Applications to U.S. graduate schools from international students surged in 2011, reaffirming the strength of American institutions in an increasingly competitive market for prosperous foreign students, according to an annual survey by the Council of Graduate Schools.

America’s flagship public universities depend on a growing population of international students to supply the revenue they no longer get from their states. Out-of-state students pay two or times as much as residents to attend public institutions. Foreign students tend to come from prosperous families in China, India or South Korea and to pay full fare, a quality that makes them desirable to public and private colleges alike.

Those students covet an American education. Growing demand has spawned a cottage industry of agents who earn thousands of dollars in finder’s fees for delivering students to American schools, employing methods that have drawn criticism from inside and outside academia.

Chinese and Indian universities covet those students, as well, and a collegiate building boom in those nations has succeeded in luring some of them away. China and India are investing heavily in higher education at a time when America and Britain are perceived to be pulling money out, at least in terms of government subsidies.

International applications have risen in each of the past six years; but the 11-percent bump from 2010 to 2011 is the largest since 2006.

China is the engine driving the increase: applicants from China rose 21 percent in 2011, compared to an eight-percent increase in India and 2 percent in South Korea, the second- and third-leading supplier of foreign students to American schools.

Offers of admission rose, as well. The survey does not report on how many admitted students actually chose to attend, presumably a more telling measure.