The decarbonization of international shipping has created a clash between WTO norms, such as non-discrimination and market access, and state environmental policies regulating ships, green fuels, and maritime services. Through exploring the ambiguities in technical standards, subsidies, and process-based discrimination, this paper will critically analyze the intersection of WTO law and marine environmental regulation. Through the use of doctrinal legal research and the interpretation of WTO jurisprudence, IMO instruments, and multilateral environmental agreements, this study will assess the scope of the GATT Article XX exceptions. The paper will test the hypothesis that although WTO law has mechanisms for accommodating maritime environmental policy, doctrinal and institutional limitations prevent effective governance, and thus provide ways forward.