Southwest Airlines Co. (NYSE: LUV) is an American low-cost airline base 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 (as of December 31, 2007) also the largest airline in the world by number of passengers carried. 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. (Tied 4th place with Northwest Airlines)