AbstractPerformance modeling and analysis of a computation is at the heart of the parallel/distributed processing area. Past research efforts produced the computation structure model that can be used to describe the performance behavior of parallel/distributed software at the computation level. How-ever, the model was used only for shared-memory computations. In this paper, we investigate how the model can be used for computations that use rendezvous message-passing communication. Occam is used as the underlying language to implement the computations. A software tool OCAS (Occam Cost Analysis System) is constructed based on the de-veloped techniques to derive the time cost of a given Occam program.