sentences:  Throughout much of 1970s, Nigeria functioned as Bristow's biggest profit center; it continued to grow through the decade via contracts from Shell, Mobil, Texaco and other companies.In the mid-1960s, Bristow opted to enter the North Sea market; being the second helicopter operator (after BEA Helicopters Limited) to establish operations at Aberdeen, Scotland, it was relatively well positioned to take advantage of the region's oil boom.Starting on 17 February 1965, the company operated the Westland Wessex 60 ten-seat helicopter to support these off-shore installations.