Oil crept up on Friday after falling a day, as the release of several foreign workers seized in Nigeria's restive oil-producing Niger Delta allayed concerns over further disruptions to its production.
London Brent crude, currently seen as the most representative of global oil prices, was up 13 cents at $66.18 a barrel. It fell 20 cents on Thursday, after the Movement for the Emancipation of the Niger Delta freed eight of the 18 workers seized in three attacks.
US light crude boosted recently by worries over thin gasoline supplies as the summer driving season looms, gained 6 cents to $63.25 a barrel. "There is nothing happening aggressively to push prices up or down at this juncture, but with Nigerian and Iranian issues in the background, prices are still over $60 a barrel," said Gerard Rugby, a Sydney-based consultant from Fuel First Consulting.
Militant attacks in the world's eighth-largest oil exporter, which have escalated in the past year, have shut daily output of about 600,000 barrels, or a fifth of production capacity.
But analysts believe the region's volatility has already been priced into the market. Supply fears also eased after Royal Dutch Shell said on Thursday the Forcados oil export terminal in Nigeria may resume operations in June, more than a year after it was shut by militant attacks.
Shell declined to give a clear date to restore production fully. A restart would add to supply of Nigerian crude, prized by refiners, as it is easy to process into transport fuels.
Brent crude is up around 9 percent this year on geopolitical supply worries, and is trading at a strong $3 premium to US crude, which is weighed down by swollen supplies at its Cussing, Oklahoma delivery point.
Crude storage capacity at Cussing should rise from 40 million barrels now to 50 million barrels by 2009, according to oil major BP Plc, traditionally a large holder of Cussing storage.
Refinery shutdowns in the Midwest and limited pipeline capacity to take crude oil from Cussing to the Gulf Coast are also major factors in US crude's recent weakness.
In Europe, worries over refinery shutdowns in Belgium that created fears over gasoline supply disruption were dispelled after a potential strike in Antwerp was averted. But Asia-Pacific fuel markets could still be tightened by Exxon Mobil Corp's shutdown of a 115,000-bpd crude unit at its Singapore refinery for an indefinite period due to a fire.