Will add rank (or you may add) by attendance, size, number of countries participating, date, categories : blank(pre-BIE), BIE - 6 month, BIE - 2nd category - 3 month, do rank by your appeal or interest. Smaller named international fairs may be added for interest, but please do try to include in order: year, attendance official, number of countries participating, acres of grounds, square feet(meters) enclosed, city-region, state, country, short name, official name, BIE category. Enjoy and feel free to improve data and add information, do try to cite source. If you do not know info, then try to add what you can and maybe someone else or you may find out more and add it latter.
http://www.ranker.com/list/world-fairs-and-expositions-v1/dtlarch,
Expo 2010 Shanghai China
World's Fair 1964-5, New York, USA
World's Fair 1939-40, New York,
Expo 1970, Osaka, Japan
Expo 1967, Montreal, Canada
Expo 1900, Paris, France
Expo 1889, Paris, France
World's Fair 1893, Chicago, USA
Expo 1958, Brussels, Belgium
Expo 1851, London, England