U.S. oil prices recorded their eighth consecutive week of falls, 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.
U.S. oil futures fell below $40 a barrel for the first time since 2009 on Friday before settling down 87 cents, or 2.11 percent at $40.45 a barrel.
Baker Hughes also said that U.S. weekly rig counts rose for the fifth straight week, increasing by 2 to 674. Last year, U.S. oil rigs totaled 1,564.
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.
Asian and European stocks followed Wall Street lower as fears took hold of a China-led slowdown in global growth.