Leftfield
While there would be a need to find an alternative fuel such as ethanol or filtered chip-fat, there may also be a change in the mode of transportation from jet ac to something like (cue uncontrollable laughter) .... airships! They have quite a good range and low fuel consumption as well as being able to carry outsize loads. Apart from that, they're rubbish.
But I digress. I would put my money on hydrogen-based fuel for a hydrocarbon replacement. Instability issues of hydrogen fuels would need to be addressed. Also, it is likely that the large amounts of hydrogen fuel required would need to be extracted from seawater, a process which needs enormous amounts energy, and so you're back to square one. I'm sure some bright spark will work it out.