Oil prices have fallen below $90 for the first time this month with Opec expected to increase output next week.
Concerns that a pipeline fire in the US would disrupt supplies have also faded.
A barrel of light crude fell $2.3 to end at $88.71 in New York, far below its $99 high seen on 21 November. Brent crude fell $1.96 to $88.26 in London.
Traders are focused on an OPEC meeting next week in Abu Dhabi, where the 12-member cartel is expected to decide whether to increase production.
Several ministers from Opec nations have said in recent days that the group is ready to boost output to bring prices down.