Global oil prices dropped after tensions eased in the Middle East and North Africa allaying fears of supply disruptions.
North Sea Brent crude oil prices for delivery in November hovered around $109. Brent lost 3.6% for the week as a whole and is on track to log its sharpest decline since mid-June.
Benchmark US crude oil prices for delivery in October ended $1.72 lower at $104.67, Reuters data showed.
Brent had earlier traded at $112 per barrel while US crude traded at $108.21 a barrel.
The likelihood of US military intervention in Syria fading, supply resumption in Libya and signs of a softening Iran all contributed to the price drop.
Meanwhile, more than a third of Libya's crude production is back on stream.
Strikes over pay had hampered oil production and exports from Libya, which accounts for over 1.5% of global oil output. Prime Minister Ali Zeidan's government estimated the country was losing about $130m (£81m, €98m) in oil revenues each day.
"If this is not yet another fake-out with Libya, it could be a turning point and start to act as a short-term cap on oil prices," Dominick Chirichella, an analyst at the US-based Energy Management Institute wrote in a research note.
Iran and Libya are members of the 12-nation Organisation of the Petroleum Exporting Countries (Opec), which accounts for the bulk of the world's oil exports.
Fed Stimulus Push
Earlier, oil prices gained on news that the US Federal Reserve had delayed tapering its $85bn bond-buying stimulus.
Brent crude for delivery in November finished at $110.60 a barrel in London trade on 19 September.
New York's main contract, the West Texas Intermediate for delivery in October, gained $2.65 to finish at $108.07 a barrel on 18 September.