VICTORVILLE, Calif.  For the first time since their industry was deregulated in the late 1970s, airlines in the United States have managed to hold the line on the number of planes they fly.

Evidence of this discipline can be seen at airports around the country, where empty seats are increasingly difficult to find and fares have jumped. It can be seen at a former military base here on the edge of the Mojave Desert, where a record number of airplanes are stored, awaiting better days. And it is reflected in the airlines’ bottom line as the industry returns to profitability.

The airlines tried repeatedly in the past to maintain such capacity restraint, but each time, their efforts fell apart as new competitors sprang up and vied for market share. But this time has been different because of a unique set of circumstances  a result of both the weak economy and the repeated shocks the industry has suffered in the last decade.

The steep jump in oil prices, starting three years ago, forced the airlines to slow orders of new planes. Then, as the recession hit, more than a dozen airlines went out of business, and higher financing costs made it harder to establish new ones. A string of mergers among the big carriers further shrank the number of players. And even low-cost airlines, which once provided the most feisty competition, lately have shown signs of caution.