The Italian Ministry of Foreign Affairs in Rome confirmed that four Italian citizens, contracted to Chevron of the US, were abducted.
Sources in the Nigerian state of Bayelsa claim that the other two workers are an American and a Croatian citizen.
A Nigerian soldier was also killed in the rebel attack.
Other details of the attack have not yet been released.
In February, two Croatian citizens, Renato Garma and Mate Lusa were kidnapped in Port Harcourt, Nigeria. The two were released along with Montenegrin citizen, Milan Smolovic, in March.