**Updated July 2025**
Which are the biggest airlines in the US this summer season? Using our Schedules Analyser, we've brought together data to establish the top 10 biggest airlines based on the number of departing seats in the schedules.
Infographic: The Biggest US Airlines, Summer 2025
Top Ten Biggest US Airlines Operating 727 Million Seats
US airlines have 727 million seats scheduled to depart the US in the summer of 2025, with the top 10 busiest US airlines operating 664 million of these, that's 91%.
74% of US Airline Capacity Provided By The Big Four
The "big four" US airlines - American Airlines, Southwest Airlines, Delta Airlines and United Airlines - have by far the most capacity, accounting for 74% of US airline seats, a total of 538 million between them.
The biggest US airline based on seats, American Airlines, accounts for 21% of capacity in the top ten, followed by Delta Air Lines, with 19%, then Southwest with 133 million seats, 18% of the top ten's capacity. The fourth biggest airline in the US, United Airlines has 117 million seats in the schedule (16%).
The gap between the fourth busiest US airline and the fifth, Alaska Airlines, is 83m seats.
The low cost airlines Spirit Airlines, Frontier Airlines and JetBlue Airways all hold 3% market share with each airline having between 23 and 24 million seats on sale for Summer 2025.
Our US Aviation Market Dashboard is updated each month. As well as the biggest US airlines, we track the busiest airports and look at which states are adding capacity. View the dashboard now. >>
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