The U.S. derivatives markets regulator is preparing a proposed rule for automated trading, a senior regulator said, after earlier asking market participants for insights on a long list of questions. “I understand that Commission staff is starting to work on a proposed rule,” Scott O’Malia, a member of the Commodity Futures Trading Commission, said in a speech. The CFTC, which regulates futures and swaps markets, in September put out a study – known as a concept release – into computerized trading that was seen as a possible first step toward drawing up formal rules.