Marine engine emission regulations include:

EPA - The United States Environmental Protection Agency (EPA) regulates exhaust emissions from diesel engines installed on U.S. flagged / registered marine vessels. Engines ≥ 600kW (805hp) must be EPA Tier 4, while engines with lower power are EPA Tier 3.

EU - The Nonroad Mobile Machinery Directive regulates exhaust emissions from marine propulsion and auxiliary engines used on inland waterway vessels operating in the European Union. These engines must be certified to EU Stage V. The Recreational Craft Directive (RCD) regulates exhaust emissions from propulsion engines used on recreational craft. These engines must be certified to RCD2.

IMO - The International Maritime Organization (IMO) regulates exhaust emissions on diesel engines above 130 kW (174hp); engines used exclusively in emergency applications are exempt. Currently at IMO Tier II, however IMO Tier III applies for certain vessels when operating within a NOx Emission Control Area. These include the North American ECA and U.S. Caribbean Sea ECA (effective Jan 1, 2016), and the North Sea ECA and Baltic Sea ECA (effective Jan 1, 2021).

China – The China Ministry of Ecology and Environment (MEE) regulates exhaust emissions from diesel engines on China flagged / registered marine vessels operating inland and/or coastal. Marine engines are currently at China Stage II emissions level.