Four foreign oil and gas contractors kidnapped off the coast of Nigeria's volatile oil-rich southern delta have been freed, their company said Thursday.

The four men were in good health when officials recovered them Wednesday night from the Niger Delta region, said spokeswoman Corrie van Kessel of the Sea Trucks Group, an oil and gas contractor with offices in Rotterdam, the Netherlands. She said the men received medical checkups after their release and were safe.

"It looks as if it's all OK," van Kessel said. "We've informed their families and the local consulates."

Nigeria's navy had said those abducted by the gunmen included an Indonesian, an Iranian, a Malaysian and a worker from Thailand, though van Kessel had declined to offer their nationalities after the Aug. 4 kidnapping. It also was unclear how the men were released. Van Kessel declined to say whether a ransom had been paid for their freedom. While kidnappings in the delta routinely involve violence, most hostages are released a few weeks later unharmed after their employers pay a ransom.

The attack Aug. 4 happened about 35 nautical miles off the coast of the Niger Delta, a region once beset by militant and criminal attacks and kidnappings that has seen relative calm since a government-sponsored amnesty deal a few years ago. The gunmen opened fire on the sailors, killing two and wounding two others in the attack, the Nigerian navy said at the time.

Foreign oil companies have pumped oil out of the delta for more than 50 years. Despite the billions of dollars flowing into Nigeria's government, many in the delta remain desperately poor, living in polluted waters without access to proper medical care, education or work. That sparked an uprising by militants and criminals in 2006 who blew up oil pipelines and kidnapped foreign workers.

That violence ebbed in 2009 with a government-sponsored amnesty program promising ex-fighters monthly payments and job training. Few in the delta, however, have seen the promised benefits and scattered kidnappings and attacks continue. Theft of crude oil from pumping stations and pipelines also has risen drastically recently in the winding creeks of the delta, a region about the size of Portugal that remains difficult for the military and police to patrol.

The last major kidnapping of foreigners in the delta happened in November, when gunmen attacked a ship supplying a Chevron Corp. offshore oil field, kidnapping three workers. The three later were released in December.