Abel Oshevire, a Nigerian official, said that Cody Oswald and Russell Spell, both Americans, and John Hudspith, a Briton, had been handed over to officials after being held captive in the swamps of the Niger Delta.
"They're all here. They're all OK," the Delta State spokesman said.
The three men were among a group of nine foreign workers who were kidnapped on February 18 by armed militants fighting for control of the delta's oil resources.
The other six men were released after a week.
The men, who work for the US engineering firm Willbros under contract to the Anglo-Dutch energy giant Shell, had been working on a pipe-laying barge on a river opposite a large oil export terminal when they were captured.
Militants from the Movement for the Emancipation of the Niger Delta exchanged fire with navy troops during the kidnapping.
They had demanded that Shell pay $1.5 billion in damages to polluted Ijaw communities and that the government release two prominent regional leaders from jail.
After the kidnapping the group also stepped up dynamite attacks on oil pipelines and wells, hitting facilities operated by Shell, the American company Chevron and the Italian company Agip, a subsidiary of ENI.
Nigeria is Africa's biggest oil producer and exports about 2.5 million barrel per day.