Another nine crew members were safe and had reached the Nigerian port of Onne, in the oil-rich Niger Delta, said the spokeswoman for Bourbon, which supplies vessels to the offshore oil industry. The seven were abducted on Monday.
Pirate attacks are on the rise in the Gulf of Guinea, which is second only to the waters around Somalia for piracy.Usually boats are attacked in order to steal their cargo, after which the crew is normally freed, although kidnapping is also a major criminal enterprise in the waters around the delta, the heart of Africa’s biggest energy industry.
Pirates freed a Greek-operated gasoline tanker earlier this month that they had hijacked in the Gulf of Guinea near Ivory Coast. Fuel ships are a favourite target.
Many of the criminal gangs in pirate networks are offshoots from militant groups that used to operate in the delta before they agreed an amnesty in 2009.
In August pirates attacked a Greek-operated oil tanker with a crew of about 20 off the coast of Togo. They released the ship a few days later after stealing 3,000 tonnes of fuel.
The African Insurance Organization (AIO) recently designated Nigeria as global capital for kidnap for ransom due to the huge record of kidnap cases reported in the country yearly. Nigeria accounted for a quarter of globally reported cases in the first quarter of 2011.