The tankship 'Aegean Horizon', held by Nigerian port authorities since 13, November 2012, permitted to depart.
The vesel had been held during a regional naval exercise in connection with the alleged theft of some thousands of tons of crude oil.
Aegean Horizon was released on the intervention of Greek President Karolos Papoulias and Greece's Foreign Ministry in Athens, and having left port was heading for Rotterdam.
Reportedly the crew were in normal health.