Oil fell more than 6% in price to below $US70 per barrel on Thursday to a 15-month low.
Inventories in the United States are rising amid concerns of a possible recession.
US crude settled at $US69.85, down $US4.69, after sliding as low as $US68.57 - the lowest level since 27 June, 2007.
In London, November Brent crude, which expires on Thursday, settled at $US66.32, down $US4.48.
Crude oil inventories in the United States rose 5.6 million barrels last week, as demand continued to fall.
The Energy Information Administration reported gasoline inventories rose 7.0 million barrels. Demand over the past four weeks dropped 8.9% from the levels a year ago.
US crude prices have dropped nearly a third in three weeks, since setting of record of $US147.27/b on 11 July.
The Organization of the Petroleum Exporting Countries said on Thursday it had brought forward an emergency meeting to discuss the impact of global recession on oil markets to Friday next week.
