Priceline.com (PCLN) says second quarter 2008 bookings rose 70.9% year-over-year, to $2.1 billion - but there may be turbulence ahead.

The company posted the gains in a souring economy marked by rising fuel costs, airline cutbacks and increasing numbers of people staying home during vacation season.

"Economic uncertainty and high fuel prices are affecting the broad travel market and significant airline capacity reductions in the fall will also have a negative impact," Jeffrey H. Boyd, the firm's president and CEO, said in a prepared statement. "Through the first half of the year, we believe that the positive trends impacting our domestic and international businesses have overshadowed these negative influences."

But he remains optimistic about the future.

"We believe these trends position us for attractive top line and earnings growth for the balance of the year and beyond," Boyd says.

Growth in rental cars and hotel reservations is also slowing, apparently reflecting the economic slowdown. However, Priceline appears to be capturing a solid share of the European and Asian markets.

But investors look to the future and apparently don't like what they see. In early trading Wednesday, Priceline's stock was down $15.78, or about 13.5%, to $101.42. The 52-week range is $59.50 to $144.34.

Priceline's competitors include Expedia (EXPE), Orbitz Worldwide (OWW) and Travelocity, among others.