S&P boosted by energy shares; Nasdaq, Dow flat

U.S. stocks had opened slightly higher, with the Dow briefly crossing the 18,000 mark, as oil prices rose 2.9 percent due to a weaker dollar and hopes for an easing of the oil glut. Oil majors Exxon and Chevron were up about 1 percent and gave the biggest boost to the S&P 500. Fed officials have repeatedly said a hike in June is on the cards.