From The Airport Wiki

Southwest Airlines Co. (NYSE: LUV) is an American low-fare airline based in Dallas, Texas, with its largest focus city at Las Vegas' McCarran International Airport. It is the largest airline in the United States by number of passengers carried domestically per year and the second largest airline in the world by number of passengers carried.[1] It is also the 6th largest U.S. airline by revenue. It also maintains the fourth-largest fleet of aircraft among all of the world's commercial airlines.

Southwest Airlines has carried more customers than any other U.S. airline since August 2006 for combined domestic and international passengers according to the U.S. Department of Transportation’s Bureau of Transportation Statistics.[2] Southwest Airlines is one of the world's most profitable airlines and in January 2007, posted a profit for the 34th consecutive year.