This work aims to determine the exploitable wave energy resource at five potential sites close to harbour protection facilities at the Portuguese coast, namely at the Azores archipelago, at Madeira Island and at Sines, on the coast of mainland Portugal. For that purpose, a third-generation wave model SWAN is used to transfer the offshore estimates of sea wave conditions to those points over the last 40 years. Sea states and wind fields are provided by the climate reanalysis datasets ERA5. Using sea states as boundary conditions and wind fields as forcings in the numerical domains of the SWAN model, the sea states were propagated shoreward, in order to estimate and analyse the wave conditions in the regions of interest. By combining the average energy flux per unit length of wave front and the probability of occurrence of each sea state, the average exploitable annual energy per unit length of wave crest can be computed. The variability of this energy flux is analysed since it is of paramount importance for the efficiency of Wave Energy Converters (WEC). This assessment showed that the best location for the installation of dual-chamber OWC devices is at the Azores archipelago.