The hostage group included an American, two Britons, one Polish man, an Irishman and a Frenchman. They work for a range of oil and construction companies.
An unidentified group of armed men snatched the six workers 10 days ago from a nightclub in the centre Nigeria's oil hub of Port Harcourt.
The kidnappers arrived shooting into the air and sent scores of people rushing for cover. Officials said no one was injured in the incident.
"I appreciate everything everybody's done for us. We're having champagne," said one of the kidnapped men, Royce Parfait, from Tennessee.
Hostage-takings have become almost commonplace in Nigeria where tensions between multinational oil firms and poor local communities have sparked attacks on oil installations.
The hostages are usually taken by groups seeking political concessions or payouts and are rarely harmed.
Sixteen kidnappings in the past two weeks led President Olusegun Obasanjo to declare a crackdown last week.
The government arrested 160 people in the two-day operation, though most of those have since been released.
Lebanese man taken in a different incident was still missing despite earlier reports that all hostages kidnapped in recent weeks had been freed.