Southwest Airlines is the largest airline in the world based on numbers of passengers. It is also the sixth largest US airline based on revenue. The company was founded in 1971 by Herb Kelleher in Dallas, Texas. It now operates more than 5,000 Boeing 737 aircraft between 64 cities with more than 3,300 flights a day. The company boasts that the 2006 year-end results marked their 34 consecutive year of profitability.