The reliability of wave energy converters (WECs) is a key issue that has to be addressed in order to make them a viable energy option. At this stage of early industrial development the reliability assessment of WECs is a challenging task. In this paper existing reliability methods, namely Reliability Block diagrams, have been applied to a notional configuration. It was found that omnipresent lack of failure rate data makes rather crude adjustments of often generic data necessary which generally lead to rather unfavourable and highly uncertain results. Reliability data is either not available due to sparse field experience or is kept confidential, within different project developments to secure competitive advantages and intellectual property. In order to foster the progress of the marine energy industry, the reliability of devices must be demonstrated and improved. This requires a joint effort between industry stakeholders to collect, share and disseminate existing failure knowledge and future operational experience