I'm starting to worry about this as well - not about petrol running out which is highly unlikely but by the prices going up so high you'll need to be very well off to run even a small a car. Hydrogen fuel cells are the answer but what will happen to sports cars? I mean can you imagine production cars with 300KW engines? Such a thing will probably use up more current in one hour of driving on a track than an average house does in a week.
At the moment, thanks to how weak the dollar is, the petrol prices aren't that bad. Over here they've risen only by 8p in the last 2 years. But 2 years ago, the dollar was worth 50% more than it is now. So that's a bit worrying. I've always wanted a very powerful car like an Evo, M5 or RS4 but have been putting off buying one until I'm say 26. However with the projected petrol prices in a few years time being as they are, running a car like that will be harder on the wallet than actually buying one. So I guess it's now or never, if you want to get something which gobbles up petrol, get it now or be prepared to buy a Prius in the future