A container terminal can be defined as a mass service system in which a multiphase service processes takes place. The terminal consists of three subsystems: quayside, yard and gate. In this paper, queuing theory as one of the operational research method is been used, to determine indicators of functioning the service system on the example of the container terminal of the port of Rijeka. Applying the queueing theory, the service phases that represent a bottleneck can be determined, as well as the phases in which the largest capacity surpluses are located. Finally, based on the current capacities the optimal turnover of the terminal was provided, without congestions and with the highest degree of terminal utilization. The basic conclusion is that the capacity of the system is limited by the capacity of the subsystem that has the smallest capacity, and in this case it is gate/truck and train operation area.