Current fleet data from ch-aviation shows that United Airlines has the largest mainline fleet in 2025. In this context, ‘mainline’ means the aircraft that the carrier operates directly, rather than contracting the aircraft to alliance partners, codeshares, and regional subsidiaries.

Read on to discover the shape of United’s huge fleet that has more than 1,000 aircraft. This article will also detail the airlines with the second and third-largest fleets, namely American Airlines and Delta Air Lines, as they are close behind United on this front.

United Airlines Has More Than 1,000 Aircraft In Its Mainline Fleet

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The largest airline in the world by mainline fleet size is United Airlines. This carrier has a massive fleet of 1,056 aircraft, with almost 250,000 seats available. Its most prevalent widebody aircraft is the Boeing 777-200ER, with 55 units. However, the carrier has far more narrowbody jets.

There are four variants of Boeing 737 that the airline has over 100 examples of, including the 737-800 and 737-900ER, and the MAX 8 and 9. The table below shows the top five widebody and top five narrowbody United Airlines aircraft by fleet size, along with the totals across the entire fleet.

Behind this world-leading fleet is a vast graveyard of historical and retired aircraft. This includes older variants of 737s that have now been retired, including 101 737-300s, 84 737-500s, and 25 737-200s. These continue to be replaced by 737 MAXs, and the airline has an order of 167 MAX 10s. The airline has also made huge withdrawals when it comes to widebody jets. Most notably, this includes a historic fleet of 44 Boeing 747-400s.

Delta Air Lines’ Fleet Is Dominated By Narrowbody Jets

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The second largest mainline fleet belongs to Delta Air Lines. Similar to United, this fleet is dominated by narrowbody jets that fuel American hunger for domestic aviation. Boeing 737s play less of a role, although the carrier does have 158 737-900ERs. However, it also flies 127 Airbus A321-200s and 84 A321-200neo jets.

It also has a comparatively modest widebody fleet, dominated by jets on the smaller end of the widebody scale, including 39 A330-900s and Boeing 767-300ERs. The table below shows the top five widebody and top five narrowbody American Airlines aircraft by fleet size, along with the totals across the entire fleet.

Larger widebody aircraft have since been retired by Delta Air Lines. This includes its historic fleet of 16 Boeing 747-400s and 18 Boeing 777s across two variants. Looking into the future, there are 267 firm commitments on the Delta Air Lines order sheet.

Like United, the order sheet includes sizable 737 MAX quantities, including 100 Boeing 737 MAX 10s. The carrier is also investing in the next generation of widebody aircraft, with orders for 20 A350-100s and 6 A350-900s. Like all other US airlines, 777X jets are notably absent.

American Airlines Has 1,001 Mainline Aircraft

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The third-largest airline by mainline fleet size is American Airlines, with 1,001 aircraft. All of its widebodies are Boeing jets, with the carrier’s 15 A330-200s and 9 A330-300s lost to history. Its widebodies include 67 Boeing 777s and Boeing 787 Dreamliners.

American Airlines has a far larger fleet of narrowbody jets, comprising Boeing 737s, Airbus A321s, and A319s. This part of the fleet is dominated by 303 737-800s and 218 A321-200s. The table below shows the top five widebody and top five narrowbody American Airlines aircraft by fleet size, along with the totals across the entire fleet.

American Airlines also has a sizable order sheet with 300 commitments that will ensure it retains its spot in the top three. 737 MAX aircraft take up over a third of this order sheet, with 115 of the delayed 737 MAX 10 jets to be delivered. The airline has also placed big orders for 96 A321-200neos and 48 A321XLRs. The order sheet also indicates that the airline will retain its focus on Boeing widebody aircraft, as it has 22 Boeing 787-9s currently on order.

United’s Enormous Order Sheet Will Ensure It Keeps The Top Spot

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Looking at ch-aviation’s ‘To Be Delivered’ column, it is clear that United will only strengthen its position as the world’s largest airline by mainline fleet in the years to come. The carrier has an enormous 666 jets awaiting delivery. This huge order book is likely due to the aging nature of much of the fleet, which averages 16.9 years old.

That indicates that the carrier will look to retire hundreds of aircraft as these new jets begin to be delivered. The table below shows all of the aircraft that United Airlines currently has on order, also using the ch-aviation dataset.

What stands out immediately about this order sheet is the astonishingly large commitment to the 737 MAX 10, an airliner that is still awaiting certification. This May, United estimated it would begin receiving these jets in either 2027 or 2028. United has looked to the Boeing 737 MAX 9to offset any capacity issues caused by these delays.

The Chief Commercial Officer of United Airlines, Andrew Nocella, told Reuters in May 2025 that “in supply chain terms, we want to make sure we get our aircraft, so we’ve committed to the MAX 9. Until we know the MAX 10 is going to be delivered, we don’t want to have an aircraft that doesn’t arrive.” Nocella also indicated that the airline would not be among those to receive the MAX 10 when it finally gets certification.

The 777X Won’t Be Added To The Fleet

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As United seeks to update and further expand its mainline fleet, a notable absentee, as is the case for the order sheets of every other US carrier, is the Boeing 777X. In an interview with Business Insider in August 2024, the carrier’s Senior Vice President of Global Network Planning and Alliances, Patrick Quayle, stated that the new Boeing widebody does not fit United’s business model, so the carrier would not be making an order.

The decision reflects United’s move away from high-capacity jets, which come with a much higher risk and greater operating costs. United has a multi-hub business model, which means its traffic is dispersed. Furthermore, the jets already in United’s fleet are capable of flying non-stop from the West Coast to Europe, making long-haul point-to-point operation possible without needing new planes.

Where Does United Airlines Fly Its Vast Fleet?

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In 2024, data from Cirium, an aviation analytics company, showed that United Airlines had 1.6 million flights scheduled across the calendar year. May alone saw the airline serve 944 routes. All of the ten busiest routes were domestic, usually from Chicago to other American cities. The busiest was from Chicago to LaGuardia with 435 flights a month, averaging 14 a day.

This substantial domestic market explains why United and its close competitors have such incredible quantities of narrowbody aircraft. United Airlines also caters to a substantial international market. In May 2024 alone, the carrier flew to 122 destinations outside of the USA with 283 international routes.

The busiest international destination was Toronto Pearson International Airport. The carrier flew there 697 times in May, with flights originating from Denver International Airport (DEN), Newark Liberty International Airport (EWR), Washington Dulles International Airport (IAD), George Bush Intercontinental Airport (IAH), Chicago O’Hare International Airport (ORD), and San Francisco International Airport (SFO)

United Airlines offers many flights to Europe and Asia. The busiest in May 2024 was to London Heathrow Airport. The carrier flew there 620 times in May 2024 from Denver International Airport (DEN), Newark Liberty International Airport (EWR), Washington Dulles International Airport (IAD), George Bush Intercontinental Airport (IAH), Los Angeles International Airport (LAX), Chicago O’Hare International Airport (ORD), and San Francisco International Airport (SFO).