Global oversupply, huge stockpiles and refinery shutdowns have led to plunging prices for US crude oil.
It tumbled by 3 percent on Thursday and by Friday morning hit its lowest in almost six and a half years at 41.35 dollars a barrel.
Brent crude traded at 49 dollars a barrel, down 22 cents but still some way off the 45.19 dollars per barrel it touched at the start of the year.
US crude is much weaker than the North Sea benchmark partly due to a spate of refinery outages that have sapped US demand.
Analysts believe prices could fall further with the latest price drop not enough to put the brakes on the US supply growth.