United Airlines is one of the big four US airlines and vies with Delta Air Lines and American Airlines (and, in some respects, Southwest) for the title of the world's largest airline. While United has a plurality of the market share in multiple US airports, it only has an absolute majority in one major airport, Newark Liberty International Airport, serving the New York City area. Here is what to know about United's top hubs and their passenger numbers.
United Airlines, one of the world's largest carriers
United Airlines claims to be the world's largest airline saying "United is the largest airline in the world." However, there are various ways to measure the size of an airline. The metric United uses to claim the title is revenue passenger miles.
United, Delta, and American all have mainline fleets of around 1,000 aircraft. As of the time of writing (March 30), Delta Air Lines has the largest market capitalization in the world. Delta has a market capitalization of around $28 billion, while Ryanair, IndiGo, and United are around $23 billion each.
Southwest follows with a value of around $20 billion, while American Airlines is far behind as the 20th most valuable airline at only around $7 billion.
United Airlines flies around 140 million people annually to over 300 destinations across six continents. Separately, Qantas is the one airline that flights to all seven continents as it operates sightseeing flights in Dreamliners over Antarctica.
United Airlines' largest hubs
According to the Bureau of Transportation Statistics (BTS), United Airlines has an absolute majority in one major US airport, Newark Liberty in New Jersey, serving the greater New York City area. There it has a 58.36% share of the airport's passengers.
BTS also reports United as having a large share of San Francisco's passenger traffic (44.41%), Houston's passenger traffic (39.08%), and Denver's passenger traffic (38.16%). At Chicago-O'Hare, it also has a 30% share.
In terms of number of passengers flown through these hubs, Denver leads with 14.4 million passengers, followed by Chicago-O'Hare at 12.5 million, Newark at 6.9 million, Houston at 9.4 million, and San Francisco at 7.8 million.
Data provided by Cirium, an aviation analytics company, shows the most recent flight numbers for United from these major hubs. In March 2025, it is scheduled to operate the most flights from Chicago-O'Hare, with 32,562 flights scheduled carrying a total of 3,976,552 seats.
However, the United aircraft operating from Denver appear to be on average larger than those at O'Hare. There United will operate slightly fewer flights in March (31,169 flights), but they will carry slightly more seats (4,033,296 seats).
Next, Houston Intercontinental will have the third-most United Airlines flights and seats, with 28,912 flights and 3,595,195 seats. United's major hub at Newark will have 22,909 flights and 3,382,195 seats, while San Francisco has 16,243 flights and 2,611,154 seats.
From Newark Liberty, United Airlines and JetBlue are the only US airlines offering international flights. Spirit, American, Delta, and Alaska also have significant operations at the airport, but they only fly domestically from Newark.
There are numerous foreign carriers also operating at Newark, including Turkish Airlines, Air Canada, SAS, British Airlines, and many others. However, the primary NYC international airport is New York-JFK.
Slots at Newark Liberty International Airport
While the major carriers tend to dominate their key-hub airports, this is not always seen as desirable. Slots have long been a sensitive issue at Newark Liberty. Since at least 2016, the FAA has been trying to promote competition at Newark. Slots are the permission to take-off or land at congested airports. United had advocated for these slots to be retired.
In 2016, the Department of Justice reported that it abandoned its attempt to increase its monopoly at the airport by taking over 24 ex-Delta slots. At the time, it would have increased United's slot share from 73% to 75%.
In 2021, the Federal government moved to award 16 slots for flights to Newark to low-cost carriers in an effort to boost competition and reduce United's dominance.
These slots had been previously owned by United, but were then transferred to Southwest and were subsequently given up. Southwest acquired them in 2010 as a condition of the government's approval to the merger with Continental Airlines. Southwest decided to pull out of Newark and instead focus on New York's domestic LaGuardia Airport.
The acting head of the Justice Department's Antitrust Division noted that low-cost carriers help to play an important role in keeping the airline industry competitive and the power of major airlines in check. In this case, the mainline carrier in mind is United.
At the time, Spirit Airlines was seeking to take over 16 of Southwest's most desirable old slots. In July 2022, Simple Flying reported that Spirit won these 16 former Southwest slots.
In late 2024, the FAA announced it would relax slot requirements at Newark due to major construction projects at the airport. Between 2024 and 2026, the airport will undergo multiple states of airside construction projects and these will impart the airport's capacity in various ways.
During the construction, Runway 4L-22R is to be closed on weekends. Meanwhile, Runways 4R-22L and 11-29 are expected to remain open.
Newark Liberty is designated a Level 2 airport for slot purposes by the FAA. The country's other Level 2 airports include Chicago O'Hare, Los Angeles, and San Francisco Airport.
Rival hubs
Whereas United has its main hubs in Chicago-O'Hare, Denver, Houston, Newark, and San Francisco, its rivals have other hubs around the country. The following statistics are per the BTS's 2024 numbers for each major airline.
American Airlines' hubs
American Airlines' major hubs are Dallas/Fort Worth, Charlotte, Miami, and Phoenix. Its largest share of passengers is at Charlotte where it carried 68% of the airport's passengers in 2024 (a total of 17.8 million passengers).
American Airlines has a majority share of the market at three major airports - at Dallas/Fort Worth it has a 67% share, at Charlotte, it has 68% share, and at Miami, it's 59%. Its share at Phoenix is also notable at 32%. By number of passengers, it carried 22 million at Dallas/Fort Worth, 18 million at Charlotte, and 9 million at Miami in 2024.
Delta Air Lines hubs
Delta has a majority share at four major US airports, including the world's busiest airport. At Atlanta, it has a 73% share and carried 33 million passengers in 2024.
Next, it has a 58% market share at Minneapolis, largely thanks to its merger with Northwest Airlines in 2010. The other two major airports where it has a majority are Salt Lake City (57% share) and Detroit (55% share). Delta Air Lines also has the largest share at New York-JFK (28% share). There, it is closely followed by JetBlue and American.
Southwest hubs
Southwest Airlines operates a different model than the other three major airlines. Southwest doesn't operate international flights apart from some sun destinations in the Caribbean, Mexico, and Central America. It doesn't operate flights to Canada as its system can't receive Canadian dollars.
Southwest is considered a hybrid carrier, mixing the low-cost and mainline carrier models. Notably, Southwest exclusively operates a fleet of Boeing 737 narrowbody aircraft.
Its largest hub by number of passengers is Denver, where it has a 33% share and carried 12 million passengers. Denver is followed by Las Vegas, where it carried 11 million passengers, while commanding 40% of the airport's market share.
Southwest has an impressive 97% market share at Dallas, where it carried 8 million passengers in 2024. It also has a 71% market share at Baltimore, where it flew 9 million passengers. At Chicago-O'Hare it had a 24% share and carried 9 million.
