US-based low-cost carrier 
Southwest Airlines is unique in several different ways. The carrier is unquestionably the leader in low-cost aviation in the United States, much akin to Ryanair in Europe. The airline is the only carrier operating in the United States with a market share that comes even close to matching airlines like United Airlines, Delta Air Lines, and American Airlines. Competitors like Frontier Airlines, JetBlue, and Spirit Airlines simply come nowhere close to matching the size and scope of Southwest’s operations. Furthermore, the carrier is the only such airline in the United States to have a loyalty program anywhere close in membership to that of the big three airlines.