sentences:  Bristow opted to discontinue crop-spraying activities in favour of focusing on oil exploration work in Nigeria on behalf of Shell; by the start of the Biafran War in 1967, the company had a fleet of 11 helicopters committed the Nigerian oil exploration effort, based at Port Harcourt.Early on in the conflict, Bristow helped to evacuate oil workers in the region to the safety of Fernando Po; despite the risks, Bristow maintained its Nigerian operations throughout the three years of war via a reduced presence in Lagos and Warri.This decision to remain gave the company a head-start on rivals as oil companies returned to the region after the war's end.