Wikipedia: effect of the 2000s energy crisis:
Although Peak oil theorists such as David Goodstein, Richard Heinberg, and others, had for years predicted sharp declines in air travel following the peaking of world oil production and its subsequent decline,[35] air travel enjoyed robust growth around much of the world spurred by low jet fuel costs starting in the mid-1980s. For example, air travel in the United States grew five times faster than population in the decades after 1978, with 769 million passengers boarding U.S. airline flights in 2007.[36] However, the run-up in oil prices after 2003 began eroding airline profits, and the further doubling of oil prices from May 2007 to May 2008 began to have a substantial impact on airline operations, forcing airlines to reduce flight schedules, and pushing weaker carriers into merger or bankruptcy. During the first half of 2008, at least twenty-five airlines world-wide entered bankruptcy or were forced to cease operations.
April 2008 began with four small airlines (Aloha Airlines, Champion Air, ATA Airlines and Skybus Airlines) ceasing operations in a period of a week. A fifth airline, Oasis Hong Kong Airlines ceased operations on April 9, 2008.[40] A sixth airline, Frontier Airlines filed for bankruptcy on April 11, 2008 to protect itself from its credit card processing company which was withholding airline ticket revenues. Frontier continues to operate under Chapter 11 and is working to get a new agreement with said company. Eos Airlines, a small specialty carrier with high costs, ceased operations on April 27, 2008. An eighth airline Nationwide Airlines ceased operations on April 29, 2008, due to the "impossibility" of profitably operating the Boeing 737-200 with oil prices of over $133 a barrel. The 737-200 is a 30 year old aircraft that is 30% less fuel efficient than new production 737's. On May 9, 2008, a ninth airline, EuroManx announced that it was ceasing all operations, citing rising fuel prices and reduced passenger numbers as the reasons.[41]
A 5% U.S. domestic capacity cut (since raised to around 15%) may be expanded to all airlines to save on fuel by eliminating older aircraft from their fleets similar to the exchange that took place in the late 1970s and early 1980s. Although a slightly larger cut happened in the aftermath of 9/11 (20%), this is the first time since the 1970s that airline service has been cut to save on fuel for the United States. Other airlines such as Ryanair and Scandinavian Airlines System have also cut capacity.[citation needed]
Increasing fuel prices also caused "deep downturns" in air travel within China and India, in favor of a return to ground travel.