Cross-organizational requirements engineering (XRE) is the activity in which several business actors perform a joint problem-solving process in which a cooperative, cross-organizational business solution is designed. In XRE, partially conflicting concerns and views must be reconciled to create a shared vision of the goals and structure of a cooperative process. In this paper we report on the development of an XRE method, BusMod, by means of action research. Each iteration of our action research cycle consisted of a series of consultancy projects in which our method is used, followed by a reflection to draw lessons learned to improve the method. Although BusMod has been developed in the domain of electricity power generation, we hypothesize that it can be generalized to any domain of cooperating actors, and that in any such domain value engineering must be part of requirements engineering.