and exploration technologies continue to improve faster than consumption, hence the low oil prices (except for occational artificial price spikes created by OPEC restricting production)
Eventually a long time from now it will get expensive to drill for oil as it will not be as convientiently located and then prices for oil will rise and demand for it will drop with alternative sources becoming viable. The market will fix all believe it or not.
In the meantime, they are opening up new wells in pennsylvania (my buddy just got a very profitable one on his property) due to the improved drilling and exploration technology in a field that has been assumed to be depleated for over 50 years.
Go to the store and purchase a liter of Evian water, and you will realize that gasoline in cheaper than water.
The british view of the world really hasn't changed since the "for export only" days at the end of world war II. If self denial makes you happy, have at it.
Cheers
Wino