The unfortunate truth is, that this question is not some remote Holywood scenario, but is VERY LIKELY to take place during our lifetime. Many experts believe that the output of oil will reach its climax around 2015 and that from there on it will run out.
Oil consume is soaring with more and more cars around the world (for example China begins to get motorized now) and many fat, heavy cars burning an unnecessary large amount of gas.
There are large amounts of a kind of sand mixed with oil to be found in Canada. I think that stuff is called tarsand or something like that, and the amount of oil that could be gained from it is about twice as much as there ever was to be found on the Arabian peninsula. However, no way has been found so far to separate the sand from the oil.
They are also thinking about developing Hydrogen fuels which would not only be much cheaper, but also wouldn't harm the environment and would never run out, but this so far is utopism.
The thing is that the effects of oil running out would go much further than us having to take a little walk to a grocery store Arvens. Once you walked there you'd find that there are no groceries in the store, because without fuel no trucks could bring the food to the shop! The whole economic system is today based on oil, and the limitation of our private driving is sure the least terrible effect that would be caused from oil being gone.
Are you aware that oil is essential for the production of plastic? Now count the products we use in our daily live that don't contain any plastic. Not too much, isn't it? What if the production of plastic suddenly became impossible due to lack of oil?
Apart from these economic effects, are you aware of the tremendous importance of oil in the world policy? I'm not one of those who say that oil was the one and only reason for the war on Iraq, but I do not doubt that it was one of the main points. There are people who dread the idea of the invention of a fuel that could replace oil, because the huge political power of these people is based on oil.
Why do you think the governments of our countries frequently "court" the rulers of Saudi Arabia, one of the crulest and corruptest regimes in the world?
Because our governments know who dependant we are on their oil, and so long they keep the oil flowing, who cares about young girls being publicly beheaded in Saudi Arabia's capital Riad for being raped by a man who was not her husband? Sorry for this directness, but that's unfortunately the pervert way it is!
I am not one of those people who relish in announcing doomsday. In fact I am convinced that there are ways to cope with the upcoming problem. The question is if humans will be smart and in some cases selfless enough to go these ways.