NEW YORK (MarketWatch) -- Shares of petroleum producers fell back from two-year-highs on Friday, as equities and commodities markets in the U.S. reacted to a steep sell-off in China's stock market. The NYSE Arca Oil Index (XOI 1,134, -8.09, -0.71%) fell 1% to 1,131. The NYSE Arca Natural Gas Index (XNG 575.10, -5.63, -0.97%) dipped 1% to 575. The Philadelphia Oil Service Index (OSX 225.01, -3.32, -1.45%) dropped 1.5% to 225. Among movers, Massey Energy (MEE 47.25, +0.23, +0.49%) rose 1% to $47.49 and Anadarko Petroleum (APC 63.67, -1.57, -2.41%) fell 2.2% to $63.84. Crude-oil prices dropped 1.6% to $86.46.
