‘ Bowl phenomenon ’ refers to the increase in production rate obtained by unbalancing a series production system such that the service time increases progressively on either side of the central stage(s). While such a result is valid for production systems with otherwise identical stages, earlier studies have suggested that a different effect may come into play when the stages of the system differ in their variability. In the simplest case of n two-stage system, production rate could be improved by shifting a part of the work load from the more variable stage to the less variable one.