Energy companies down on US economic concerns

** S&P 500 energy index .SPNY falls 4% as oil prices edge lower

** Brent crude LCOc1 down ~1% at $67.32/barrel and U.S. West Texas Intermediate (WTI) crude futures CLc1 down 1% at $63.39/barrel

** Oil prices fall as traders focus more on concerns about the U.S. economy than the start of looser monetary policy after the U.S. Federal Reserve cut interest rates for the first time this year

** Top oil and gas firms Exxon Mobil XOM.N and Chevron CVX.N down 1.2% and 1%, respectively

** EQT EQT.N, Devon Energy DVN.N and APA Corp APA.O fall between 1.5% and 1.7%, among biggest pct loosers on the energy index

** Refiners Phillips 66 PSX.N and Marathon Petroleum MPC.N down 1.6% and 1%, respectively

** Oilfield services cos Halliburton HAL.N and SLB SLB.N both down marginally