China enters a new era of green shipping with its commencement of the enforcement of the Domestic Emission Control Area (DECA) regulation at its major port regions.  This regulation limits the sulfur level of fuel used on ships in and near the port areas at 0.5 per cent, 86 per cent lower than the 3.5 per cent global marine fuel sulfur standard.  The real benefits of the DECA regulation will depend largely on how well it will be enforced.  Establishing a robust enforcement program for DECA is particularly important because DECA is the first marine fuel regulation to have been enacted in China.  In order to help the Chinese government effectively enforce this regulation, the Natural Resources Defense Council (NRDC) has developed this report to review and summarize key elements of programs adopted in the US, Europe, and Hong Kong in order to verify compliance with marine fuel regulations and deter violations.  The report also discusses strengths and limitations of the different enforcement approaches and technologies. Drawing from the lessons learned from the current enforcement programs adopted in other regions, the report offers recommendations for China to consider in enhancing its DECA enforcement program.