FORT WORTH, Texas — U.S. airlines today begin a series of earning reports that will put behind them their longest and deepest losing streak ever: a collective $35 billion loss over the five years ended in 2005.

Dallas-based Southwest Airlines and Fort Worth-based American Airlines are expected to announce full-year profits for 2006, though grounded flights in December from bad weather may have pushed American and other carriers into small fourth-quarter losses.

When reports are in from all the big U.S. airlines in a few weeks, Wall Street is looking for a collective 2006 profit of $2 billion to $3 billion, not counting bankruptcy charges and other one-time accounting items.

Meanwhile, 2007 is starting off with a bang for the airlines, thanks to sharply lower fuel prices, continued strong demand from travelers and industry restraint in adding seats.

The Air Transport Association, the industry's chief trade group, is projecting 2007 profits of $4 billion to $5 billion, excluding one-time items. And that's among the more conservative projections.

As 2006 came to a close, Calyon Securities analyst Ray Neidl told clients that U.S. carriers could earn $6 billion before one-time accounting events this year. And that upbeat outlook was issued before the price of crude oil began its steep drop. Crude oil closed yesterday at $51.21 a barrel, a 19-month low.

Neidl's forecast also came before the latest round of fare increases took hold during what normally is a slack travel period.

Last weekend, most of the United States' big network airlines tacked on $5 each way to the price of their fares. It was the first big fare increase of this year, but at least the 11th industrywide boost since the beginning of 2006, according to JPMorgan analyst Jamie Baker.

What's more, current analyst projections do not factor in what might happen to industry profits should any of the proposed or rumored airline mergers actually happen. US Airways has a pending offer for Delta Air Lines. Orlando-based discounter AirTran is bidding for Milwaukee-based Midwest Airlines.

A wave of airline mergers could be expected to reduce the available supply of airline seats, allowing airlines to further boost fares.

Analyst Susan Donofrio at Cathay Financial is looking for industrywide capacity growth of 4.3 percent, a relatively modest rise. The big network carriers will be most conservative in adding seats, she says, growing by just 2.7 percent, while low-cost airlines will grow about 10.3 percent and regional airlines by 5.4 percent.