United Airlines has solidified its position as the largest airline in the world by mainline fleet size in 2025, operating a remarkable total of 1,056 aircraft. This figure highlights a significant capacity for air travel, with nearly 250,000 seats available across its fleet. The term “mainline” refers to the aircraft that United operates directly, as opposed to those managed through partnerships or regional subsidiaries.
Fleet Composition and Overview
United’s mainline fleet includes a diverse range of aircraft, with a notable emphasis on narrowbody jets. The most prevalent widebody model is the Boeing 777-200ER, of which there are 55 units. In contrast, United operates over 100 examples of four different variants of the Boeing 737, including the 737-800 and 737-900ER, as well as the new MAX 8 and MAX 9 models.
An overview of United Airlines’ fleet is as follows:
| Variant | In Fleet | Average Age (Years) | Total Capacity |
|---|---|---|---|
| Boeing 777-200ER | 55 | 25.7 | 15,524 |
| Boeing 787-9 | 47 | 6.6 | 11,822 |
| Boeing 767-300ER | 37 | 29.7 | 6,680 |
| Boeing 787-10 | 21 | 5.4 | 6,678 |
| Boeing 777-300ER | 22 | 7.9 | 7,700 |
| Boeing 737-800 | 141 | 21.7 | 23,406 |
| Boeing 737-900ER | 136 | 12.9 | 24,344 |
| Boeing 737 MAX 8 | 123 | 2.8 | 20,418 |
| Boeing 737 MAX 9 | 113 | 3.1 | 20,277 |
| Airbus A319-100 | 81 | 24 | 10,206 |
The total fleet averages 16.9 years in age, which has prompted United to look toward modernization. With a significant order book of 666 jets awaiting delivery, the airline is set to enhance its fleet in the coming years.
Competitors in the Mainline Fleet Race
Following closely behind United are American Airlines and Delta Air Lines, which operate the second and third largest mainline fleets, respectively.
American Airlines maintains a fleet of 1,001 aircraft, predominantly composed of Boeing widebodies, including 67 Boeing 777s and a variety of Boeing 787 Dreamliners. Its narrowbody segment features a substantial number of 303 Boeing 737-800s and 218 Airbus A321-200s.
Delta Air Lines ranks second with a fleet of 1,010 aircraft. Similar to United, Delta’s fleet is heavily reliant on narrowbody jets, with 158 Boeing 737-900ERs and a significant presence of Airbus A321s. Delta has also been modernizing its fleet, with a notable order of 267 aircraft on the books, including 100 Boeing 737 MAX 10s.
Both American and Delta have made strategic retirements from their fleets, phasing out older models to make way for more efficient aircraft.
Future of United Airlines’ Fleet
United Airlines’ extensive order sheet reflects its commitment to maintaining its leading position. The largest commitment is to the Boeing 737 MAX 10, with 167 units ordered, despite delays in certification. The carrier anticipates receiving these jets between 2027 and 2028. Additionally, United has placed substantial orders for 153 A321neos and 141 Boeing 787-9s.
Andrew Nocella, Chief Commercial Officer of United Airlines, emphasized the importance of ensuring timely aircraft delivery to address potential supply chain issues. He mentioned in May 2025, “In supply chain terms, we want to make sure we get our aircraft, so we’ve committed to the MAX 9.”
United has opted not to include the new Boeing 777X in its future orders, a decision attributed to its business model which favors flexibility and cost efficiency over high-capacity jets.
Operational Reach and Market Presence
In 2024, United Airlines has a staggering 1.6 million flights planned, serving 944 routes in May alone. The busiest route is from Chicago to LaGuardia, with 435 flights a month, showcasing the carrier’s strong domestic market.
Internationally, United operates to 122 destinations outside of the United States, with Toronto Pearson International Airport emerging as the most frequented international destination. In May 2024, United flew to Toronto 697 times from various U.S. cities.
The airline’s international operations also include significant traffic to Europe, with London Heathrow being the most popular route, comprising 620 flights in May 2024.
As United Airlines continues to expand its fleet and operational capacity, its leadership in the aviation industry appears secure, driven by strategic investments and a commitment to modernization.
