U.S. oil prices headed for their eighth consecutive week of falls on Friday, the longest losing streak since 1986, after a sharp drop in Chinese manufacturing increased worries over the health of the world’s biggest energy consumer. Activity in China’s factory sector shrank at its fastest pace in almost 6-1/2 years in August as domestic and export demand dwindled, adding to worries about lower consumption of crude in the second-biggest oil user. Both global oil benchmarks are near 6-1/2-year lows, with U.S. crude heading for its longest weekly losing streak in 29 years.