Oil fell below $64 a barrel today, extending declines that followed Iran's release last week of 15 British sailors and marines.
The two-week detention of the UK military personnel by Iran had driven US crude oil prices above $68 a barrel, their highest since September last year.
US crude fell 45 cents to $63.83 a barrel by earlier this morning. London Brent crude was down 23 cents at $68.01. Brent maintained a more than $4 premium over US crude partly because of more plentiful supplies of US crude relative to Brent. Trading was subdued because much of Europe is shut for the Easter Monday holiday.
The release on Thursday of the British sailors and marines has eased fears of an increase in tensions between the West and Iran, the world's fourth biggest oil exporter.
But concerns about Iran's uranium enrichment programme as well as the conflict in Iraq remain a big factor underpinning oil prices, which are well above this year's lows of $49.90 a barrel in January.
"'Iranium' remains a hot issue and, as importantly, the lack of an Iraqi solution will continue to haunt the Middle East for months to come," said Olivier Jakob, from oil industry consultancy Petromatrix.