Shares of Continental Airlines Inc. (CAL) plunged nearly 13 percent and other carriers' stock also fell after the Houston-based airline reported disappointing revenue numbers for December to cap another money-losing year.

Continental, the No. 5 U.S. carrier, said revenue as a factor of capacity fell 4 to 5 percent compared to December 2003. The decline was even sharper after excluding traffic on Continental's regional subsidiary.

Continental blamed much of last month's decline in "revenue per available seat mile (search)," or capacity, to the calendar. For example, Thanksgiving fell earlier in 2004 than 2003, pushing some holiday-return travel into November, the airline said.

Passenger traffic actually increased, Continental reported late Monday, but so did its capacity, offsetting the increase in travel demand.

Analysts said the weaker-than-expected Continental report reflected continuing fare sales that are likely to depress airline revenue through January and perhaps longer.

"People are assuming that yields (revenue per seat) for December and the fourth quarter will be weaker than expected," said Ray Neidl, an analyst for Calyon Securities Inc. "The trend in December is not hopeful, and with all the fare sales going on, you can expect that through the first part of the first quarter."

Goldman Sachs analyst Glenn Engel said Continental's report reflected weakness in the industry rather than specific problems at the airline. Merrill Lynch analyst Michael Linenberg said low fares on the East Coast were spreading to the Caribbean, an important market for Continental.

Engel and Linenberg each raised their estimates of Continental's fourth-quarter loss, to an average of about $230 million. The carrier lost $157 million in the first nine months of the year.

Dallas-based Southwest Airlines Co. (LUV) said Tuesday that paying passengers flew 10.3 percent more miles in December, but the low-cost carrier's aggressive expansion resulted in a 12.2 percent increase in capacity — meaning that its planes flew slightly less full. For all of 2004, however, Southwest's planes were 69.5 percent full, up from 66.8 percent full in 2003.

American Airlines(AMR), the largest U.S. carrier, said Tuesday its December traffic grew 6.1 percent, slightly faster than the 4.9 percent increase in available seats.

Neidl, the Calyon analyst, said other factors weighing on airline stocks include an uptick in already high fuel prices and reports that Delta Air Lines Inc., the nation's third-largest carrier, will slash fares. Delta, the nation's No. 3 carrier, has reduced fares in Cincinnati in what some view as a possible precursor to a broader round of cuts.

Northwest Airlines Corp. (NWAC) , the No. 4 carrier, said the effects of the fare cut would hurt industrywide revenue, though the degree of pain would depend on the details, expected as early as Wednesday.

But Eagan-based "Northwest believes the fare changes being described in reports — cuts of up to 60 percent in some cases — "if it becomes general, would immediately adversely and significantly affect industry revenues."

Continental shares dropped $1.76, to close at $12.20 on the New York Stock Exchange; Northwest shares fell $1.31 or 12 percent to $9.64 on the Nasdaq Stock Market; and shares of AMR Corp., the parent of American Airlines, the largest U.S. carrier, fell $1.03 or more than 9 percent to $10.01 on the NYSE.

Shares of Air Tran Holdings lost 74 cents or 6.9 percent to $9.92 on the NYSE; JetBlue Airways Corp. (JBLU) fell $1.32 or 6 percent to $21.65 on Nasdaq; Delta shares slipped 25 cents or 3 percent to $7.31 on the NYSE; and Southwest shares lost 46 cents or 3 percent to $15.61 on the NYSE.

Continental's December numbers came on the heels of a filing last week from AMR, which said American's fourth-quarter revenue per passenger would fall 2 to 3 percent from a year earlier.

American hopes to recover by cutting costs and increasing revenue by a total of $850 million this year, according to a company memo to employees last month. "Cost savings are a continual process," said spokesman Tim Wagner, who declined to discuss the memo.

Fort Worth-based American hopes to raise $200 million with new fees for booking flights by phone or in person instead of on the Internet, and figures to save millions by cutting jobs and conserving fuel. Analysts surveyed by Thomson First Call expect parent AMR to post a $500 million loss for the October-December period.