 John Bracewell, Gloucestershire's coach, viewed O'Brien as primarily a one-day player and believed his style of batting was best suited to situations where the team needed to increase their run-rate.He made his debut for Gloucestershire on 15 May, scoring three runs from four balls in a CB40 match against Glamorgan.In June he scored his first century in twenty20 cricket, beating his previous highest score of 39.