**Updated for summer 2026**
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Four carriers account for more than three-quarters of the US airline market's 741 million seats this summer.
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Summer 2026 schedule data reveals how firmly the top US airlines hold their grip, which airline is outpacing the rest, and where the cracks are starting to show.
Infographic: The biggest US airlines, summer 2026
How many seats are US airlines flying in summer 2026?
US airlines have scheduled 741 million departing seats across the summer period. The top 10 carriers account for 683 million of those - that's 92% of total US capacity - leaving just 8% split across more than 100 other operators.
That concentration is not new, but the degree of it is still striking. The four biggest US airlines alone -American, Delta, Southwest, and United - hold 562 million seats between them, representing 76% of all US capacity. The gap between the fourth-largest carrier, United, and the fifth, Alaska Airlines, is 85 million seats.
The top 10 US airlines by seats, summer 2026
| Airline | Departing seats | Share of total |
|---|---|---|
| American Airlines | 160.5m | 21.7% |
| Delta Air Lines | 140.4m | 18.9% |
| Southwest Airlines | 133.4m | 18.0% |
| United Airlines | 127.7m | 17.2% |
| Alaska Airlines | 43.1m | 5.8% |
| JetBlue Airways | 25.1m | 3.4% |
| Frontier Airlines | 22.1m | 3.0% |
| Allegiant Air | 13.1m | 1.8% |
| Spirit Airlines | 10.7m | 1.4% |
| Breeze Airways | 6.8m | 0.9% |
American Airlines is the largest US airline by seat capacity, with 160.5 million scheduled seats, 23% more than United in fourth place. Delta and Southwest sit closely together in second and third, separated by fewer than 7 million seats. Below Alaska, the drop-off is steep: JetBlue in sixth has 25.1 million seats, and Breeze in tenth has just 6.8 million, a fraction of what the Big Four each operate.
United Airlines is growing fastest among the top US airlines
Of the four biggest US airlines, United is adding capacity at the fastest rate and is up 9% year-on-year. That growth is not just in seat numbers. United has added 51 net new domestic routes and 8 net new international routes compared to summer 2025.
American Airlines is not standing still either, adding 27 domestic and 13 international routes. Even Delta and Southwest, the more conservative growers, each added routes on both fronts.
| Airline | Domestic routes S25 | Domestic routes S26 | Net change |
|---|---|---|---|
| American Airlines | 880 | 907 | +27 |
| Southwest Airlines | 845 | 859 | +14 |
| Delta Air Lines | 737 | 743 | +6 |
| United Airlines | 667 | 718 | +51 |
| Airline | International routes S25 | International routes S26 | Net change |
|---|---|---|---|
| United Airlines | 326 | 334 | +8 |
| American Airlines | 293 | 306 | +13 |
| Delta Air Lines | 215 | 226 | +11 |
| Southwest Airlines | 71 | 77 | +6 |
Alaska Airlines now includes Hawaiian Airlines
One structural change worth noting: Hawaiian Airlines flights transferred to Alaska Airlines (AS) from 22 April 2026. Alaska's 43.1 million seats in summer 2026 therefore include what was previously reported as Hawaiian's capacity. This consolidation has pushed Alaska firmly into fifth position among the biggest US airlines, a slot Hawaiian held independently just one summer ago.
Spirit Airlines: the sharpest contraction in the market
While the top US airlines are expanding, Spirit Airlines tells a very different story. Spirit has cut its scheduled seat capacity from 23.3 million in summer 2025 to 10.7 million in summer 2026 - a reduction of 54% in a single year as the carrier restructures under Chapter 11 bankruptcy protection.
That decline has not redistributed airline capacity evenly. The major carriers, rather than smaller competitors, appear to have absorbed the routes and demand that Spirit vacated - further reinforcing the dominance of the top US airlines heading into 2026.
What the data tells us
The US airline market in summer 2026 is defined by three things: the structural dominance of four carriers, a capacity expansion led by United, and the compression of smaller operators under financial pressure.
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 >>
