Organizations engaging in electronic commerce typically are faced with defining detailed bilateral agreements between business partners. This implies that set-up costs for new electronic linkages can be quite high. There is a growing need to model and simulate this form of interorganizational interaction to lower these costs. The research presented contributes to this problem in two ways by: stipulating requirements on representation languages to be used for modelling trade procedures; and presenting a common graph-based representation language, Documentary Petri Nets, which satisfies these requirements. The practical implementation of Documentary Petri Net models is illustrated using a modelling environment, Case/Open-edi, a tool that may be used for the design and analysis of trade procedures. A simplified documentary credit procedure is used to give an example of such a Documentary Petri Net model. Finally, conclusions and directions for research are given.