It's inevitable that with the passage of time, fleet sizes will change. With this change comes a shift in the rankings of the world's largest fleet sizes. With some airlines sending their jets into early retirement, the coronavirus pandemic has been a huge factor in the changing of fleet sizes in recent months. Here are the five biggest airline fleets in 2020 according to Planespotters.net.

It should be noted that numbers exclude aircraft that belong to regional affiliate airlines. While the livery may closely match that of mainline aircraft, regional fleets belong to a separate corporate entity.

American Airlines

The largest fleet in the world belongs to American Airlines, with 872 aircraft. This includes 328 Boeing 737s as well as 418 Airbus A320-family aircraft - includes the A319, A320, and A321. With its headquarters in Dallas, Texas, the average age of the carrier's fleet is 10.8 years old.

Delta Air Lines

The world's second-largest fleet belongs to Atlanta-based Delta Air Lines. The carrier has a fleet of 844 aircraft with an average age of 14.5 years. The most aircraft of a single type would be the Boeing 737, with 217.  For Airbus A320-family aircraft, Delta has 219 jets.

Delta has a much more diverse fleet than its rivals, United Airlines and American Airlines. While the latter has retired its Boeing 757s and 767s, Delta is holding on to its own for the time being. Delta also has the Boeing 717, Airbus A220, and Airbus A350 - all types that are absent from American and United fleets.

Delta Air Lines grounded planes
The airline did see a slight increase in revenues in Q4 compared to Q3. Photo: Getty Images

United Airlines

In third place we have United Airlines with 810 aircraft. The United fleet is slightly older overall than its domestic rivals, with an average age of 15.9 years. The carrier has a whopping 350 Boeing 737s as well as 183 Airbus A320-family aircraft. With 96 Boeing 777s, United has the highest number of this particular Boeing widebody of any US carrier. It also has the most 787 Dreamliners at 55, compared to American Airlines' 44.

United airlines aircraft parked
The flight attendants say that the actions of United are not in accordance with the law. Photo: Getty Images

Southwest Airlines

Southwest Airlines, the carrier based out of Dallas Love Field, is an all-Boeing 737 fleet. Whether planned or out of sheer coincidence, the airline currently is listed as having 737 jets in its fleet (595 in service and 142 parked). Of course, many of the parked aircraft will be the Boeing 737 MAX aircraft, which are currently working towards FAA recertification.

The average age of Southwest's fleet is 12.3 years.

southwest 737 MAX
The MAX is almost ready for its test flights, according to the Federal Aviation Administration. Photo: Getty Images

China Southern Airlines

Finally, in fifth place is Chinese carrier China Southern. The Guangzhou-based carrier has 616 aircraft - including the Airbus A380 superjumbo. In fact, it's the only carrier in China (and on this list) to have the A380 as part of its fleet.

China Southern has 213 Boeing 737s, as well as 281 Airbus A320-family aircraft.

The average age of China Southern's fleet is just 7.4 years.

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Wuhan Airport is currently closed for all flights. Photo: China Southern

What do you think of the numbers and the airlines that made the list? Was it what you had expected? Let us know in the comments.