In theory, the energy that could be extracted from ocean waves is in excess of any current, or future, human requirements. Methods to evaluate and compare the wave energy resource at different locations are required in order to inform the developers of Wave Energy Converter (WEC) projects and allow them to select the most favorable sites for achieving optimal power capture and economic performance from their devices as the wave energy industry begins to approach the commercial deployment of Wave Farms, arrays of full-scale WECs. In this paper alternative techniques for the characterization of wave energy resource are presented, with particular emphasis on the identification of the practicable power available for extraction and the comparison between different potential locations for Wave Farm developments. The effect of introducing a threshold, beyond which the theoretical wave power is no longer deemed exploitable and ignored for the purposes of resource evaluation, is highlighted in order to account for the reduced device output that can be expected in severe storm conditions. In addition, the relative performance that could be expected of typical WECs located at different sites is determined using the power matrices made publicly available by the a number of device developers. These methods are applied to measured buoy data to allow for the comparison of the wave energy resource at the Atlantic Marine Energy Test Site, a grid connected location for the testing of full scale WECs being developed near Belmullet, County Mayo, by the Sustainable Energy Authority of Ireland (SEAI), with the incident wave conditions experienced at locations on the Pacific and Atlantic Coasts of the United States. Instances where sea states with the same summary statistics display radically different spectral shapes have been identified, consequently the level of variation in the dominant spectral shapes that can exist between two ocean sites is also investigated. The effect that this spectral variation can have on the characterization of the wave energy resource at different sites and on the performance of WECs is demonstrated and discussed. It is shown that the sea states which are responsible for the largest contributions of wave power, as opposed to the most commonly occurring conditions, which should be deemed most significant for the deployment and operation of WEC installations.