Part of MARPOL Annex VI, entered into force in 1997, revised in 2015.

Progressive reductions in NOx emissions from marine diesel engines installed on ships, with a “Tier II” emission limit for engines installed on a ship constructed on or after 1 January 2011; and a more stringent “Tier III” emission limit for engines installed on a ship constructed on or after 1 January 2016 operating in ECAs.

NOx and PM ECAs are the North Sea, the Baltic Sea, the coasts of the United States and the Atlantic and Pacific coasts of Canada.
SOx ECAs are the Baltic Sea, the North Sea and the coasts of the United States and the Atlantic and Pacific coasts of Canada.

In 2015, the limits for SOx and particulate matter (PM) were reduced to 0.1%.

– Source: International Maritime Organization –

Part of MARPOL Annex VI, entered into force 2020.

The global fuel oil sulphur limit was reduced from 3.5% to 0.5%.

– Source: International Maritime Organization –

Part of MARPOL Annex VI, entered into force 2013.

The EEDI is a non-prescriptive, performance-based mechanism that leaves the choice of technologies to use in a specific ship design to the industry. As long as the required energy efficiency level is attained, ship designers and builders are free to use the most cost-efficient solutions for the ship to comply with the regulations.

EEDI is the IMO’s principle technical measure to reduce GHG emissions. EEDI applies to any ship of 400 gross tonnage and above that are engaged in international waters. Requires calculation of Attained EEDI (Regulation 20) and Required EEDI (Regulation 21).

The formula for Attained EEDI (the actual EEDI of a ship, CO2 emissions/transport work) incorporates all innovative technologies by including propulsion power from the main engine, auxiliary engine(s), energy efficient power generation and auxiliary propulsion (e.g. wind propulsion).

Reduction Factors are in place for reducing ship emissions depending on the implementation phase. Each phase sees reductions of 10% below the reference line.

– Source: International Maritime Organization –

Part of MARPOL Annex VI, entered into force 2013.

Requires all ships of 400 gt and above to carry a specific Ship Energy Efficiency Management Plan (SEEMP), the operational energy efficiency measure of the IMO.

– Source: International Maritime Organization –

Part of MARPOL Annex VI, entered into force 2013.

An International Energy Efficiency (IEE) Certificate for the ship shall be issued after a survey in accordance with the provisions of regulation 5.4 to any ship of 400 gross tonnage and above, before that ship may engage in voyages to ports or offshore terminals under the jurisdiction of other Parties.

IEE Certificate is valid throughout the lifetime of a ship unless there is a major conversion or change of flag or ship withdrawal from service.

Requires Port State Control (PSC) to conduct energy efficiency inspections. The IEE certificate is the starting point for any PSC inspection. Any port State inspection shall be limited to verifying, when appropriate, that there is a valid International Energy Efficiency Certificate on board.

– Source: International Maritime Organization –

Part of MARPOL Annex VI, entered into force 2018.

Requires ships of 5,000 GT and above to collect consumption data for each type of fuel oil they use, as well as other, additional, specified data including proxies for transport work. The aggregated data is reported to the flag State after the end of each calendar year and the flag State issues a Statement of Compliance to the ship.

– Source: International Maritime Organization –

The EU Monitoring, Reporting and Verification (MRV) Regulation requires ships of 5,000 gross tonnage and above calling at ports within the European Economic Area to monitor, report and verify their greenhouse gas emissions on a per-voyage and annual basis.

The regulation applies to CO₂ emissions from fuel consumption during voyages between EEA ports, as well as voyages to and from non-EEA ports where 50% of emissions are accounted for. It also covers emissions occurring while ships are at berth in EEA ports.

From 2024 onwards, the scope of the MRV framework has been expanded beyond carbon dioxide to include methane (CH₄) and nitrous oxide (N₂O), aligning the regulation with full greenhouse gas accounting and ensuring consistency with the EU Emissions Trading System for maritime transport.

The MRV system provides verified emissions data that supports transparency, benchmarking of vessel performance, and the implementation of further regulatory measures aimed at reducing greenhouse gas emissions from shipping.

In July 2023, the International Maritime Organization (IMO) adopted its revised Strategy on the Reduction of GHG Emissions from Ships, strengthening the global framework guiding the decarbonisation of international shipping.

The strategy sets an ambition to reach net-zero GHG emissions from international shipping by or around 2050, with indicative checkpoints for 2030 and 2040 to assess progress and guide further policy development. These checkpoints are intended to ensure that emissions from the sector peak as soon as possible and decline progressively over time.

The 2023 Strategy builds on the initial IMO GHG Strategy adopted in 2018 but reflects increased urgency and a stronger alignment with global climate objectives. It also provides the foundation for the development of mid-term measures at IMO level, which are expected to combine technical standards and economic mechanisms aimed at accelerating emissions reductions across the global fleet.

The strategy applies to international shipping and therefore plays a central role in shaping long-term investment decisions in vessel design, energy systems, and fuel pathways. It signals the direction of future regulatory tightening and the increasing importance of technologies capable of delivering substantial and sustained reductions in greenhouse gas emissions over the operational lifetime of vessels.

– Source: International Maritime Organization (IMO) –

Following the adoption of the 2023 IMO GHG Strategy, the International Maritime Organization is developing a set of mid-term measures aimed at further reducing greenhouse gas emissions from international shipping. These measures are expected to combine technical standards with economic mechanisms within a global regulatory framework.

The objective is to establish internationally agreed instruments that complement existing short-term efficiency measures and provide a predictable pathway for emissions reductions across the global fleet. The discussions include options for fuel-intensity requirements and potential market-based mechanisms designed to incentivise the uptake of low- and zero-emission energy systems.

While no final measure has yet been adopted, this ongoing work programme represents a central element of future international shipping regulation and will play a key role in shaping long-term investment decisions in vessel design, propulsion technologies, and energy supply chains.

– Source: International Maritime Organization (IMO) –

The International Maritime Organization is developing lifecycle assessment (LCA) guidelines for marine fuels to ensure that greenhouse gas emissions are evaluated on a full well-to-wake basis. This framework aims to account for emissions generated across the entire fuel production, distribution, and onboard use chain, rather than considering only emissions from combustion onboard ships.

The development of lifecycle fuel guidelines supports the implementation of the IMO 2023 GHG Strategy and will provide a methodological foundation for future fuel standards and market-based measures. By establishing consistent approaches to lifecycle emissions accounting, the framework will enable the comparative assessment of different marine energy carriers based on their overall climate impact.

While not a standalone regulatory requirement, the LCA framework is expected to underpin future IMO measures addressing fuel intensity and emissions reductions, thereby influencing long-term fuel pathway decisions and the deployment of zero-emission energy systems across the maritime sector.

– Source: International Maritime Organization (IMO) –

The Energy Efficiency Existing Ship Index (EEXI) is a technical measure adopted by the International Maritime Organization to improve the energy efficiency of ships already in service. It applies to most existing vessels of 400 gross tonnage and above engaged in international voyages.

The EEXI establishes a required energy efficiency level expressed in grams of CO₂ per tonne-mile, calculated based on the ship’s design parameters, engine power, and fuel consumption characteristics. Each vessel must demonstrate that its attained EEXI meets or exceeds the required value set for its ship type and size category.

Compliance may require technical or operational modifications, such as engine power limitation, propulsion upgrades, or improvements to hull and propeller performance. The measure entered into force in 2023 and forms part of the IMO’s short-term measures aimed at reducing greenhouse gas emissions from the existing fleet.

The EEXI provides a baseline design efficiency requirement for ships already in operation and works in conjunction with operational measures, such as the Carbon Intensity Indicator (CII), to drive continuous improvements in vessel energy performance over time.

– Source: International Maritime Organization (IMO) –

The Carbon Intensity Indicator (CII) is an operational measure adopted by the International Maritime Organization to assess and regulate the annual carbon intensity performance of ships in operation. It applies to cargo, Ro-Ro, and cruise ships of 5,000 gross tonnage and above engaged in international voyages.

The CII measures the amount of CO₂ emitted per transport work, typically expressed in grams of CO₂ per tonne-mile, and assigns each vessel an annual rating from A (best performance) to E (worst performance). The required carbon intensity levels become progressively stricter over time, driving continuous improvements in operational efficiency.

Ships rated D for three consecutive years, or rated E in a single year, are required to develop and implement a corrective action plan as part of their Ship Energy Efficiency Management Plan (SEEMP). These plans must outline the measures the vessel will take to achieve the required performance levels in subsequent years.

The CII entered into force in 2023 as part of the IMO’s short-term measures to reduce greenhouse gas emissions from international shipping. It complements technical efficiency measures such as the EEXI by focusing on operational performance and incentivising improvements in speed optimisation, voyage planning, energy management, and the adoption of lower-emission energy systems over the vessel’s operational lifetime.

– Source: International Maritime Organization (IMO) –

The Energy Efficiency Design Index (EEDI) Phase 3 represents the most stringent stage of the IMO’s design efficiency requirements for new ships. It applies to newly built vessels and establishes progressively tighter limits on the amount of CO₂ emissions permitted per transport work, expressed in grams of CO₂ per tonne-mile.

Phase 3 significantly strengthens the efficiency standards compared to earlier phases by requiring substantial reductions in design energy consumption across most ship types. The exact reduction levels vary depending on vessel category and size, reflecting differences in operational profiles and technical feasibility.

These requirements are achieved through improvements in hull form optimisation, propulsion efficiency, waste heat recovery, alternative propulsion concepts, and the integration of lower-emission energy systems. The measure therefore directly influences newbuild vessel design choices and encourages the uptake of advanced efficiency technologies at the design stage.

EEDI Phase 3 entered into force on a phased timeline beginning in 2022 for several ship categories, with broader application thereafter. It forms part of the IMO’s framework of technical measures aimed at improving the energy efficiency of new ships and supporting long-term reductions in greenhouse gas emissions from the global fleet.

– Source: International Maritime Organization (IMO) –

The revision of the Energy Taxation Directive (ETD) is a legislative proposal by the European Commission aimed at aligning energy taxation with the European Union’s climate and energy objectives. The proposal seeks to restructure minimum tax rates based on the energy content and environmental performance of fuels, replacing the existing volume-based approach.

For the maritime sector, the revision could progressively remove tax exemptions for fossil marine fuels used on intra-EU voyages, thereby introducing a fiscal signal favouring lower-emission and zero-emission energy carriers. By linking taxation levels to environmental performance, the directive aims to support the transition towards cleaner propulsion and energy systems across transport modes, including shipping.

The ETD revision remains under negotiation within the EU legislative process and has not yet entered into force. Its final scope, timelines, and specific application to maritime fuels will depend on the outcome of ongoing discussions between Member States and EU institutions.

If adopted, the directive is expected to influence long-term fuel cost structures and investment decisions in vessel energy systems, particularly for operators engaged in intra-European trade.

– Source: European Commission – Proposal for revision of the Energy Taxation Directive –

Shipping has been included in the European Union Emissions Trading System (EU ETS) from 1 January 2024, extending the EU’s carbon pricing mechanism to maritime transport. The system applies to cargo and passenger ships of 5,000 gross tonnage and above calling at ports within the European Economic Area.

The EU ETS covers carbon dioxide (CO₂) emissions from voyages between EEA ports, as well as 50% of emissions from voyages to and from non-EEA ports, and emissions generated while ships are at berth in EEA ports. The scope is expected to expand over time to include additional greenhouse gases, such as methane (CH₄) and nitrous oxide (N₂O), ensuring alignment with broader EU climate legislation.

The obligation to surrender emission allowances is being introduced progressively:

• 2024: 40% of verified emissions
• 2025: 70%
• 2026 onwards: 100%

By placing a price on greenhouse gas emissions, the EU ETS introduces a direct economic incentive to improve operational efficiency, adopt lower-emission energy systems, and accelerate the uptake of zero-emission technologies. The mechanism is intended to complement technical efficiency regulations and to drive long-term investment decisions across fleets, ports, and energy supply chains.

– Source: European Union – Directive (EU) 2023/959 –

FuelEU Maritime is a European Union regulation applying from 1 January 2025 that establishes progressively tightening limits on the greenhouse gas intensity of energy used onboard ships calling at EU ports. The regulation applies to ships of 5,000 gross tonnage and above and covers emissions from voyages within the European Economic Area, as well as a portion of emissions from voyages to and from non-EEA ports.

The framework is technology-neutral but designed to encourage the adoption of lower-emission and zero-emission energy carriers and propulsion systems over time. Compliance is assessed based on the lifecycle greenhouse gas intensity of the energy used onboard, creating a direct regulatory driver for cleaner fuels, electrification, and advanced energy management systems.

FuelEU Maritime complements the EU Emissions Trading System by regulating the carbon intensity of onboard energy use, thereby addressing both operational emissions costs and long-term fuel pathway choices within the European maritime sector.

– Source: European Union – Regulation (EU) 2023/1805 –

The European Union is introducing requirements for the use of onshore power supply (shore-side electricity) by certain ship categories while at berth in major EU ports. These requirements aim to eliminate emissions generated by auxiliary engines during port stays by enabling vessels to connect to electricity supplied from shore-based energy systems.

The measure supports the reduction of greenhouse gas emissions and air pollutants in port areas and encourages the integration of ship energy systems with port electrification infrastructure. It is particularly relevant for passenger and container vessels with regular port calls, where the availability of shore power can significantly reduce overall lifecycle emissions.

The implementation of shore power requirements forms part of the broader EU regulatory framework promoting electrification and zero-emission operation within maritime transport and associated port ecosystems.

– Source: European Union – Alternative Fuels Infrastructure Regulation (AFIR) –

The International Maritime Organization has adopted a ban on the use and carriage of heavy fuel oil (HFO) as fuel by ships operating in Arctic waters, as an amendment to MARPOL Annex I. The measure aims to reduce the environmental risks associated with potential oil spills and the emission of black carbon in the sensitive Arctic marine environment.

The ban applies to ships operating in Arctic waters, with certain exemptions and waivers during an initial implementation period to allow operators and flag States to adapt. The measure is being phased in, with full application expected after the transitional provisions expire.

By restricting the use of high-polluting residual fuels in Arctic regions, the regulation contributes to reducing local environmental impacts and encourages the adoption of cleaner marine fuels and alternative propulsion solutions. It also aligns with broader international efforts to protect polar ecosystems and limit short-lived climate pollutants that accelerate ice melt.

– Source: International Maritime Organization (IMO) –

The Mediterranean Sea has been designated as a Sulphur Emission Control Area (SECA) under MARPOL Annex VI, introducing stricter limits on the sulphur content of marine fuels used by ships operating in the region.

Under the SECA requirements, ships must use fuel with a sulphur content not exceeding 0.10% m/m, or apply equivalent emission abatement technologies that achieve the same reduction in sulphur oxide (SOx) emissions. The designation entered into force on 1 May 2025, significantly tightening air pollution controls across one of the world’s busiest maritime regions.

The Mediterranean SECA aims to reduce sulphur oxide emissions from shipping, improving air quality and reducing environmental and health impacts in coastal states. While primarily targeting air pollutants rather than greenhouse gases, the regulation contributes to the broader tightening of environmental performance requirements affecting ship fuel selection and onboard energy systems.

– Source: International Maritime Organization (IMO) –

Norway is implementing zero-emission requirements for vessels operating in its designated World Heritage Fjords, aiming to eliminate emissions that impact the fragile local environment and cultural landscape. The regulation forms part of Norway’s national strategy to reduce pollution from maritime tourism and transport in environmentally sensitive areas.

The requirements are being introduced on a phased basis, beginning in 2026 for certain vessel categories, with broader application planned in subsequent years. Compliance will require vessels operating in these fjords to adopt propulsion and energy systems capable of zero-emission operation during navigation and while at berth within the regulated areas.

The measure represents one of the first geographically defined regulatory regimes mandating zero-emission maritime operation. It therefore provides an important real-world framework for the deployment and demonstration of zero-emission vessel technologies in regular commercial service.

– Source: Norwegian Government / Norwegian Maritime Authorities –

Following the adoption of the 2023 IMO GHG Strategy, the International Maritime Organization is developing a set of mid-term measures to further reduce greenhouse gas emissions from international shipping. These measures are expected to combine technical requirements and economic mechanisms within a global regulatory framework.

Among the options under discussion are market-based measures intended to create an economic incentive for emissions reduction, potentially including a global carbon pricing instrument. However, no specific mechanism, price level, or implementation timeline has yet been adopted.

The ongoing work at IMO aims to establish internationally agreed measures that complement existing technical efficiency regulations and support the long-term objective of reducing greenhouse gas emissions from shipping in line with the 2023 Strategy.

– Source: International Maritime Organization (IMO) –

The Ocean-Based Climate Solutions Act is a proposed legislative framework introduced in the United States to support the deployment of ocean-based measures that contribute to climate mitigation and adaptation. The proposal includes provisions aimed at accelerating research, development, and demonstration of low- and zero-emission maritime technologies, as well as enhancing the resilience of marine ecosystems to climate change.

Within the shipping context, the Act envisages federal support for the development and deployment of cleaner vessel technologies, port infrastructure improvements, and innovation programmes focused on reducing greenhouse gas emissions from maritime transport. It also highlights the role of maritime decarbonisation in achieving broader national climate objectives.

The Act remains proposed legislation and has not been enacted into law. Its potential impact on maritime regulation will depend on the scope of final legislative adoption and the implementation of any associated funding or regulatory measures at federal level.

– Source: United States Congress (proposed legislation) –

The Clean Shipping Act of 2022 is proposed legislation introduced in the United States Congress aimed at reducing greenhouse gas emissions from ocean-going vessels operating in US waters and calling at US ports. The proposal seeks to establish progressively tightening emissions standards for maritime transport, ultimately targeting zero-emission operation for certain vessel classes over time.

The Act outlines a regulatory pathway that would require ships to meet defined lifecycle greenhouse gas intensity limits, supported by the development of low- and zero-emission vessel technologies and associated fuel infrastructure. It also proposes the establishment of federal programmes to support innovation, deployment, and the early adoption of compliant vessel and energy system solutions.

As proposed legislation, the Clean Shipping Act has not been enacted into law, and its final scope, timelines, and enforcement mechanisms remain subject to the US legislative process. If adopted, it could significantly influence technology deployment and emissions standards applicable to vessels operating within US jurisdiction.

– Source: United States Congress (proposed legislation) –

The Mediterranean Sea has been designated as a Nitrogen Oxides (NOx) Emission Control Area under MARPOL Annex VI, introducing stricter limits on nitrogen oxide emissions from marine engines operating in the region. The designation applies to new ships constructed on or after the applicable entry-into-force date and requires compliance with IMO Tier III NOx emission standards.

The measure aims to reduce emissions of nitrogen oxides that contribute to air pollution, eutrophication, and adverse impacts on coastal and marine ecosystems. While primarily targeting air pollutant emissions rather than greenhouse gases, the NOx ECA designation forms part of the broader tightening of environmental performance requirements for ships operating in sensitive maritime regions.

The implementation of Tier III standards in the Mediterranean region aligns with similar emission control regimes established in other designated ECAs and contributes to harmonising international regulatory approaches to ship engine emission performance.

– Source: International Maritime Organization (IMO) –

Aims to increase the use of sustainable alternative fuels in European shipping and ports from 2025 by imposing strict limits on the fuel’s life-cycle carbon intensity in 5-year increments until 2050, when carbon intensity should be 75% compared to the 2020 base year. It covers all energy used on board when the ship is at an EU port and on voyages between EU ports, and 50% of the energy used on voyages departing from or arriving to an EU port.

Applies to all vessels above 5000 GT of any flag sailing in except fishing vessels.

From 2030, container ships and passenger ships at EU ports will also have to connect to onshore power supply (OPS) and use it for all energy needs while at berth, with some exceptions.

– Source: European Commission –

China has established a national Emissions Trading Scheme (ETS) as part of its broader climate policy framework, initially covering selected industrial sectors with the objective of progressively expanding its scope over time. The system introduces a carbon pricing mechanism designed to limit greenhouse gas emissions by setting caps and allowing regulated entities to trade emission allowances.

While the current ETS does not yet fully cover the maritime transport sector, discussions and policy developments indicate a potential future extension to additional sectors, including shipping-related activities and port operations. Such an expansion would introduce a carbon cost signal affecting maritime transport within Chinese jurisdiction and along associated logistics chains.

The future application of emissions trading mechanisms to maritime transport in China would influence fuel choices, operational efficiency measures, and the deployment of lower-emission vessel technologies. However, the precise scope, timelines, and regulatory obligations for the shipping sector remain under development.

– Source: Ministry of Ecology and Environment of the People’s Republic of China – National Emissions Trading Scheme framework –

The United States Nationally Determined Contribution (NDC) under the Paris Agreement sets out the country’s overarching greenhouse gas emissions reduction targets across all sectors of the economy. The NDC reflects national climate commitments and informs the development of sector-specific policies, including those affecting maritime transport and port operations.

While the NDC itself does not constitute a maritime regulatory instrument, it provides the strategic policy framework guiding future emissions reduction measures and legislative initiatives that may influence the decarbonisation of the shipping sector.

– Source: United Nations Framework Convention on Climate Change (UNFCCC) –

Taxes on greenhouse gas emissions in all sectors have been proposed by a number of US senators. They include:

• MARKET CHOICE Act, 2019 (H.R.4520. Fitzpatrick): Transfers specified revenue from the tax to a Rebuilding Infrastructure and Solutions for the Environment Trust Fund (RISE Trust Fund) established by the bill, and other bodies.
• Energy Innovation and Carbon Dividend Act, 2019 (H.R.763. Deutch): A fee equal to the GHG fuel content multiplied by a carbon fee rate beginning at $15 and increasing by $10 each year. It would be imposed on the producers or importers of fossil fuels, subject to adjustment depending on progress in meeting emission targets. Also imposes a specified fee on fluorinated GHGs, such as those emitted by gas tankers and refridgerated carriers (according to the EPA). The bill includes border adjustment provisions that require certain fees or refunds for carbon-intensive products that are exported or imported. Revenue would go to a Carbon Dividend Trust Fund.
• • Stemming Warming and Augmenting Pay (SWAP) Act, 2019 (H.R.4058. Rooney): Imposes a $30 per metric ton of CO2-e increasing by 5% plus inflation each year and increasing by $3 per ton every two years if the previous year’s emission goals are not met. The revenue is divided: 70% for the reduction of payroll taxes; 10% for additional payments to Social Security beneficiaries; and 20% to establish a carbon trust fund.

– Source: United States Congress –

China has introduced a range of national and regional policy initiatives aimed at reducing emissions from coastal shipping and encouraging the adoption of lower-emission marine fuels and propulsion technologies. These measures form part of broader efforts to improve air quality in coastal regions and to align maritime transport with national climate and environmental objectives.

The evolving policy framework includes guidance on the promotion of cleaner marine fuels, electrification of short-sea and inland vessels, and the development of supporting infrastructure in key port regions. Implementation approaches vary across provinces and port authorities, reflecting regional priorities and pilot programmes targeting emission reductions from domestic coastal fleets.

While no single unified regulation currently mandates the use of specific low-carbon fuels for all coastal shipping, the cumulative effect of these initiatives is to create an increasingly supportive policy environment for lower-emission and zero-emission vessel technologies in Chinese coastal waters. The precise scope and timelines of binding requirements remain subject to ongoing national and regional policy development.

– Source: Ministry of Transport of the People’s Republic of China; Ministry of Ecology and Environment; supporting analysis by ICCT –