The five, whose nationalities are unknown, were seized by armed men who attacked an oil installation at Eket, in the southern state of Akwa Ibom.
The source also said two Nigerian employees of Exxon were killed.
The assailants were not immediately identified and there was no immediate claim of responsibility.
But the Niger Delta, home to Nigeria’s multi –billion dollar oil and gas industry, has seen a resurgence of violence by separatist militants seeking local control of the country's oil resources.
Attacks on oil installations in the region have cut about a quarter of oil production since the start of the year and at least five Nigerian staff employed in the oil sector have been killed by unknown attackers.
On Monday, about 70 men attacked a site belonging to the Royal Dutch Shell company in Rivers State. Military and company sources said 14 soldiers were killed and 25 workers were kidnapped.
Nine of those workers were freed on Tuesday, and authorities in the state were negotiating with the kidnappers to obtain the release of the 16 others.
Responsibility for that attack was claimed by the Joint Revolutionary Council (JRC), a group of several separatist movements.
The JRC said in a statement published by several dailies that the attack was aimed at obtaining the immediate release of Alhaji Mujahid Dokubo Asari, the imprisoned leader of the Niger Delta People's Volunteer Force (NDPVF).
In October 2005 Asari was charged in an Abuja Federal High Court with treason, illegal assembly and conspiracy.