Oil crept up this morning after falling a day earlier when the release of several foreign workers seized in Nigeria's Niger Delta allayed concerns over further disruptions.
London Brent crude, currently seen as the most representative of global oil prices, was up 30 cents at $66.35 a barrel by earlier this morning.
It fell 20 cents yesterday 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 8 cents to $63.27 a barrel.
Militant attacks in Nigeria, the world's eighth-largest oil exporter, have escalated in the past year and 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 yesterday the Forcados oil export terminal in Nigeria may resume operations in June, more than a year after it was shut by militant attacks.
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's shutdown of a 115,000-bpd crude unit at its Singapore refinery for an indefinite period due to a fire.