shares of valero energy corp vlo slipped 158 to 6546 thursday on what proved to be an allaround poor trading session for the stock market with the sp 500 index spx falling 016 to 447375 and dow jones industrial average djia falling 018 to 3475132 valero energy corp closed 1949 short of its 52week high 8495 which the company reached on june 3rd the stock underperformed when compared to some of its competitors thursday as phillips 66 psx fell 041 to 6576 marathon petroleum corp mpc fell 079 to 5910 and hollyfrontier corp hfc fell 106 to 3072 trading volume 23 m remained 16 million below its 50day average volume of 39 m editors note this story was autogenerated by automated insights an automation technology provider using data from dow jones and factset see our market data terms of use