Environmental readiness and registry competition: A comparative assessment of flag States in maritime decarbonization

Flag States occupy a pivotal position in the governance architecture of maritime decarbonization. As primary regulators under the IMO regime, they are responsible for implementing and enforcing environmental standards across globally mobile fleets. Yet flag administrations differ markedly in fleet composition, enforcement capacity, and technological uptake, raising important questions about comparative environmental readiness and institutional competitiveness. This study develops a fleet-level framework to assess environmental readiness across ten major flag States: Cyprus, Greece, Japan, Liberia, Malta, Marshall Islands, Norway, Singapore, Turkey, and the United States. Three dimensions are operationalized using harmonized registry data: decarbonization readiness (alternative-fuel capability), efficiency and modernization readiness (eco/electronic engine technologies), and air-pollution compliance readiness (SOx scrubber installations). A scenario-based multi-criteria decision analysis evaluates how comparative rankings change under alternative policy priorities. Results reveal a layered adaptation structure: efficiency technologies are most widely diffused, scrubbers function as mature compliance tools, and alternative-fuel readiness remains more concentrated. Large open registries achieve stable top rankings under most weighting structures, reflecting broad diffusion across extensive fleets, while registries specializing in advanced decarbonization technologies perform strongly only under transition-focused scenarios. The findings highlight a governance trade-off between fleet scale and the depth of technological transition and demonstrate the importance of scenario-based evaluation in comparative environmental performance assessment.