Oil prices fell to their lowest since the third quarter of 2017 today, heading for losses of more than 11% in a week.
Global oversupply is keeping buyers away from the market ahead of the long festive Christmas break.
Brent crude fell $1.56 to a low of $52.79 a barrel, its weakest since September 2017, before rallying to trade around $53.10, down 11.9% on the week, this afternoon.
US light crude oil CLc1 was down 60 cents at $45.28, on course for a decline of 11.6% for the week.
Crude has lost ground along with major equity markets as investors fret about the strength of the global economy heading into next year.
The prospect of a possible government shutdown in the US, the world's biggest oil consumer, added to investors' worries.
Falls were exaggerated by thin trade and risk aversion ahead of Christmas and the New Year holidays, traders said.
Since reaching multi-year highs at the beginning of October, both crude oil benchmarks have lost more than a third of their value in their steepest collapse for three years.
Driving the sell-off has been sustained oversupply as the US has emerged as the world's biggest crude producer thanks to the success of its shale industry.
The US now pumps 11.6 million barrels per day (bpd) of crude, putting it ahead of Saudi Arabia and Russia.
The big oil producers in the Organization of the Petroleum Exporting Countries, dominated by Middle East Gulf states, have agreed to reduce production to try to push up prices.
But those output cuts - a reduction with Russia and other non-OPEC producers of 1.2 million bpd - do not kick in until next month, and meanwhile global inventories are filling up fast.
In an effort to show its commitment to reducing supply, OPEC will release a table detailing output cut quotas for its members and allies such as Russia, OPEC Secretary General Mohammad Barkindo said in a letter reviewed by Reuters.
To reach the proposed cut of 1.2 million bpd, the effective reduction for member countries was 3.02%, Barkindo said.
That is higher than the initially discussed cuts of 2.5% as OPEC seeks to accommodate Iran, Libya and Venezuela, which are exempt from any requirement to cut.