Personally, I recon that Bio-mass fuels will be the answer. To be efficient, aircraft fuel has to have a high calorific value per kilo. Oilseed rape and sunflowers are the two which may offer a solution in the short term. However, until our politicians structure taxation policies that reward long term investment we'll just carry on burning until the oil runs out. But there again, maybe we could burn politicians (and lawyers while were are at it)? They appear to be capable of emitting vast amounts of hot air when heated up.