Brent and U.S. crude futures tumbled on Friday to the lowest settlement prices in months, as oversupply in the Atlantic basin and low demand outweighed worries over political tensions in the Middle East, North Africa and Ukraine.
Oil prices ended the week down more than 3 percent, as forecasts for a supply glut in West African and European markets dragged Brent below $105 a barrel and U.S. crude below $98.
"Since June 23, the market's been going down," said Andy Lebow, vice president at Jefferies Bache in New York. "This looks like an extension of a pretty significant bear market."
Brent crude slid $1.18 to settle at $104.84 a barrel, its lowest settlement since April 2.
U.S. crude fell 29 cents to settle at $97.88 a barrel, the lowest settlement since Feb. 6. U.S. crude notched its biggest weekly decline since January, almost 4.5 percent.
U.S. crude's discount to Brent <CL-LCO1=R> closed at $6.96.
U.S. RBOB gasoline prices led the complex lower, settling at $2.7443 a gallon, then fell more in post-settlement trading, hitting the lowest since February.
Putting additional pressure on the market, an outage at the 115,000-barrel-per day Coffeyville, Kansas, refinery, a major crude consumer, could last up to four weeks.
The front of the Brent futures price curve is trading at a heavy discount to later barrels in a formation known as a contango. This discount has now lasted longer than any since early 2011, reflecting "weak physical demand and an oversupplied Atlantic Basin," Morgan Stanley analyst Adam Longson said.
Meanwhile, worries over geopolitical risks to oil supply have eased despite escalating violence in parts of the Middle East and North Africa.
OPEC's second largest producer, Iraq, is battling an Islamic insurgency in the north and west. The conflict threatens to split the country, but has yet to have an impact on near-record oil exports from the south.
Baghdad is also embroiled in a dispute with Iraqi Kurdistan over oil exports via Turkey.
In Libya, oil output remains steady around 500,000 bpd, down from 1 million bpd in 2012, following weeks of clashes between rival militias.
Energy investments in Russia also faced delays after sanctions imposed by the United States and European Union limited access to funds.
Oil prices hardly moved after data showing U.S. job growth slowed more than expected in July. Non-farm payrolls increased only by 209,000 last month, after surging by 298,000 in June, the Labor Department said on Friday.
(By Anna Louie Sussman; Additional reporting by Rowena Caine in London, Florence Tan in Singapore; Editing by Christopher Johnson, Lisa Von Ahn, Tom Brown and David Gregorio)