The US aviation market continues to show resilience with steady capacity growth from major legacy carriers, though it is currently witnessing a significant restructuring among low-cost carriers (LCCs). American Airlines remains the dominant force in the market, while Florida has emerged as the primary growth engine for domestic capacity. Despite overall growth, some segments—particularly ultra-low-cost carriers like Spirit—are seeing double-digit capacity reductions.
1. Top 10 Busiest US Airlines
The “Big Three” (American, Delta, and United) and Southwest continue to command the majority of the market share. Notably, American Airlines alone accounts for 21% of all scheduled seats in the US.
| Rank | Airline | Scheduled Seats (Dec 2025) | Market Share |
| 1 | American Airlines | 21.3 million | 21% |
| 2 | Southwest Airlines | 19.3 million | 19% |
| 3 | Delta Air Lines | 18.8 million | 18% |
| 4 | United Airlines | 17.5 million | 17% |
| 5 | Alaska Airlines | 4.3 million | 4% |
| 6 | JetBlue | 3.8 million | 4% |
| 7 | Spirit Airlines | 2.5 million | 2% |
| 8 | Frontier Airlines | 2.3 million | 2% |
| 9 | Allegiant Air | 1.4 million | 1% |
| 10 | Hawaiian Airlines | 0.9 million | <1% |
Key Insight: Spirit Airlines recorded a massive 33% decrease in capacity compared to December 2024, losing roughly 1.24 million seats.
2. Growth Leaders (Year-on-Year)
While the industry average capacity is growing at roughly 3-4% annually, certain carriers are expanding aggressively.
- Largest Volume Increase: American Airlines (+801,800 seats vs. Dec 2024).
- Fastest Growth Rate (Domestic): Breeze Airways increased capacity by 43% year-on-year.
- Fastest Growth Rate (International into US): Cathay Pacific saw a 41% increase in capacity to the US.
3. Busiest US Domestic Flight Routes
The corridor between the East and West coasts remains the most lucrative and high-volume segment of the market.
| Rank | Route | Seats (Dec 2025) | YoY Growth |
| 1 | New York (JFK) – Los Angeles (LAX) | 302,700 | +8% |
| 2 | Atlanta (ATL) – Orlando (MCO) | 285,400 | +2% |
| 3 | Las Vegas (LAS) – Los Angeles (LAX) | 265,100 | -14% |
| 4 | Atlanta (ATL) – New York (LGA) | 250,400 | +15% |
| 5 | Honolulu (HNL) – Kahului (OGG) | 240,200 | -13% |
Key Trend: The Atlanta to New York (LGA) route saw the highest percentage growth (+15%), indicating a strong recovery in business/short-haul travel.
4. Major Infrastructure Hubs
Atlanta Hartsfield-Jackson remains the undisputed king of US airports, though Chicago O’Hare is currently the fastest-growing major hub.
- Busiest Airport: Atlanta (ATL) with 5.2 million seats.
- Biggest Gainer: Chicago O’Hare (ORD) added 351,300 seats compared to last year.
- State with Highest Capacity Increase: Florida (+371,700 seats), driven by leisure demand and the expansion of secondary airports.
5. 2025 Market Outlook
OAG’s analysis points to several defining trends for the remainder of the year:
- Capacity Discipline: Airlines are carefully managing seat growth to protect profitability; global net profit margins are expected to hover around 3.7%.
- High Load Factors: Average load factors are expected to reach 84%, meaning flights will remain crowded.
- Fare Stability: Despite lower oil prices, airfares are unlikely to drop significantly due to high operational costs and a strong US Dollar.
