Southwest Airlines Co. is on pace to unseat American Airlines this year as the world's biggest airline, measured by passenger traffic.
The domestic-only discount carrier already has eclipsed American's combined domestic and international traffic during the first five months of 2007, according to a government tally released Thursday.
Southwest carried 40.3 million passengers on domestic routes between January and May, an increase of 4.2 percent from last year.
"We're thrilled to watch our customer base grow," said Brandy King, a Southwest spokeswoman, who attributed the growth to the company's tradition of friendly customer service. "With so many airlines offering low fares, I think customer service makes all the difference in the world."
American, owned by AMR Corp., carried 40 million passengers during the January-May period, down 1.8 percent from last year's levels. American's international traffic for that five month period was 8.7 million, up 0.3 percent in the first five months; its domestic traffic of 31.3 million was down 2.4 percent.
Last year, Dallas-based Southwest was the No. 2 airline worldwide, according to International Air Transport Association passenger traffic statistics. It carried about 96.3 million passengers, ranking behind Fort Worth, Texas-based American, which carried about 100 million passengers.
American, which could not immediately be reached for comment, has been the top U.S. airline for the past five years, according to the Transportation Department's Bureau of Transportation Statistics.
Rounding out the top five were Delta Air Lines Inc., UAL Corp.'s United Airlines and Northwest Airlines Corp.
Overall passenger traffic on U.S. airlines in the first five months of the year was up 1.8 percent from last year, with 307.9 million total passengers.
In May, U.S. airlines carried 64.7 million passengers, up 0.4 percent from the same month last year.