Outsourcing of urban metabolisms is a phenomenon that has grown exponentially over the last century. It is a cause of vulnerability for cities for two main reasons. They are dependent on distant hinterlands and their consumption induces global environmental impact they do not fully control. This study aims to investigate these two effects of outsourcing through a single, multiscale approach to energy accounting. A spatially differentiated energy flow analysis (EFA) is developed, which includes indicators for dependency, embodied energy and energy losses. Applied to the case of the harbor-industrial area of Saint-Nazaire, France, the results show that the global scale dominates dependency and embodied energy indicators, whereas primary energy losses occur mainly at the domestic scale. The local scale accounts for less than 0.1% of the energy supply and about 6% of indirect flows. The spatial trajectories of some renewables (wood, biofuels, wind electricity) suggest that the energy transition could decrease global dependency, but with a transfer to the domestic level, and not necessarily to the local scale, without a radical change from the port's production system. Moreover, trade-offs could emerge between reducing the amount of embodied energy in foreign countries and using energy losses as a local secondary source, depending on the resource used to generate the losses. This study highlights thus the need to link local transition policies more closely to outsourcing issues in order to allow a comprehensive understanding of the possible transfers in terms of dependency and environmental burdens that may occur in a transition context.