Bernie Dan, chief executive of the Chicago Board of Trade, is doing such a good job of maintaining a wall of silence about who might buy the exchange that one man has taken measures to winkle out the truth.

John Lothian, a broker who runs a widely read online newsletter, has launched a daily online poll inviting his readers - among the best brains in the industry - to guess who wants to buy the exchange, which started in 1848 trading hay and flour.