Modern refineries are complex, very high in value and production. They are expected to function for years to come, with ability to handle the change in technology and feed quality. The aging of a refinery and continues increase of vendors and contractors numbers forces the refinery's operation management to design a support system which can capture these changes. Furthermore, an accurate performance measurement and risk evaluation processes are highly needed. Therefore, this paper explores the nature of the support system design for a refinery. The research work explores the operation support system from a range of perspectives, interviewing managers from across the refinery organization. The factors contributing to complexity of a support system are described in context is presented which clusters them into several key areas. It is proposed that this framework may then be used as a tool for analysis and management of support system. The paper will conclude with discussion of potential application of the framework and opportunities for future work.