Benchmark West Texas Intermediate crude for November delivery fell 16 cents to close at US$102.87 a barrel on the New York Mercantile Exchange.
For the week, the price declined $1.80 a barrel.
Oil has fallen for three straight weeks as diplomatic efforts surrounding Syria and Iran ease concerns about Middle East supplies. That's outweighed some positive economic news in the United States.
Brent crude, the benchmark for international crudes used by many U.S. refineries, dropped 58 cents to US$108.63 a barrel Friday on the ICE Futures exchange in London.
In other energy futures trading on Nymex, wholesale gasoline fell three cents to US$2.68 a U.S. gallon (3.79 litres), heating oil lost one cent to US$2.99 a gallon and natural gas rose two cents to $3.59 per 1,000 cubic feet.
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