The allocation of functions and tasks to humans and machines is seldom considered as a step in system design. In those cases where function allocation is considered, it is usually based on fixed schemes for all operators; however, it is possible that the optimal allocation scheme is not the same across individuals. In this research, two studies employed a pasteurizing plant simulation to investigate the effect of gender, age, education, and experience on system performance. Results of the first study revealed individual differences between males and females. However, gender was confounded with education and age. Because this confound could not be removed with the available subject pool, a second study was conducted to separate the effects of age and education on performance. In this latter study, analyses revealed significant individual difference on performance. These data suggest that individual difference variables need to be examined more fully in the system design process.