[CydeWeys]

There are jet fuel futures. If they speculate on crude and then jet fuel itself goes up because e.g. a big jet fuel refinery blew up, they're screwed, because the crude future didn't actually hedge against the specific problem they're facing, and now they have to pay a lot more for jet fuel. Or it could be any other problem that specifically affects jet fuel but not crude in general.

Anyway, as usual, Wikipedia has a relevant article, and it seems that airlines do both: https://en.m.wikipedia.org/wiki/Fuel_hedging