While Southwest Airlines is the world’s largest low-cost carrier, with over $21 billion in annual revenue, United Airlines operates a large domestic and international route network spanning six continents. As of 2018, there were 58 airlines in the US, out of which 17 were classified as major carriers with more than $1 billion in annual revenue. However, nearly 55% of the US airline revenue comes from the top 4 airlines. Customers don't have alternatives that they could use instead, which requires them to make a purchase from one of the companies in the oligopoly. The largest of them is Service...