Total Site Analysis (TSA) is a tool for quantifying energy savings targets in large industrial process clusters. Thereafter retrofit design tools can be used to identify efficient solutions in which the different process sites exchange excess energy with each other through the site utility system, thus reducing the overall need for external fuels/energy. Compared to energy efficiency investments identified for single companies, similar investments identified for clusters hold an inherent complexity; they assume joint investments and multi-party collaboration, which often constitute a barrier for implementation. Real Options Analysis (ROA) is a tool that can be used for helping managers to evaluate different investment options. However, previous research almost exclusively concerns single companies/actors and not the increased complexity of joint investments. This paper presents a novel approach, showing how ROA can be applied not only to handle uncertainties regarding market development but also reduce complexity associated with multiparty cooperation in a joint energy efficiency investments based on TSA. The approachis applied on a case study of a joint energy efficiency retrofit investment in a Swedish chemical cluster. Using ROA, the case study shows how the identified solution can divided into “investment packages” distributed over time, allowing for an initial investment by only two actors and permitting for an evaluation of both the cooperation and the market development before expanding the investment and the number of actors involved. Further, an economic assessment of the project is presented together with an analysis of the cost/ benefit of gradually expanding the investment.