Oil prices continued to fall on Thursday after inventory data, published on Wednesday, showed that US stockpiles of crude grew for the first time since November.
Prices have been weakened recently due to a rally in the US dollar, but even as the US currency fell on Thursday, there was no support for oil prices.
Data from the American Petroleum Institute indicated that crude oil stockpiles increased by 3.23 million barrels last week, more than the 900,000 barrels forecast by analysts surveyed by Bloomberg.
Many had expected a "build" - an increase - in US invetories in the coming weeks as oil rig counts, as monitored by oilfield services group Baker Hughes, have increased strongly in the past few weeks as crude prices have risen.
Last week, the price of Brent crude, the global benchmark contract, reached a three year high of $71.28 a barrel.
As crude prices rise, more producers bring production online. In the US, production costs are higher - particularly of shale oil and other harder to reach oil reserves - and higher prices mean they can produce more profitably.
Brent crude was down 0.58% at $68.12 a barrel, while Nymex West Texas Intermediate fell 0.53% to $64.16 a barrel.