I'ld like to refer to some comments I made in another topic (What should Airbus do?).
Working for a car company and being involved in amongst others these discussions I can asure you that if the "oil" problem was so easily solved as suggested by some of the above, the world would be completely different.
And I am not alluding only to technology but also world economy, politics, basically the whole of the society.
Fact 1: The question is not only when we run out of oil. In fact that question may be totally irrelevant. More important today and in the foreseeable future is what the demand will do. Again as already pointed out, the demand has grown sharply within China and it will continue to do so. Also, the political situation not only in Arabian countries but in all major oil producing countries (Russia is a very recent example, Venezuela is another one). Also trying to estimate what will happen if the world shifts from a oil driven economy to another source (hydrogen, solar power, ...) is very difficult. The complete economical structure of the whole world will change, countries will disappear or change remarkably, ... In any case, such a shift will have to happen very very gradually and will still have enormous chocks and sudden changes.
Fact 2: Although hybrid cars are around (I work for a company that was the first to launch such a car) the technology is not usable for airplanes. Basically the electrical engine is used for starting and once at a certain speed the fuel engine kicks in. Add to that the stop-and-go systems (fuel engine stops running when you stop at for example a red light and electrical engine is used to start off again) and you have the hybrid cars of today and the future. The batteries for the engine are still heavy and are recharged by braking energy. The electrical engine is contributing 0% during cruise.
Fact 3: Hydrogen powered cars will take at least another 20 years. Yes, I know, there are some prototypes driving aroound even as we speak. However, the difference between a prototype technology demonstrator and a mass production car is very big. Many big problems still need to be solved. I will mention only one: reliability. That's still a long way off and be honest reliability is much more severe in aviation. Secondly, the energy necessary to produce hydrogen is enormous and thirdly where to fill up your tank with hydrogen??? Supply of hydrogen may turn out to be the biggest problem overall.
Fact 4: Some form of bioenergy. Probably will become a niche product, especially if the fuel price continues to rise, bioenergy (oil produced from seeds) could become competitive. But production (crops) are much too few to have an impact today. And as stated above, we are talking about diesel here which is nto eactly the kind of fuel airplanes need.
Fact 5: Fuel cells, only this year engineers have cracked the problems with fuel cell cars driving in temperaturs below zero (degrees Celcius) (before that, the cars only worked in positive temperatures). Slowly problems are being resolved but the hydrogen (see fact 3) is still the major problem. And the weight of the fuel cells of course.
Basically what I wanted to get across is that:
a/ the energy problem is difficult enough for car companies to crack let alone for airplanes
b/ car companies are today pursuing different directions which means one thing: no-one is sure and has the correct answer, everyone is trying to come up with a solution but THE solution has not been found yet (and may never be)
c/ it is all much more complex than what some members are suggesting. My small message only gives a very small insight of the problems and issues at stake
d/ don't ask me for a solution because there is no answer to that question yet. The only thing I could see happening is that fuel prices rise sharply (very likely to happen and today's oil prices will seem cheap in comparison) and priorities will be set: cars to use as much as possible hybrid or alternative fuel technologies. Houyseholds and industry to use alternative fuels (gas, electricity, solar power, ...) and aviation being one of the industries to use kerosene as long as possible. What very high fuel prices will do for the traffic levels is a completely different discussion.