Nigerian security forces have located a vessel hijacked by armed militants, a security official said on Monday.
"We have located the vessel and we are drawing up our strategy to free the hostages, all its 11-man crew," the official told AFP on condition of anonymity.
The attack on the Chevron vessel, Lourdes Tide, took place late Tuesday between Onne, near the oil city of Port Harcourt, and Escravos in southern Nigeria.
The hostages number nine Nigerians, a Portuguese and a Ukrainian.
An initial plan by security forces to storm the vessel was dropped on the advice of the American oil giant, the official said.
The source did not say if forces were in contact with the gang that abducted the men when they intercepted the boat carrying supplies for Chevron.
No group has claimed responsibility for the attack.
Military Joint Task Force spokesman Lieutenant Colonel Musa Sagir had earlier told AFP that the attackers had asked for a ransom of 30 million naira (260,000 dollars or 165,000 euros) for the hostages' release.
Chevron confirmed the attack and promised to assist in the release of the hostages.
In 2007 alone, more than 200 foreign workers were taken hostage, often being released after a ransom was paid.
Most of the attacks and kidnappings have been claimed by the Movement for the Emancipation of Niger Delta (MEND), which is the most prominent militant group in the restive region.
The attacks by militant gangs have reduced Nigeria's total oil production by a quarter in the past two years.
Nigeria, still Africa's largest oil producer with a daily total production of 2.1 million barrels, derives about 95 percent of its foreign earnings from the sector.