Twenty Eastern European sailors have been captured by pirates who seized an oil tanker off the coast of Nigeria, the vessel's owner said Wednesday.

The MT Cape Bird, hijacked about 90 nautical miles from Lagos on Saturday night, is still drifting there with the sailors and pirates onboard, said a spokesman for the United Product Tankers GmbH & Co. KG in Hamburg, Germany.

The spokesman could not comment on whether or not contact had been established with the vessel and did not know the nationalities of the sailors. He spoke on condition of anonymity in line with company policy.

The Nigerian Navy has said it received reports that the vessel was carrying either crude oil or refined gasoline. The United Product Tankers spokesman said the cargo was an oil product, but that he did not think it was crude.

Nigerian Navy vessels have orders to stop the tanker if they find it and to arrest the hijackers.

Analysts expect the ship and its crew to be released within the next few days.

"We know that in some of the cases, they get a ransom, but that is a small amount compared to the main target," said Hans Tino Hansen, CEO of the Denmark-based security firm Risk Intelligence. "The main target is either to use the ship to transfer oil or to steal the crude or refined oil that is on board."

Hijacked ships off the West African coast are usually released after about ten days, he said.

The hijacking is the latest to target West Africa's Gulf of Guinea, which follows the continent's southward curve from Liberia to Gabon. Over the last eight months, piracy in the oil-rich region has escalated from low-level armed robberies to hijackings and cargo thefts, according to Risk Intelligence.

In August, London-based Lloyd's Market Association, an umbrella group of insurers, listed Nigeria, neighboring Benin and nearby waters in the same risk category as Somalia, where two decades of war and anarchy have allowed piracy to flourish. However, some analysts say Somali-style piracy is much different to the kind now growing in West African waters.

Risk Intelligence research suggests that that Somali pirates keep hostages for six to eight months and walk away with ransoms averaging $5 million dollars.

"In Nigerian hijackings, they may get a value of crude or refined oil worth twice or four times as much, and they get it in a week," Hansen said.