This paper presents a model for investigating causes and effects of Cooperative Sourcing in the banking industry. Cooperative Sourcing means merging of similar processes by several firms, such as several banks merge their credit handling operations as well as the underlying IT, to achieve economies of scale. The model is able to capture these factors and to analyze the efficiency of sourcing decisions and resulting market constellations. Due to the complexity of the involved factors, a simulation approach is used for applying the model. Fed with appropriate data the model could support Business Process Sourcing decisions based on analytical analyses as well as on simulation-based compound investigations.