Industrial and service sectors offer potential for cost-effective energy savings. Yet underinvestment in energy efficiency is observed in all EU countries. This is called the "energy-efficiency gap". In order to be implemented by companies, energy-efficiency measures have to be analysed and communicated, taking into account the various professional interests and cultures which prevail in a corporate context. Well beyond the mainstream energy saving analysis, a multidisciplinary approach is needed, which requires engineers to be trained in energy efficiency. Classical training for energy engineers focuses on lectures in combination with individual exercises. This training has several shortcomings: exercises usually focus on simple techno-economic assessments; the variety of information sources and interests in a company are improperly represented; strategic concepts, such as competitive advantage or core business, are not included. Therefore, classical training does not develop the skills needed to deal with the multidisciplinary aspects of energy-efficiency measures. It is also well known in pedagogical science that in professional training, the motivation for learning increases when participants can directly apply what they are taught. By providing a virtual training environment, serious games offer the opportunity to manage complex problems and to directly apply any theoretical framework in a fun and collaborative way. This paper introduces a new serious game developed as a training tool for a capacity-building programme on the multiple benefits of energy efficiency. This game puts participants in the context of an industrial company where they play the role of an energy manager who wants to get an energy-efficiency project approved by the Investment Selection Committee. The paper concludes with the preliminary results of training sessions using this serious game.