Brent crude fell on Monday, dropping below $86 a barrel as worries about booming supply and sluggish demand pushed the global oil benchmark back toward last week's four-year low. U.S. crude hovered below $83 a barrel.
Brent tumbled more than a dollar in early U.S. trade, but bounced off session lows as global equities markets gained.
Oil prices are down more than 25 percent since June on concern about a saturated global oil market and a gloomy economic outlook from Europe to China. Last week, Brent slid below $83, its lowest since 2010.
Energy economists have slashed forecasts of world oil demand growth for next year.
It was also not clear whether the Organization of the Petroleum Exporting Countries will decide to cut output to support prices when OPEC members meet on Nov. 27.
Saudi Arabia, Kuwait and Iran have all indicated reluctance to change supply policy, while Venezuela has requested an extraordinary meeting ahead of the Nov. 27 gathering to discuss how to arrest the price plunge.
Brent fell as low as $84.41, and was down 69 cents at $85.47 a barrel by 1945 GMT. The global benchmark had rallied 2 percent on Friday, its biggest gain in over a month.
U.S. crude settled down 4 cents at $82.71 a barrel.