U.S. airlines are ending a prolonged period of cutting back their flying capacity on domestic routes.

For travelers, the growth in the supply of airline seats could lead to relief from rising air fares. Fliers could also find more elbow room on crowded flights.

"It could spell a little bit of relief," says consultant David Beckerman of Back Aviation Solutions.

According to a USA Today analysis, airlines, including regional partners, will increase their domestic seat offerings by nearly 2 percent in November 2006, vs. November 2005.

Annual growth for December will be about 3 percent from a year earlier. The gains mark the first time since the summer of 2005 that U.S. airlines have increased domestic capacity on a year-over-year basis.

The calculation varies with the airline, but decisions to add seats generally reflect greater optimism in the industry about its prospects for making money.

"When you see the kinds of demand we're experiencing, the only conclusion you can reach is that the market wants more of our service," says David Messing, a Continental Airlines spokesman.

Continental is the only network carrier that has increased domestic capacity every month this year compared with last year, the analysis shows.

Discounters are mainly behind the growth. Combined, Southwest, JetBlue and AirTran added most of the net new seats for December.

John Heimlich, economist at the Air Transport Association, says that strong demand and 14 consecutive months of year-over-year revenue gains for airlines will make some carriers "bullish" about capacity.

But not every airline is as optimistic. No. 1 American, for example, has scheduled slightly fewer seats for November and December, vs. a year earlier.