Risk premiums for kidnap for ransom insurance or terrorism insurance will be reviewed across the north Africa region in light of the attacks, says Mr Robson.

CNN: Oil and gas industry reviews security

Malaysia's Sabah state shares a sea border with the southern Philippines, which is home to a number of Islamic militant and kidnap-for ransom groups.

BBC: Malaysia stand-off with Philippine group

Local activists in the Niger Delta, which produces most of Nigeria's oil, regularly kidnap oil workers for ransom or smash installations, sometimes seriously cutting production.

ECONOMIST: Nigeria

Others suggest that Mr Reinhart did not have kidnap insurance, and so might have been personally liable for his employee's ransom.

ECONOMIST: Guerrilla tactics