Eco-efficiency has been established as a crucial concept for corporate environmental management. Most approaches deal with eco-efficiency on the level of the company or the product. However, given that companies have special budgets earmarked for environmental operations or investments, the question arises as to which operation within which domain is the most eco-efficient. This article presents an approach to supporting these decisions by calculating eco-efficiency on the operational level. The procedure is demonstrated using a case study of the Swiss National Railway Company. Investments and operations in the domains of energy production, landscape and nature conservation, noise protection, and contaminated soil remediation are assessed and compared. Decision-makers seeking an eco-efficient corporate investment policy will find, in this concept, a guideline for prioritizing various domains of operation as well as the operations within a domain.