Chicago Mercantile will tighten floor surveillance.

The exchange’s move is an attempt to mollify critics who have complained of trading abuses. The exchange also announced that it had hired Paul B. O’Kelly, an assistant regional administrator in the Chicago office of the Securities and Exchange Commission, to become the exchange’s new president for compliance. Plans call for hiring eight investigators for the exchange’s compliance department, increasing the total number to 44. The new workers would include three floor investigators, the first permanent investigators assigned exclusively to the trading floor.