Leaving school in 1965, Oliver went to work for two years for Sir Peter Scott at the Wildfowl Trust in Slimbridge, Gloucestershire, England. In 1968 Oliver returned to Kenya to take up a position as Game Manager for Ol Pegeta Ranching, responsible for the game management, hunting and control on this 80,000 acre ranch.

Leaving Kenya in 1971, Oliver went to the University of Calgary in Canada and graduated with a B.Sc. in Major Zoology. During vacation time, Oliver returned to Kenya and assisted the Honorary Game Warden on Mount Elgon with elephant, buffalo and lion control.

Oliver returned to Kenya in 1976 and for three years was game manager for Ol Jogi Limited, in charge on anti poaching and game management and control. In 1979, Oliver moved to Naivasha to manage Longonot Farm for Jack and Tubby Block. In 1985, the Blocks sold part of Longonot Farm to Oliver. Oliver and his wife, Jenny, successfully farmed at Lake Naivasha until 2001 when they sold the farm.