Great question!! And I think about it whenever I look at a car I might like to own-- I think about spending a lot more to fill it up one day than I need to now...
As long as we don't put any more price ceilings like we had until 1979, at least there will not be shortages. The price will go up commensurate with Supply and Demand.
As that happens, other sources of energy will become financially more feasible-- biodiesel for starters, electric cars, with electricity coming from solar, windmills, and probably some nuclear as well...
The fact is, we've always come up with new sources of energy when the old sources ran out (ie, firewood, coal when coal mines in the UK ran out, etc). One of my history teachers brought that up and for some reason I remember it...
What I plan to do is put systems in my house that will use solar power to cut down on the amount of electricity I have to pay for, and one day have perhaps an electric car, or maybe even a biodiesel plug-in hybrid?
We'll work it out!