“The MV Endeavour was off the coast, serving Chevron’s Agbami field, when gunmen boarded it in the very early hours,” Reuters quoted a security source as saying.
Sources said three men may have been kidnapped in the incident which happened off the coast of Bayelsa State.
It is the second attack by armed men on Chevron-contracted vessels off the coast of the state this month.
Chevron said it was investigating the situation but had no further comment.
Experts say recent attacks on ships in the Gulf of Guinea threaten the region’s position as an emerging trade hub that is an increasingly important source of oil, metals and agricultural products such as cocoa for world markets.