The price of US crude oil sank below $55 a barrel on Friday afternoon, a level last seen in June 2005, amid concerns over the full implementation of a recent cut in OPEC oil output.
New York's main contract, light sweet crude for delivery in December, plunged $1.40 to $54.86, though it later recovered to $55.50.
That marked the lowest point since June 14, 2005, before Hurricane Katrina had devastated US Gulf Coast energy facilities and sent crude futures to then-record levels.
The contract had plunged $2.50 on Thursday as traders reviewed conflicting reports on exports from the OPEC. In London, Brent North Sea crude for January delivery fell one cent to $58.53, having earlier hit a one-year low of $57.85.
The 11-member OPEC cartel decided last month to slash output by 1.2 million barrels per day (bpd) to 26.3 million bpd from November 1, to put a floor under prices which have tumbled from above $78 in July and August this year.
One report said OPEC's exports had fallen by 1.1 million bpd, but another claimed they had actually risen in the last month, leading analysts to question whether the cartel would deliver on its output cut pledge.
