Gunmen kidnapped the man last Friday in the southeastern town of Warri. They killed his driver and demanding a 50 million naira ($310,300) ransom, a security source said.
"The US citizen kidnapped a week ago has been released by his captors," Charles Muka, police spokesman for Delta state, said, identifying him as William Gregory, 50. "We are informed by the company he works for that no ransom was paid."
A spokeswoman in the U.S. embassy said: "I can confirm he was released, but can`t comment further."
The Niger Delta, heartland of Africa`s biggest oil and gas industry, is prone to bouts of unrest and riven by militant factions. Gangs use guns and speedboats to run criminal fiefdoms that profit from kidnapping, robbery and oil theft.
Militant activity decreased after an amnesty for several commanders in 2009, but the region remains volatile.
Gangs in the region usually kidnap for ransoms rather than for political or ideological reasons.
The German Foreign Ministry confirmed on Friday that a German citizen had been kidnapped in northern Nigeria, where a violent Islamist sect is waging an insurgency against President Goodluck Jonathan`s government.
(M014)
Editor: Ella Syafputri
Copyright © ANTARA 2012
