Prof. Sidney Culbert of the University of Washington estimated 1 million to 2 million fluent Esperanto speakers about a decade ago. He is the only person I've h

Prof. Sidney Culbert of the University of Washington estimated 1 million to 2 million fluent Esperanto speakers about a decade ago. He is the only person I've heard of who has done actual research (he produced the number-of-speakers figures for some 100 languages for the World Almanac). Some methodology at http://www.panix.com/~dwolff/docs/culbert-methods.html http://www.panix.com/~dwolff/docs/culbert-methods.html.