The ten biggest leasing companies own over five thousand aircraft.
Number of aircraft owned by company:
GECAS 1,271
AERCAP 1,121
AVOLON 572
SMBC AVIATION CAPITAL 437
NORDIC AVIATION CAPITAL 404
BBAM 404
DAE CAPITAL 334
BOC AVIATION 299
AIR LEASE CORPORATION 278
AVIATION CAPITAL GROUP 274
Source: Airfinance Journal
https://www.airfinancejournal.com/Magazine It's not public knowledge how many of each airlines airplanes are leased, but if you look at the leasing companies web sites, practically every airline is a customer. Airline leasing is particularly popular with the budget airlines like Spirit, Frontier, and Easyjet.
Overwhelmingly, the most popular airplanes by the leasing companies are A320 and 737 and they buy these two aircraft in huge orders of over one hundred at a time which gives them large discounts with Boeing and Airbus.
Many banks are getting into the aircraft leasing business particularly the Chinese and Japanese banks because they realize that very little knowledge about aircraft is needed, you just need a large amount of money to invest. It's not hard for a Japanese bank to buy 100 A320 and 737's and find airlines willing to lease them, particularly in Asia, Latin America, and Europe.
Ireland is headquarters for nine of the ten largest leasing companies. I believe this is mainly because their accounting rules allow aircraft to be depreciated over only eight years. In reality aircraft can safely fly for 30 years in fact Delta doesn't retire their aircraft until they reach 30 years old.