Delta Air Lines carried the most scheduled passengers last year, according to the International Air Transport Association, while Ryanair topped the list for international scheduled passengers only. 
Total (International + Domestic)
Rank Airline Thousands
1 Delta Air Lines 116,726
2 Southwest Airlines 112,234
3 United Airlines 92,619
4 American Airlines 86,335
5 China Southern Airlines 86,277
6 Ryanair 79,649
7 China Eastern Airlines 79,611
8 Lufthansa 64,393
9 US Airways 54,238
10 Air France 50,636
International
Rank Airline Thousands
1 Ryanair 79,649
2 Lufthansa 50,877
3 easyJet 44,601
4 Emirates 37,733
5 Air France 33,693
6 British Airways 31,273
7 KLM 25,775
8 United Airlines 24,843
9 air berlin 23,179
10 Turkish Airlines 22,381
