The GRACE project aims at supporting policy makers developing sustainable transport systems by facilitating the implementation of pricing and taxation schemes that reflect the costs of infrastructure use. This deliverable D4 falls within GRACE workpackage 2: case study research on marginal social costs in ports, maritime shipping, airports and inland navigation. Case studies address infrastructure, congestion and environmental costs. The aim of this deliverable was to carry out case study research to address gaps in the existing levels of knowledge of marginal social costs for air and waterborne transport. Four components of marginal costs were distinguished in this deliverable: - Infrastructure costs (refer to costs for replacement, maintenance, operation and control of transport facilities); - Transport user costs (refer to users of transport facilities); - Supplier/operating costs (refer to providers of transport facilities); - External costs, (refer in this deliverable to accidents, pollution and noise). The short-run marginal cost is the appropriate base for pricing, irrespective of having under- or overcapacity. The aim of pricing is to confront the user with the additional costs that he/she causes. Only the short-run marginal cost indicates precisely the difference in costs between acceptance and refusal of an additional user. The (un-)availability of data has led to several approaches of the case studies. The port case study is based on an engineering approach. The inland navigation case study starts from a cost-allocation approach and the air case study from an econometric approach.