Today, enterprises have to cooperate to survive in an increasingly competitive environment. This cooperation is carried out using networked organisations. To cooperate in the best way possible, each enterprise must be interoperable with many other ones. From an engineering point of view, it is necessary to model the enterprises and their collaboration, to detect where interoperability is considered less than expected, to evaluate the effort necessary to fill the lack of interoperability and to propose solutions to improve the situation. This paper focuses on the modelling, detection of non-interoperability and evaluation of efforts issues. First, this paper exposes the problems of interoperability, focusing on organisational interoperability and the necessity of using enterprise modelling techniques. The second part of this paper is dedicated to the presentation of a method enabling the characterisation of organisational interoperability and the evaluation of effort needed to reach or maintain the targeted interoperability level. This method is based on enterprise modelling, graph theory and rules checking. The third part of the paper presents in detail the five main rules of the method. This presentation is proposed through a real case study to demonstrate its applicability. A discussion of the research results is presented at the end of parts two and three. Finally, a conclusion and some perspectives are presented at the end of this paper.< Réduire