Typically, most research on job shops has been conducted only on balanced job shops. This implies that there is no work center that regulates the processing speed of other work centers. However, in practice, in most cases, job shops are unbalanced. There exist bottleneck work centers that delay the flow of other work centers, and these bottleneck work centers have a significant impact on shop performance. Despite the importance of bottleneck work centers, research on this topic has been extremely limited. Therefore, this paper first develops a job shop model with a bottleneck work center, and then analyzes and investigates the effects of the existence of a bottleneck work center on various performance measures of the shop within this model. This investigation is conducted using a simulation model.