The move comes after a car bomb was detonated at the perimeter fence of its Port Harcourt headquarters on Monday. The bomb was in the car park of a residential compound. Nine cars were damaged.
 
Shell staff will stay put and oil and gas production will not be affected, company officials said.
 
Italian oil company Agip has already shifted the families of its workers to Lagos.
 
In February, Shell, the largest oil operator in Nigeria, shut down its western delta operations after attacks and kidnappings, cutting Nigerian oil output by about a fifth.
 
Captives
 
Activists fighting for more control over the region's oil wealth are still holding four oil workers, three Italians and one Lebanese, after an attack on an Agip oil export terminal on December 7.
 
They accused Agip, a unit of the Italian energy giant ENI, of offering ransoms for the workers on Wednesday and vowed to kill the four men rather than free them for cash.
 
A Shell executive said: "We are not sure if this thing is going to deteriorate. If it deteriorates we will have fewer people to contend with."
 
Attacks on oil facilities and kidnappings of workers have become an almost weekly occurrence in the world's eighth largest oil exporter.
 
Rising crime
 
Political violence and crime have risen dramatically this year in the vast wetlands region. The mounting violence is rooted in widespread poverty and decades of neglect by the Nigerian government, which has failed to convert the delta's oil wealth into local jobs or development.
 
Industry executives had been expecting security to decline before a landmark poll next April, because elections often re-ignite long-standing power struggles between rival clans and militias in the remote, lawless region.