An oil supply vessel and tugboat were ambushed off the coast of the Niger Delta region in Nigeria in two separate incidents on Friday.
It was the latest in a series of attacks - 10 have been reported so far this year.
Ten armed men in two speedboats early on Friday attacked the MV Ngoni, an oil supply vessel working under contract by Exxon Mobil.
In a separate incident, 20 gunmen in three speedboats hijacked a tugboat near the same area.
No one was reported to be hurt and the tugboat was later recovered.
According to the International Maritime Bureauthere were 40 reported incidents of piracy in Nigeria last year - including 27 vessels boarded, five hijackings and 39 crew members kidnapped.