Two Croatians and a Montenegrin who were abducted last month in southern Nigeria were released early on Monday, industry sources and diplomats said.
The three men were handed over to security officials in the early hours of the morning, a senior official of a major oil company said.
Their release was confirmed by the Croatian foreign ministry in Zagreb where a spokesman said they were "in good health".
The men who were taken hostage at gunpoint on February 18 in the oil city of Port Harcourt. There was no immediate indication of whether a ransom had been paid.
The three were reportedly abducted as they were out drinking in the city, which has recently become notorious for the kidnapping of foreigners by armed groups.
They were all employed by HydroDive (Nigeria) Ltd, an offshore engineering company that is a subcontractor for Hyundai Heavy Industries Co Nigeria Ltd. They worked on the jobs of supplying the oil platforms in the volatile Niger delta region.
Since January 1 alone, 58 foreigners have been kidnapped by armed gangs and separatist groups in southern Nigeria, almost as many as for the whole of 2006, but most of them have been released.
The kidnappers are a mixture of separatists fighting for a larger share of Nigeria's oil revenue and criminal gangs lured by the prospect of ransom money.
Nigeria is Africa's largest oil producer and derives more than 95 per cent of its foreign exchange earnings from the fossil fuel.