Abstract The aim of this paper is to describe a method to integrate the results of process simulations in availability studies. It is shown that this can be achieved if two conditions are met: firstly, close co-operation between process experts and reliability engineers and secondly, a flexible modelling tool. Principles of the modelling method, the interpreted stochastic Petri nets, are provided. The way to use them to model plant availability is described, together with a computer code enabling calculations to be made. The aim of the plant availability study and how results of process simulations were integrated in the Petri net model is then explained. Results are discussed and conclusions given on the ability of interpreted stochastic Petri nets to model complex systems.