Oil prices slid lower Monday, with Brent hitting a four-year low, on oversupply worries heightened by OPEC signals that producers have no intention of cutting output.
The International Energy Agency added to bearish sentiment by lowering its outlook for demand in its October report, citing weak global economic growth.
US benchmark West Texas Intermediate for November slipped eight cents, closing at $85.74, the lowest price since December 2012.
Brent North Sea crude for delivery in November, the international benchmark, dropped $1.32 to close at $88.89 a barrel in London trade, its lowest level since late 2010.
The market took on a "bearish tone" after recent comments from some members of the Organization of the Petroleum Exporting Countries showed complacency with the oversupply situation, said Matt Smith of Schneider Electric.
OPEC kingpin Saudi Arabia indicated it was "comfortable with price around $90," he said, adding that apparently "they are more about market share than price."
Iraq became the latest OPEC crude exporter to cut its prices after similar moves by Saudi Arabia and Iran.
"OPEC is still giving no indication that it might take steps to shore up prices," Commerzbank analysts said in a research note.
"Iraq is now the third important OPEC member to significantly lower its sales prices as compared with the international benchmarks," they added.
However, Kuwaiti Oil Minister Ali al-Omair said Sunday that he expects falling prices to recover during the Northern Hemisphere winter -- but OPEC was unlikely to counter the slide in the short term.
"We expect (oil prices) to increase in the winter season or at least preserve its current level," said Omair, cited by the official KUNA news agency.
The minister also said he believes that oil will not drop below $76-77 a barrel, which is the production cost in Russia and the United States.
The decline was expected due to geopolitical factors, a rise in supplies and negative forecasts for global economic growth, according to Omair.
He said Kuwait has not received any invitation for an emergency OPEC meeting to discuss prices but would attend if one were scheduled.
Venezuela on Friday said it would request such an emergency OPEC meeting.
"We are going to ask for an extraordinary OPEC meeting," said Foreign Minister Rafael Ramirez, who is the nation's former oil minister and ex-head of the public oil company PDVSA.
"We need to try to coordinate some sort of action to stop falling oil prices," he added.