By Robert Gibbons
NEW YORK (Reuters) - Oil prices fell on Friday and headed for their fourth straight weekly declines as weak economic data from China and a rise in U.S. oil drilling rigs added pressure.
U.S. energy firms added 21 oil rigs this week after pulling seven rigs last week, oil services company Baker Hughes Inc said in its weekly report.
The rig count data arrived a day after U.S. crude fell into bear market territory, with its $48.45 a barrel settlement off 21 percent from the June 10 close at $61.43. A 20 percent downturn is considered by many traders to constitute a bear market.
China's factory sector contracted in July by the most in 15 months, a preliminary private survey showed. The weaker-than-expected result followed a stock market slide that began in June.
Brent September crude was down 65 cents at $54.62 a barrel at 1:43 p.m. EDT (1743 GMT), having dropped to $54.30, the lowest front-month price since April 2.
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U.S. September crude fell 47 cents at $47.98. The session low of $47.72 was the lowest price since April 1.
"Crude was already lower on concerns about the global economy and the rig count added to the negativity," said Phil Flynn, analyst at Price Futures Group in Chicago.
The world's top oil companies are set to report second-quarter earnings showing another drop in profits that could force more spending cuts, according to analysts.
The dollar's strength also applied pressure, as a stronger U.S. dollar makes greenback-denominated oil more expensive for consumers using other currencies.
Brent and U.S. crude have posted double-digit losses in July. With U.S. crude off more than 19 percent, it could challenge the 19.4 percent loss in December, which was the biggest monthly slump since the financial crisis in 2008.
Signs of economic slowdown in China have pressured oil and metals, with industrial feedstock copper slumping to the lowest levels in six years.
Demand for gasoline has been strong, keeping refineries churning at high utilization rates, but August U.S. RBOB gasoline futures made a decisive move below its 200-day moving average of $1.8514 a gallon on Friday.
"This looks like profit-taking as the end of the U.S. driving season gets closer," said Gene McGillian, analyst at Tradition Energy in Stamford, Connecticut.
Set for a 5 percent weekly drop, it would be gasoline's biggest since mid-March and a sixth consecutive weekly slide, most since the seven weeks ending Jan. 9.
(Additional reporting by Amanda Cooper in London; Editing by Marguerita Choy)