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In recent years, a strong political ambition to develop ocean energy technologies (OETs) has emerged, especially in Europe. As part of regime shifts towards a decarbonized energy system, the development of OETs is influenced by multi-level interactions occurring between the niche, regime, and landscape levels. This paper deepens the analysis of technological niches (the principal locus for regime change) by analysing the knowledge elements underlying the long-term evolution of OET trajectories. Examination of the relational properties among the knowledge elements in the OET knowledge base allows a better understanding of the structural coherence of the knowledge base within the sector. We use patent data to build a dataset of OET patents granted between 2000 and 2015. Based on this patent analysis, we discuss the knowledge base of OETs and analyse its coherence over time. Finally, we derive policy implications.JEL Codes: O33, Q42, Q55