Nigerian office workers at a subsidiary of the U.S. oil company ExxonMobil have started a strike over a pay dispute.  The work stoppage adds to supply concerns in Nigeria's oil sector as Gilbert da Costa reports for VOA from Abuja.

An unidentified youth with a Shell Oil uniform walks towards his shop in Port Harcourt, Nigeria, 17 May 2007

The group representing senior oil employees in Nigeria, the Petroleum and Natural Gas Senior Staff Association (PENGASSEN) says negotiations over wages and working conditions broke down Wednesday.

Union national president Peter Esele says talks resumed hours after the strike began.

"Right now, we are still talking," he said.  "A line of communication is about to be opened now, bt right now I cannot say anything to the media.  I do not want to make a comment until we see how events will go."

Union officials warn the strike at Mobil Producing Nigeria could cripple oil exports if not resolved quickly.  But the company is playing down such fears, insisting there is no disruption to its oil production of 780,000 barrels per day. 

Mobil is the second-largest oil company in Nigeria, after Royal Dutch Shell.  Oil companies in Nigeria have seen a fall in production, because of militant attacks in the Niger Delta.

In the past, strikes declared by PENGASSEN and its sister union, the National Union of Petroleum and Gas Workers, have delayed some of Nigeria's oil exports, the eighth-largest in the world.

Analysts warn new concerns about disruptions in Nigeria could trigger even higher world oil prices.

About 500,000 barrels per day of Nigeria's daily oil output cannot be accessed, because of security issues in the Niger Delta.