Ollis played for Somerset's second eleven in the Second Eleven Championship and the Minor Counties from 1978, and made his first-class debut in two matches at the end of the 1981 season. He played only once in 1982, but in 1983, he was brought into the team when Somerset's Test players, Ian Botham, Vic Marks, Viv Richards and Joel Garner disappeared on World Cup duty and stayed there for much of the season. Ollis's first game of the season was against Gloucestershire at Bristol; after two declarations, Gloucestershire set Somerset 330 to win in 217 minutes and as opening batsmen Ollis and Somerset captain Peter Roebuck made no attempt to go for the runs. At the designated close of play, they had reached 174 for no wicket, with Ollis not out 99, and Gloucestershire captain David Graveney bowled an extra over in an attempt to secure Ollis his century; however Ollis was unable to score from it, and finished on 99 not out. That proved to be the highest score of Ollis's first-class career, though he passed 50 twice more in the 1983 season on his way to his best aggregate and average, 517 runs at 25.85.