Seven expatriate oil workers abducted on October 3 in the restive Niger Delta region of Nigeria were freed on Saturday in the district capital Port Harcourt, police and oil company sources said.
Police spokesman Hza Iwendi gave no details of their release but said the four Britons, a Romanian, a Malaysian and an Indonesian, would be transferred to the care of their employers -- subcontractors for US oil giant Exxon Mobil.
"It's very good news and we are really very happy," a spokesman for Exxon Mobil told AFP, confirming their release.
In London, Foreign Office minister Lord David Triesman said: "I am pleased at the successful outcome to this kidnap and would like to express our thanks to the Nigerian authorities for all their help and assistance."
No details were available about the circumstances surrounding the release, nor about their health.
The employees of Sparrow Offshore and Oceaneering International were kidnapped on October 3 by unknown armed men who attacked an installation of the company in Eket, a major town in south-eastern Akwa Ibom State.
Two Nigerian employees were believed to have been killed during the attack for which nobody claimed responsibility.
The kidnappings were the latest in a series of incidents in recent months that have slashed oil output of 2.6 million barrels per day in Nigeria -- the world's sixth largest producer -- by a quarter.
Around 10 days ago, about 60 Nigerian employees from Anglo-Dutch oil group Shell and subcontractor firms were captured in the southern state of Bayelsa before being freed two days later.
The week before that another Shell plant was attacked in neighbouring Rivers State by around 70 heavily armed men. Fourteen soldiers were killed and 25 workers were seized before being kidnapped over the following two days.
Shell, which produces around half of Nigerian oil exports, is currently losing around 477,000 barrels per day in output due to the unrest.
Local groups carrying out the kidnappings, such as the Movement for the Emancipation of the Niger Delta (MEND), are angry at the environmental degradation caused by the oil wells and that the proceeds have not filtered down to the local population, who live in dire poverty.
According to the United Nations Development Programme (UNDP) the majority of the region's population live on less than a dollar a day. Oil exports account for around 95 percent of Nigeria's foreign currency receipts.
The lure of petrodollars has also attracted criminal gangs seeking to extract ransoms for kidnapped foreign workers. Nigeria is also rife with corruption, with a recent report estimating that past leaders have stolen about 50 trillion naira (385 billion dollars, 310 billion euros) since independence in 1960.
Nigerian President Olusegun Obasanjo has visited the Niger Delta region twice this month and two weeks ago called a crisis meeting with top security officials.
It was unclear if Saturday's hostage release followed a ransom payment, with a Nigerian arraigned on Tuesday for allegedly demanding a ransom of 90 million naira for the release of the seven expatriates.