The World’s Largest In-service Jet Fleets at the end of 2011 is shown below:
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Source: Current Market Outlook 2012-3031, Boeing
With over 6,000 jets, the U.S. has the largest jet fleet (with over 30 seats) followed by China. There are reasons for the high number of jets in-service in the U.S. some of which include the vast distances between cities, high population, lack of efficient alternative transportation options for travel, huge state subsidies showered upon the pathetic airline industry, etc. The difference between the U.S. and other countries is striking as well with all the other countries having less than 1,000 jets in service.