World's busiest metro/subway systems

The most-used metro systems in terms of passenger rides per year:

Japan Tokyo Subway (Tokyo Metro and Toei Subway only) 3.161 billion (2010)
Russia Moscow Metro 2.348 billion (2010)
South Korea Seoul Subway (Seoul Metro, SMRT and Seoul Metro Line9 Corporation only) 2.173 billion (2009-2010)
China Shanghai Metro 1.884 billion (2010)
China Beijing Subway 1.84 billion (2010)
United States New York City Subway 1.604 billion (2010) [6]
France Paris Métro 1.506 billion (2010) [7]
Mexico Mexico City Metro 1.410 billion (2010)
Hong Kong Hong Kong Mass Transit Railway 1.41 billion (2010)
China Guangzhou Metro (including FMetro) 1.18 billion (2010)
United Kingdom London Underground 1.107 billion (2010)
Japan Osaka Municipal Subway 837 million (FY 2010)
Egypt Cairo Metro 805 million (2009/2010)
Russia Saint Petersburg Metro 777.3 million (2010)
Brazil São Paulo Metro 754 million (2010)
Singapore Singapore Mass Rapid Transit 744.8 million (2010)
Spain Madrid Metro 642 million (2009)
Chile Santiago Metro 621 million (2010)
Czech Republic Prague Metro 578.5 million (2010)
Republic of China Taipei Metro 566.4 million (2011)
Austria Vienna U-Bahn 534.4 million (2010)
Germany Berlin U-Bahn 508.9 million (2009)
Ukraine Kiev Metro 504.3 million (2010)
India Delhi Metro 459.5 million (2010-2011)
Venezuela Caracas Metro 484.6 million (2009)
Iran Tehran Metro 437.3 million (2010)
Japan Nagoya Municipal Subway 427.5 million (2008)
Argentina Buenos Aires Subway 409.8 million (2008)
Greece Athens Metro 388 million (2009)
Spain Barcelona Metro 381.2 million (2010)
Germany Munich U-Bahn 360 million (2010)
Canada Toronto subway and RT 336 million (2010)
Italy Rome Metro 331 million (2008)
Italy Milan Metro 328 million (2007)
Sweden Stockholm Metro 310 million (2010)
Hungary Budapest Metro 297 million (2008)
Canada Montreal Metro 296.3 million (2010)
Ukraine Kharkiv Metro 278 million (2007)
South Korea Busan Subway 274.8 million (2010)
Belarus Minsk Metro 273.6 million (2010) .......................(more)

The complete list is at: http://en.wikipedia.org/wiki/Metro_systems_by_annual_passenger_rides