Airlines go to the commodities market to "book" their oil prices a year or two ahead. Sometimes they win, sometimes they lose.
Because current oil prices are lower in the past doesn't mean the airlines are running all cheap jet fuel. They may be buying jet fuel based on past oil contract prices.
Airline industry profits do appear to be much higher than in years past, however. It appears they're investing those profits in new capital expenditures--new model airplanes that are more efficient on fuel. Hopefully there will be enough competition within this industry to keep airfares reasonably priced.
In the meantime, I'm flying on Norwegian Air Shuttle to Copenhagen for about 1/2 that of other international air carriers. Otherwise, I'd be traveling in North America this year.