Spear

There is no way the airlines can continue to loft that much metal across the skies at the rate of oil depletion we are witnessing. The only way to keep air travel viable is to lessen the fuel required, and the only way to do that is with airships, or dirigibles. They are slower, but use far less energy to carry a greater load.
There are a few other benefits, including greater safety as they don’t drop from the sky when power is lost. Passenger areas can be more accommodating than a cramped jet, and you won’t get much of a bang out of crashing one into a building, or anything else for that matter