In this paper, the effect of discrete batch transfer of WIP between workstations on the efficiency of asynchronous production lines is analysed via a simulation model. The processing times are assumed to be random variables distributed according to specific distribution functions. The WIP transfer design problem involves determining the number of containers to allocate to each buffer location and the container capacity. Interesting and valuable information for practitioners has been obtained. It is found that loss in capacity occurs in the first few stations. Another finding is that an important portion of the lost capacity can be regained by allocating two containers to each buffer location, and if it is impossible to assign two containers to each location, then no single-container location should be adjacent to another single-container location.