Knowledge of maritime traffic and knowledge of the behaviour of this traffic is essential for a successful maritime risk assessment study. For many years such knowledge has been built up and improved within Dutch national projects for the Maritime Safety Agency (DGSM) and North Sea Directorate, both part of the Ministry of Transport, Public Works and Water Management, and within European projects, COST 301 and EURET, for the European Commission. Based on this knowledge the MANS-model (Management Analysis North Sea) was developed, a toolbox with models to facilitate the comparison and evaluation of policy alternatives with respect to the use, physical planning and management of the North Sea. One of these models is the Ship-Offshore platform Collision Risk Assessment (SOCRA) model. This model is described in more detail in this paper.