A good question

With oil near $130 a barrel, why does Southwest Airlines stand alone in the airline industry in its aggressive use of hedging to keep fuel costs under control?

Southwest has locked in more than 70% of its jet-fuel requirements this year at a price equivalent to $51 a barrel for crude oil. By contrast, other big carriers have hedged 30% or less of their fuel needs this year. Those carriers generally expect to pay the equivalent of $85 to $100 per barrel of oil under their hedging programs.

Why Rivals Don't Copy Southwest's Hedging (Wall Street Journal, 28 May 2008)

There are some good attempts at an answer in the linked article.