This paper develops a decision rule to enable an a priori classification of a production system that should utilize a JIT- or WIP-type inventory control policy. A two-station deterministic serial production system is analysed. A parameter a— the ratio between WIP and maximum shortage—is defined, and a cost function K — f( α) is modelled. It is shown that α*—an optimum value of α—is a characteristic parameter of the system, can be evaluated a priori based on known parameters, and can serve to identify a production system as JIT type or WIP type. The concept of an OC curve of a system is introduced and it is concluded that JIT is not always favourable over WIP.