Top regulators from the United States and the European Union discussed reforms for futures and over-the-counter derivatives as they toured the world’s largest exchange on Tuesday and lunched with a group of Chicago futures traders and exchange executives.

Gary Gensler, chairman of the U.S. Commodity Futures Trading Commission, and Michel Barnier, the 27-country EU’s financial services chief, discussed concentration in commodity markets and the role of position limits, among other issues.

“I came to Chicago to understand better how these markets are functioning,” Barnier said after touring the Chicago Mercantile Exchange and Chicago Board of Trade’s combined trading floors with CME Group Inc. CEO Craig Donohue.

They had earlier met with IntercontinentalExchange Inc. CEO Jeffrey Sprecher and Chicago Climate Exchange head Satish Nandapurkar.

Barnier said he expected to launch a public consultation early next year before legislating Europe’s first position limits by mid-2011. The CFTC is also working on rules that will expand position limits in the U.S. so they apply to a wider range of commodities and swaps.

“I’m interested in these position limitations in volume, and also in the idea that they can be extended in time,” Barnier said, speaking through a translator. “I am concerned by the consequences of hyperspeculation, especially in agricultural commodities.”

Barnier met U.S. Treasury Secretary Timothy Geithner last week in Washington to discuss capital and liquidity standards for banks.