Passenger traffic on U.S. carriers dipped nearly 13 percent in November, the largest monthly decline in nearly seven years and another sign of the erosion in travel demand.

About 8 million fewer people flew on U.S. airlines in November compared with the same month a year earlier, according to the latest data from the U.S. Bureau of Transportation Statistics. It marks the ninth consecutive month that traffic has declined compared with the same period in 2007.

Passengers started scaling back on travel last spring as gas prices skyrocketed and airfares increased. That trend accelerated as the economy soured.

"The November decline is deeper and more alarming than I had been expecting," said Scott Hamilton, an aviation consultant at Leeham Co. in Washington.

"Obviously, the decline, in general, is indicative of the economic conditions, which have really gone south since the financial market meltdown."

Denver International Airport has fared relatively well, though traffic levels have been more volatile than in the past. DIA's traffic dipped 4.7 percent in November - the first monthly decrease in two years - but rebounded in December with a 4.8 percent increase.

The declines in Denver and nationwide during November aren't quite as severe as they seem: The Monday after Thanksgiving - a busier-than-normal travel day - fell in December last year compared with November a year earlier. Still, it's a worrisome development for an industry that was hit hard last summer when fuel prices rocketed to new highs.

Traffic on U.S. carriers through November of last year fell 3.5 percent, with most of that coming in the second half of 2008. Domestic travel was hit the hardest, sinking 13.6 percent in November and 4.2 percent for the year. But traffic on international routes, which offer higher profit margins, also took a hit.