Oil prices fell sharply on Monday, extending heavy losses seen last week caused by poor jobs data in the United States, the world's biggest energy-consuming nation.
Prices slumped despite a new pipeline attack in Nigeria, an important exporter of oil.
In London, Brent North Sea crude for delivery in August dropped 1.73 dollars to 63.88 dollars a barrel.
New York's main contract, light sweet crude for August delivery, shed 1.58 dollars to 64.05 dollars a barrel.
"People are starting to wonder about the strength of the US economic recovery... This does not look good for oil demand because it means that consumer spending will remain weak."
A closely watched US Labor Department report last week showed US job losses had surged more than expected to 467,000 in June, pushing the unemployment rate to a new 26-year high of 9.5 percent.
The report, seen as one of the best indicators of economic momentum, reversed the improvement seen the previous month when job losses fell to 322,000.
Crude futures slid on Monday despite fresh unrest in Nigeria. Nigerian militants on Monday said they destroyed a Chevron oil pipeline junction in the latest attack on Nigeria's key money earner since the government offered an amnesty.
The Movement for the Emancipation of the Niger Delta (MEND) said it attacked the Okan manifold installation late Sunday.
According to the rebels, the manifold controls about 80 percent of the crude that Chevron Nigeria Limited sends to its BOP Crude Loading Platform.
A Chevron spokesman said an investigation had started and no comment would be made.
President Umaru Yar'Adua on June 25 offered an amnesty to any rebel in the Niger Delta, the main oil region, who lays down his arms. The government has said the amnesty offer, which starts August 6, also applies to detained MEND leader Henry Okah.
But MEND, which says it is fighting for a fairer distribution of the Delta oil wealth, has claimed at least four attacks since the offer was made.
MEND is the strongest of a series of groups fighting in the Niger Delta since 2006. The unrest has reduced Nigeria's exports to 1.8 million barrels per day from 2.6 million three and a half years ago.
Source: AFP Global Edition