The men are four Britons, one Romanian, one Malaysian and one Indonesian.
They were kidnapped on October 3 in an unprecedented raid on a residential compound for expatriate contractors working for Exxon Mobil. Two guards were killed by the attackers.
Suur Chafa, the deputy superintendent of police in Akwa Ibom state, where the men were kidnapped, said: "All seven have been released. They are all in good health. They have already been taken to Port Harcourt where the state security services will release them to their various companies."
He did not have any information on the terms of the men's release.
Diplomatic and oil industry sources said a ransom had been demanded and negotiations took place between the kidnappers, the local authorities and the men's employers, four contractor companies based in Britain and the United States.
Romania's foreign ministry confirmed in a statement issued in Bucharest that Romanian oil worker Emil Neagu who was among the hostages had been freed and was in good health.
Paul Arinze, an ExxonMobil spokesman, said Nigerian government officials informed the company Saturday that all the hostages had been released: "We got a notification they have been released and they are all in good health."
Arinze said rumours that one of the hostages had died were false.
Hostage takings for ransom are common in the Niger Delta and local rights activists say companies usually pay up, fuelling the cycle.