Other than Southwest, US airlines haven't engaged in fuel hedging for at least a decade. As with basically any kind of insurance, they've basically found it loses money overall assuming that the price spikes aren't catastrophic (arguably WN lighting money on fire for fuel hedges for a decade damaged their finances enough that it made them easy pickings for Elliott). Even the airlines that hedge (e.g. the European airlines) generally only hedge at most a low-double-digit percentage of their needs.

DL does effectively hedge out fluctuations in crack spreads by owning an oil refinery (near PHL, IIRC). UA also indirectly hedges out oil by having an IAH hub.