Examines the relationship between operator characteristics and process control performance in high-risk process industries. 39 trainee operators (aged 16-22 years) at different Swiss chemical companies participated in a 4-hour training session of a simulated process control task and a testing session in which various system faults had to be managed. Cognitive ability (Wonderlic Personnel Test), cognitive flexibility (Cognitive Flexibility Inventory), self-efficacy and personality traits were measured as operator characteristics. Cognitive ability related positively to system control performance but not to diagnostic performance. Participants with low cognitive flexibility performed best on system control, whereas participants with high cognitive flexibility performed best on diagnostic performance. A hierarchical regression analysis revealed that cognitive ability, cognitive flexibility, and declarative knowledge accounted for about 30% of the variability of system control. It is recommended that the consideration of cognitive ability and cognitive flexibility be increased in personnel selection for complex work environments.