United Airlines and Delta Air Lines are two of the ‘big three’ legacy carriers in the US, with some of the largest fleets in the world. There is no doubt that the US-Europe market is lucrative in commercial aviation, and the airlines offer stiff competition on their transatlantic routes. Both Delta Air Lines and United Airlines have extensive route networks to Europe, but which carrier wins on transatlantic routes?

In this article, we will look in more detail at data from Cirium, an aviation analytics company, based on the airlines’ schedules this month. We will find out more about how many flights these airlines are making to Europe and where they are flying to and from.

We can also see how their fleets differ and if this has any impact on transatlantic flights, as well as how many available seat miles each airline has on its top routes.

United Airlines Takes The Lead

According to data from Cirium in October 2025 for flights from the United States to Europe, United Airlines has some 5,421 services, offering 1,299,793 seats. The busiest route is from Newark Liberty International Airport (EWR) to London’s Heathrow Airport (LHR) and vice versa, with 216 flights each way.

In terms of seats, that’s 36,072 in each direction. When looking at available seat miles (ASMs) as a measure of passenger capacity, this route has 250,051,104 ASMs.

The second most scheduled route is Chicago O’Hare International Airport (ORD) and London Heathrow, with 93 flights each way (186 total). This is less than half the number of flights between Newark and Heathrow, but still a lot of seat capacity, with 31,062 seats available on United Airlines between Chicago and London and back again.

Taking a look at United’s third-busiest transatlantic route, unsurprisingly, it’s to London Heathrow again, but this time from San Francisco International Airport (SFO). This route has 173 flights total in October, fewer than Chicago, but it has a higher number of seats.

Indeed, a total of 47,748 seats are available, offering 256,311,264 ASMs, slightly higher than the Newark route. Available seat miles are worked out by multiplying the number of seats by the number of miles traveled.

Delta Air Lines Comes In A Close Second

Delta Air Lines has scheduled 4,821 transatlantic flights this month, with a total of 1,257,126 seats, putting it slightly behind United Airlines. Its top transatlantic route is from Hartsfield-Jackson Atlanta International Airport (ATL) to London Heathrow with 93 return flights per month (186 in total), the same as United’s Chicago to London route.

These have 23,562 seats available on the outbound leg and 23,635 on the return trip, offering a total of 47,197 seats on this one route.

The second-busiest route for Delta Air Lines is from Detroit Metropolitan Wayne County Airport (DTW) to Amsterdam Airport Schiphol (AMS), close behind at 89 return flights this month for a total of 178 services. This results in 25,647 seats outbound and 25,609 inbound, and respective ASMs of 101,049,180 and 100,899,460.

The following routes both have 87 flights each way, ranking them joint third. These are Amsterdam to Atlanta, with 25,573 seats, and Paris Charles de Gaulle (CDG) to New York John F. Kennedy International Airport (JFK), with 22,027 seats.

The Amsterdam to Atlanta route has 112,546,773 ASMs each way, the highest of Delta’s top transatlantic flights, while Paris to New York has 80,058,145 ASMs.

The United Airlines Fleet

United Airlines has the world’s largest fleet with 1,054 aircraft, per Planespotters.net. The airline operates both Airbus and Boeing aircraft, as does Delta Air Lines, although the long-range fleet at present consists entirely of Boeing aircraft.

United Airlines currently has the Airbus A320 family (A319, A320, A321) and the Boeing 737 on shorter routes.

The long-range and transatlantic routes are currently operated by the Boeing 767-300ER and 767-400ER as well as the Boeing 777-200ER and 777-300ER. The airline also has a fleet of Boeing 787 Dreamliners featuring all three variants: the 787-8, 787-9, and 787-10.

As with Delta Air Lines, the Boeing 767-300ER and 767-400ER will be phased out by 2030, and United Airlines plans to replace them with the Boeing 787 Dreamliner. United Airlines has made a significant investment in the Dreamliner, with orders for over 500 of the aircraft, which will make it the backbone of the widebody fleet.

The airline is also looking to expand its fleet with the Airbus A321XLR to operate on some transatlantic routes, which are expected to be delivered after 2026. The Airbus A350 may also be a future contender in replacing the Boeing 767.

The Delta Air Lines Fleet In Comparison

Delta Air Lines has the third-largest fleet in the world with 989 aircraft, according to Planespotters.net. Its current fleet consists of Airbus A319, A320, and A321 aircraft, as well as the A330 and A350.

Delta also operates a large number of Boeing aircraft, including the 717, 737, 757, and 767. Delta Air Lines operates 4,000 flights daily, to 275 destinations, according to Routes Online.

Delta’s long-range aircraft are mostly twin-aisle aircraft, with the Airbus A330neo and the A350-900 being the newest jets. Although it is establishing a large Airbus fleet, it still uses the Boeing 767-300ER and the 767-400ER on long-range routes such as those mentioned above.

The Airbus A350-1000 will be added to Delta Air Lines’ long-range fleet and will be its largest widebody aircraft. Delta ordered 20 of the aircraft in 2024, and they are expected to be delivered in 2026.

The aircraft will fit in well with its current Airbus A330 and A350-900 fleet, and will replace older aircraft like the Boeing 767-300ER and the Boeing 767-400ER. Delta Air Lines plans to expand its fleet with over 60 Airbus A350s by the end of the decade.

Hubs & Destinations

Delta Air Lines has 11 main hubs for transatlantic flights: Atlanta, Detroit, New York (JFK), Minneapolis-St. Paul, Seattle, Boston, Salt Lake City, Los Angeles, Tampa, Orlando, and Cincinnati. United operates transatlantic flights from seven hubs, including Newark, Chicago, San Francisco, Washington DC, Denver, Los Angeles, and Houston.

Delta also has partner hubs in Europe through its SkyTeam partners in London (Virgin Atlantic), Amsterdam (KLM), and Paris (Air France). In the US, Atlanta is the largest hub. The airline also connects the world through Asia, with hubs in Tokyo and Seoul.

United Airlines uses Newark, Chicago, Washington DC, and San Francisco as gateways in Europe to cities like London, Paris, Rome, and Athens. It also has partner hubs in London and Frankfurt.

This month, United is flying to 25 transatlantic destinations in 12 countries, in comparison to Delta Air Lines’ 25 transatlantic destinations in 15 countries. Although many of the destinations are similar in that they are large European cities such as London, Paris, Rome, and Amsterdam, for example, United Airlines has also chosen a few more unique destinations.

These include the likes of Palma de Mallorca in Spain, Dubrovnik in Croatia, and Porto in Portugal.

The Bottom Line

So, which US carrier wins with the most transatlantic flights? United Airlines, this month, has 5,421 transatlantic flights to Europe, whilst Delta Air Lines has 4,821 transatlantic European flights. United Airlines’ summer schedule for 2025 featured over 760 weekly flights to 40 destinations across its transatlantic network.

Overall, Delta Air Lines operates to 275 destinations on six continents, and United Airlines operates to 300 destinations in 60 countries.

United Airlines has the most international destinations and a higher frequency of flights, as it offers more flights overall and has more available seat capacity. Its most popular long-haul routes serve London, Tokyo, Beijing, and Sydney.

Delta Air Lines is seen as larger by revenue and brand value, and it feeds its hubs for long-haul travel, whereas United Airlines looks for direct routes. Delta also offers a reliable passenger experience and is the most on-time airline, per Business Insider.

United Airlines focuses on transatlantic and transpacific routes and will expand its fleet using the Boeing 787 Dreamliner to replace the aging Boeing 767 fleet.

The airline is focused on its ‘United Next’ strategy, using more fuel-efficient aircraft and sustainable aviation fuel (SAF), as well as improved cabin interiors and better Wi-Fi. It also intends to expand its transatlantic network.

In the future, similarly, Delta Air Lines will focus on using the Airbus A350 for long-range flights and the use of SAF, as well as modernizing cabin interiors. It is not currently known if it plans to operate more transatlantic flights.