By Greg Ryan

Law360, New York (July 19, 2011, 2:49 PM ET) -- A Nevada federal judge ruled Monday that state claims against natural gas companies in multidistrict litigation alleging they conspired to artificially inflate prices are preempted because the Federal Energy Regulatory Commission has jurisdiction over the price-reporting practices at issue.

U.S. District Judge Philip M. Pro's decision released American Electric Power Co. Inc., Williams Co. Inc., Xcel Energy Inc. and other defendants from the long-running litigation, though some companies still face federal antitrust claims.

The plaintiffs alleged the defendants — either directly or through affiliates — manipulated...