The increasing short and mid-term demand for oil and gas combined with the fading exploration success brings mature areas back into focus. Especially marginal offshore oil fields, being characterized by high upfront CAPEX, low production revenue and short field life, require innovative solutions, considering specific topics like transfer of CAPEX to OPEX, incentives and technological innovations, which are not necessarily covered in typical upstream valuation approaches. This results in a specific business model that especially considers the value added from adequate subsurface and surface field development competencies and application of fit for purpose technology. Using and adapting the competitive analysis framework of Porter (especially the company value chain and the five forces model) to derive at the pre-dominant value drivers, an adequate valuation concept, taking into account the specifics of marginal offshore oil fields, is configured. Additionally, elaborated expert interviews have been performed to find empirical evidence for derived conclusions.