MARPOL Annex VI

SOx — sulphur cap

Global sulphur cap of 0.50% m/m entered force 1 January 2020 (IMO 2020). Reduced to 0.10% m/m in the four Emission Control Areas (SECAs): Baltic, North Sea, North American, and US Caribbean. Compliance options: (a) burn compliant low-sulphur fuel; (b) use exhaust gas cleaning system (scrubber); (c) alternative fuel (LNG, methanol, ammonia, biofuel). Charterer + PSC focus on Bunker Delivery Note retention (3 years), fuel-sample retention (until vessel next fuels or 12 months), and Fuel Oil Non-Availability Report (FONAR) when compliant fuel unavailable at a bunker port.

NOx — Tier I/II/III

Nitrogen oxide emissions tiered by keel-laying date:

• Tier I — keels laid 1 Jan 2000 to 31 Dec 2010; global cap 17.0 g/kWh (at 130 rpm engine speed).
• Tier II — keels laid 1 Jan 2011 onward; global cap 14.4 g/kWh.
• Tier III — keels laid on/after 1 Jan 2016 operating in ECA-NOx zones; cap 3.4 g/kWh. Requires Selective Catalytic Reduction (SCR) or Exhaust Gas Recirculation (EGR) system.

Tier III applies only in the North American + US Caribbean ECAs currently; the Baltic + North Sea ECA-NOx zones apply Tier III for ships built after 1 January 2021.

EEXI — Energy Efficiency Existing Ship Index

EEXI entered force 1 November 2022 with first compliance at 2023 IAPP renewal. Every existing vessel >400 GT calculates an EEXI value against a reference line specific to ship type + size. Non-compliant vessels must implement power limitation (usually via Engine Power Limitation, EPL, or Shaft Power Limitation, SPL) to reduce theoretical maximum output. The EEXI Technical File — signed off by Recognised Organisation — is now part of the ship's statutory certification portfolio.

CII — Carbon Intensity Indicator

Operational carbon intensity rating (A/B/C/D/E scale) — the annual report card. Calculated from IMO DCS (Data Collection System) fuel-consumption data + distance travelled. Ships receiving three consecutive D ratings or a single E rating must submit a Corrective Action Plan (CAP) with the SEEMP Part III. See our CII rating calculator.

GHG Strategy — the 2050 net-zero pathway

The 2023 IMO GHG Strategy (Resolution MEPC.377(80)) commits to net-zero GHG emissions by or around 2050, with indicative checkpoints of 20% reduction (striving for 30%) by 2030 and 70% reduction (striving for 80%) by 2040, both compared to 2008. MEPC 83 (April 2025) adopted the mid-term measures: the Global Fuel Standard (WtW GHG intensity requirement) + the economic measure (bunker levy on emissions above a threshold), entering force 2027. Also see our EU ETS + FuelEU Maritime page for the EU-specific framework.