shares of pioneer natural resources co pxd shed 686 to 18185 wednesday on what proved to be an allaround poor trading session for the stock market with the sp 500 index spx falling 070 to 389193 and dow jones industrial average djia falling 087 to 3187457 this was the stocks eighth consecutive day of losses pioneer natural resources co closed 10661 short of its 52week high 28846 which the company achieved on may 31st the stock demonstrated a mixed performance when compared to some of its competitors