Which US Carrier Operates The Most Aircraft Types In Its Mainline Fleet In 2026?

The three largest airlines in the world are the three US legacy carriers: American Airlines, Delta Air Lines, and United Airlines. Each is roughly comparable in size and has hubs all across the US, but this doesn't mean that their fleets are even all that similar. All three airlines operate the Airbus A320 family and the Boeing 737, but there are some distinct differences in the overall makeup of their narrowbody fleets. Meanwhile, you see even more variety with the three airlines' long-haul fleets.

As of October 2026, United Airlines has the largest mainline fleet of the three, with an astonishing 1,147 aircraft in its fleet. American Airlines is number two, with 1,037 aircraft within its mainline fleet, followed by Delta Air Lines with 1,006 mainline aircraft. These fleets are distinct from the aircraft operated by these airlines' regional partners. Even the smallest of the three, Delta, still operates a much larger mainline fleet than the world's fourth-largest airline, and all three carriers are actively growing.

The Mainline Fleet Makeup Of The Legacy Carriers

American Airlines currently operates the most streamlined fleet out of the three US legacy carriers, as it currently only has the Airbus A320, the Boeing 737, 777, and 787 in its fleet. For such a massive fleet, operating only four types is quite noteworthy. Delta Air Lines, on the other hand, has the most diverse fleet with eight types, using the Airbus A220, A320, A330, A350, Boeing 717, 737, 757, and 767. United Airlines falls in the middle with six types, using the Airbus A320, Boeing 737, 757, 767, 777, and 787.

When you break down the fleets by variants, American is flying the A319-100, A320-200, A321-200, A321neo, A321XLR, 737-800, 737 MAX 8, 777-200ER, 777-300ER, 787-8, and 787-9. This amounts to 11 variants within the fleet.

Delta uses the A220-100, A220-300, A319-100, A320-200, A321-200, A321neo, A330-200, A330-300, A330-900, A350-900, 717-200, 737-800, 737-900ER, 757-200, 757-300, 767-300ER, and 767-400ER, totaling 17 variants. Meanwhile, United uses the A319-100, A320-200, A321neo, A321XLR, 737-700, 737-800, 737-900, 737-900ER, 737 MAX 8, 737 MAX 9, 757-200, 757-300, 767-300ER, 767-400ER, 777-200, 777-200ER, 777-300ER, 787-8, 787-9, and 787-10, amounting to 20 variants.

Once again, American has the most streamlined fleet, but the more interesting distinction is that United operates more aircraft variants than Delta. This is mainly because United operates six 737 variants, three 777 variants, and three 787 variants, whereas Delta only operates two 737 variants and does not fly either the 777 or 787. The latter also does not operate the 737 MAX, unlike its two peers. However, Delta's approach is costlier since it operates more aircraft types.

The Recent Evolution Of The Fleets

The fleets of the legacy carriers are, in large part, a product of their mergers. When Delta merged with Northwest Airlines, it was already flying the 737, 757, 767, and the 777, along with the McDonnell Douglas MD-80 and MD-90, while it inherited the A320, A330, 747, and DC-9. United, which was already flying the A320, 747, 757, 767, and 777, added the 737 to its fleet when it merged with Continental Airlines. American added the A330 and Embraer E190 to its fleet after merging with US Airways, while already flying the A320, 737, 757, 767, 777, and MD-80.

Throughout the 2010s, Delta and United got rid of their 747s, while Delta also retired its inherited DC-9s soon after the merger. United began adding the 787 to its fleet in 2012, while American's first 787 arrived in 2015, and Delta added the Boeing 717 to its fleet starting in 2013 while its first A350s came in 2017. In addition, Delta received its first A220s in 2018 and its first A330-900s in 2019. In the late 2010s, American and United began flying the 737 MAX, while American also added the A321neo in 2019. This was the same year that it retired the MD-80.

During COVID, American retired the A330s, 757s, 767s, and E190s, while Delta retired the 777, MD-80, and MD-90. United Airlines didn't retire any aircraft types during COVID. American and Delta streamlined their fleets significantly, and the only aircraft variant that American has added post-COVID was the A321XLR, while Delta has only added the A321neo. United, however, has added the A321neo, A321XLR, and 737 MAX 8 to its fleet post-COVID (it previously only flew the MAX 9), while it's still operating all of the variants that it owned pre-COVID.

The Benefits And Drawbacks Of The Approaches

American Airlines, with its streamlined fleet of four types and 11 variants, has comparatively low maintenance and crew costs. Staff only need to be trained on four types of planes, and the airline has to maintain fewer parts pools. In addition, the carrier enjoys a high degree of flexibility, given the huge fleets of 737s and A321neos that it operates in particular. For the most part, each type has its own purpose, and there aren't two large fleets serving the same mission.

Delta and United have more variety in their fleets, which allows them to optimize aircraft deployments more effectively. As an example, both airlines operate the 737-900ER, whereas American Airlines does not. This means that it needs to choose between a smaller 737-800 and a larger A321-200 throughout the network, whereas Delta and United have another option. Of course, operating multiple types is more expensive, although there is significantly less cost associated with operating multiple aircraft variants.

Delta has become particularly noteworthy for introducing multiple new aircraft to its fleet following its merger, favoring fleet diversification. Meanwhile, although United's fleet is more diverse than American's, its recent buying philosophy is actually closer to its Fort Worth-based rival. United was the last of the three to order the A321neo, and it's actively deferred its longstanding A350 order in favor of adding more 787s, with many speculating that the airline will eventually cancel the order.

American Airlines' Fleet Issues

All three airlines have differences in their fleet structures, and Delta's buying philosophy has generally been much different from that of American and United. Notably, however, American has been experiencing some cost issues related to the fleet, but this isn't necessarily because of its focus on fleet simplicity. Instead, the airline's fleet-related cost issues mainly stem from a high debt load, as well as the exact make-up of its fleet, rather than the fact that it consolidated to four types and 11 variants.

American accumulated a significant debt load from its massive 2011 order for over 400 narrowbodies, and it later embarked on hugely expensive fleet retrofit projects later in the 2010s. In addition, it received a significant number of A321-200s and 737-800s during this time period, along with some A319-100s. These planes are inefficient compared to the more modern airliners on sale today, yet they're not particularly old. American's large fleet of smaller A319-100s and 737-800s also isn't ideal for its fleetwide per-seat costs.

Note: Figures do not include narrowbodies with lie-flats or in non-standard layouts

Delta also received a large number of A321-200s and 737NGs in the 2010s, but it notably ordered the larger, more economical 737-900ER rather than the 737-800. Its purchase of 717s was made under unique circumstances, while the A220s offer significantly more attractive costs than an A319. United, meanwhile, took fewer last-generation aircraft during the 2010s, and although it has built up a large 737 MAX 8 fleet, it's generally focused more on larger variants of the 737 MAX and the A321neo.

How The US Carriers Will Evolve Their Fleets

The next narrowbody aircraft for all three carriers will be the Boeing 737 MAX 10. The plane won't specifically replace any one aircraft type, but it will help Delta and United phase out older aircraft types. Both airlines are looking to retire their A319s, A320s, and 757s, while Delta is also looking to phase out its 717 fleet. For United, the narrowbody fleet will be composed of the 737NG, 737 MAX, and A321neo, while Delta will also fly the A220 and A321 long term. American, meanwhile, won't retire the A319s and A320s in the near future as its examples are younger.

American has already simplified its widebody fleet, and the only twin-aisle planes that it has remaining on order are more 787-9s. Although an RFP has been issued for new planes, a firm order has yet to be placed. Delta will begin taking the Airbus A350-1000 in 2027 and plans to retire the Boeing 767-300ER by the end of the decade, while it will start taking the Boeing 787-10 in 2031. Meanwhile, United has a massive number of 787-9s and 787-10s on order, which will be used to replace all 767s and older 777-200s/777-200ERs.

On the narrowbody side, American's fleet will remain more or less the same as today, but with the 737 MAX 10 added, while Delta and United will simplify. On the widebody side, American's fleet is set to remain the same as today, pending the placement of its upcoming order, while United will be simplifying to the 787 and younger 777s. Meanwhile, Delta's widebody fleet will remain quite diverse, with only the 767-300ERs set to leave within the next few years, while the airline will add the A350-1000 in 2027 and the 787-10 in 2031.