In 2016, the U.S. airline industry generated total operating revenue of over 200 billion U.S. dollars, making the United States one of the largest markets for the airline industry worldwide. The country also has about a third of all airports in the world - more than any other country: around 15,000 airports of all sizes, out of which more than 5,000 have paved runways. Hartsfield-Jackson Atlanta International in Georgia is the busiest airport in the country, having handled a little over 101 million passengers in 2016 alone.
Major airline companies in the United States can be classified into three categories: mainline passenger lines, regional airlines and freight carriers. Mainline passenger companies include carriers such as Alaska Airlines, Delta Air Lines, JetBlue, Hawaiian Airlines, Southwest Airlines, United Airlines, American Airlines or Virgin America. Regional airlines include the following carriers: Envoy Air, ExpressJet and SkyWest Airlines, while the largest freight carriers are FedEx Express and UPS Airlines; these two companies topped a worldwide ranking of airlines based on cargo volume in 20156.
In 2016, the ultra low-cost carrier, Allegiant Air, had an operating margin of 30 percent, followed by Ryanair. Based on revenue passenger kilometers (RPKs), Chicago-headquartered United Airlines came second in a worldwide ranking, with around 28.3 billion RPKs, while Southwest recorded the largest amount of domestic enplanements: just under 149 million in 2016.