In London, the price of Brent North Sea crude for June delivery added four cents to 67.69 dollars per barrel in electronic trading.

New York"s main oil futures contract, light sweet crude for delivery in June, fell nine cents to 65.62 dollars per barrel in electronic deals.

Trading was quiet on Tuesday with many Asian and European markets shut for a public holiday, dealers said.

"Crude futures were almost unchanged in quiet trade ... with Japanese and Chinese markets closed for most of the week, while European markets (apart from London) will be shut for the May Day holiday," said Michael Davies, analyst at the Sucden brokerage in London.

However, traders focused on fresh supply concerns in Nigeria, which is the world"s sixth-biggest exporter, accounting for a daily output of some 2.6 million barrels.

As many as six foreign oil workers were kidnapped on Tuesday by unidentified gunmen in an attack on an oil facility off the coast of the southern Bayelsa State, according to a government official.

"This incident has once again highlighted the instability in the region, with the country"s output still below full capacity and the most recent presidential elections have only made the situation worse, with foreign observers saying that votes rigging was commonplace," added Davies.

Oil industry sources in Nigeria said that six foreigners, including four Italians and one U.S. national, had been seized from an oil vessel.

They said the attack happened around 4:00 a.m. (0300 GMT) and that one Nigerian sailor was killed in the incident. There was no immediate confirmation from the Nigerian Navy.

Crude futures had fallen Monday on world markets amid profit-taking after sharp gains last week following news of a possible terrorist plot in key crude producer Saudi Arabia, dealers said.

Prices had surged before the weekend after Saudi Arabia announced it had foiled an attack on oil facilities, which was linked to Al-Qaeda.

Market attention was meanwhile starting to turn to today"s upcoming weekly update on the state of energy stockpiles in key consumer the United States, traders said.

All eyes are on U.S. gasoline or petrol reserves heading into the peak-demand driving season, which kicks off at the end of May, when many Americans take to the roads for their summer holidays.

PIN/AFP