More than 100 foreign oil workers have been kidnapped in the creeks that form the Niger Delta in recent times - although the hostages are normally released after a ransom has been paid. Kidnappers always deny that they have released workers, however.
The militant groups behind the attacks say that they want a larger share of oil revenues and also want to see the release of two leaders currently under arrest on charges of money laundering and treason.
Oil workers, demanding welfare benefits, have just completed the second day of strike action in Nigeria - and these factors appear to be driving up the price of oil, as supply worries continue.
London crude climbed by 28 cents to $71 a barrel this afternoon (Friday) - after reaching a nine-month high of $71.80 yesterday.
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