Fifteen Eastern European sailors have been sentenced to six months in prison after admitting to stealing 11,300 tonnes of Nigerian crude oil.
The men were freed on bail in September
Judges immediately freed the men, who had already spent two years in custody in Nigeria.
They were arrested aboard the Greek-owned tanker African Pride by security forces in October 2003 and charged with stealing the oil.
The ship and its cargo later vanished from the custody of the Nigerian navy.
Two rear admirals were court-martialled for their involvement in the disappearance.
The ship has not been recovered, though Nigerian media have reported a sighting in the Middle East.
Judge Gloria Okeke was quoted by the Associated Press news agency as saying the 15 men had pleaded guilty to reduced charges of illegal oil possession.
They were initially charged with oil-smuggling and economic sabotage, which would have led to much longer prison sentences if they had been convicted.
In September, the sailors were released on bail after diplomatic missions guaranteed they would show for their trial.
"I can't believe I'm free," ship engineer Ivan Martemyanov said as he received his seized passport from court officials. "Being in prison was the worst time in my life."
Nigeria, the world's eighth-biggest oil exporter, is estimated to lose between 100,000 and 250,000 barrels daily to oil thieves.