German Hostage Free

"He was released at 11pm. No ransom was paid," a source at the hostage's employers, Julius Berger, told Reuters news agency.

Details of the abduction remain sketchy, but unknown gunmen killed at least one military escort during the kidnapping near Emuoha in the Niger Delta. And there are conflicting reports about the fate of the foreign worker's driver.

The German-Nigerian construction company Julius Berger is currently upgrading the road there, which leads out of Port Harcourt, the area's main city.

Is the threat to foreign workers growing again?

The unnamed German was the first foreigner seized since October in the Delta. It is unclear whether Tuesday's abduction was an isolated incident or signals a return to more unsettled times for expatriates.

Over 200 foreign workers have been kidnapped by militants and ransom seekers since 2006. Nearly all of them were released unharmed.

The record oil prices on world markets has, in part, been triggered by the violence and supply disruptions in the Niger Delta, the base of Africa's biggest oil industry which produces 2.1 million barrels per day.

Extremes of wealth and poverty exist side-by-side

Social tensions are great in the Niger Delta where the poverty of the local community stands in start contrast to an industry, run by multinational companies, that earns billions of dollars annually.

Armed groups campaigning for greater local control over oil revenues and compensation for air, land and water pollution have blown up oil production facilities and kidnapped foreign oil workers to push through their demands.

But kidnapping is also big business in the area, and it is not just restricted to foreign workers. Abductions of Nigerians judged wealthy enough to pay a ransom, have not undergone a lull since October, but have continued unabated.