The main type of “bunker” oil for ships is heavy fuel oil, derived as a residue from crude oil distillation. Crude oil contains sulphur which, following combustion in the engine, ends up in ship emissions. Sulphur oxides (SO_x) are known to be harmful to human health, causing respiratory symptoms and lung disease. In the atmosphere, SO_x can lead to acid rain, which can harm crops, forests and aquatic species, and contributes to the acidification of the oceans.

Limiting SO_x emissions from ships will improve air quality and protects the environment.

IMO regulations to reduce sulphur oxides (SO_x) emissions from ships first came into force in 2005, under Annex VI of the International Convention for the Prevention of Pollution from Ships (known as the MARPOL Convention). Since then, the limits on sulphur oxides have been progressively tightened.

From 1 January 2020, the limit for sulphur in fuel oil used onboard ships operating outside designated emission control areas will be reduced to 0.50% m/m (mass by mass). This will significantly reduce the number of sulphur oxides emanating from ships and should have major health and environmental benefits for the world, particularly for populations living close to ports and coasts.

Below you will find answers to some of the frequently asked questions about the sulphur limit.

You can also download a more detailed set of FAQ here. 

Symposium on IMO 2020 and Alternative Fuels (17-18 October 2019)

​IMO hosted a Symposium on IMO 2020 and Alternative Fuels to raise awareness and to take stock of the preparations for the IMO 2020 rule, and to discuss the role of alternative fuels in the decarbonization of international shipping. Presentations and audio files can be found here.

Limiting SOx emissions from ships will have a very positive impact on human health: how does that work?

Simply put, limiting sulphur oxides emissions from ships reduces air pollution and results in a cleaner environment. Reducing SO_x also reduces particulate matter, tiny harmful particles which form when fuel is burnt. 

A study on the human health impacts of SO_x emissions from ships, submitted to IMO’s Marine Environment Protection Committee (MEPC) in 2016 by Finland, estimated that by not reducing the SO_x limit for ships from 2020, the air pollution from ships would contribute to more than 570,000 additional premature deaths worldwide between 2020-2025. 

Why are ships already less harmful than other forms  of transport  

​Ships do emit pollutants and other harmful emissions. But they also transport large quantities of vital goods across the world’s oceans – and seaborne trade continues to increase. In 2016, ships carried more than 10 billion tons of trade for the first time, according to UNCTAD. 

So ships have always been the most sustainable way to transport commodities and goods. And ships increasingly becoming even more energy efficient. IMO regulations on energy efficiency support the demand for ever greener and cleaner shipping. A ship that is more energy-efficient burns less fuel so emits less air pollution.

It has sometimes been quoted that just a few ships (all using fuel oil with the maximum permitted sulphur content) emit as much harmful air pollutants as all the cars in the world (if the cars were all using the cleanest fuel available).

Not only is this the very worst-case scenario, but this does not take into account the amount of cargo that is being carried by those ships and the relative efficiency. It is important to consider the amount of cargo carried and the emissions per tonne of cargo carried, per kilometre travelled. Studies have shown that ships are by far the most energy-efficient form of transportation, compared with other modes such as aviation, road trucks and even railways.

It is also relevant to remember that shipping responds to the demands of world trade. As world trade increases, more ship capacity 

Do small ships have to comply with the sulphur limit from 2020?

​Yes, the MARPOL regulations apply to all ships. Only larger ships of 400 gross tonnage and above engaged in voyages to ports or offshore terminals under the jurisdiction of other Parties have to have an International Air Pollution Prevention Certificate, issued by the ship’s flag State. But all sizes of ships will need to use fuel oil that meets the 0.50% limit from 1 January 2020.

Some smaller ships may already be using fuel oil that meets the limit, such as a marine distillate suitable for their engines. (Small ships operating in the already-designated emission control areas will be using fuel oil that meets the 0.10% limit in those emission control areas.)

How can ships carry so much cargo so efficiently?

Ships are the largest machines on the planet and the world’s largest diesel engines can be found on cargo ships. These engines can be as tall as a four-storey house, and as wide as three London buses. The largest marine diesel engines have more than 100,000 horsepower (in comparison, a mid-sized car may have up to 300 horsepower). But the largest container ships can carry more than 20,000 containers and the biggest bulk carriers can carry more than 300,000 tons of commodities, like iron ore. 

So powerful engines are needed to propel a ship through the sea. And it is important to consider how much energy is used to carry each ton of cargo per kilometre.  When you look at the relative energy efficiency of different modes of transport, ships are by far the most energy-efficient.  

Ships can reduce air pollutants by being, even more, energy-efficient, so they burn less fuel and therefore their emissions are lower.

Are all types of scrubbers allowed under IMO rules?

​Yes, so long as they achieve the same level of emissions reduction.

Regulation 4 of MARPOL Annex VI allows for Administrations (flag States) to approve “equivalents” – any  “fitting, material, appliance or apparatus to be fitted in a ship or other procedures, alternative fuel oils, or compliance methods used as an alternative to that required”  – that enables the same standards of emission control to be met. 

For reduction of sulphur oxide emissions, some flag States have accepted and approved scrubbers – otherwise known as “Exhaust Gas Cleaning Systems”, as meeting the requirements for sulphur oxide reduction.

There is an important requirement in the same regulation on Equivalents, which says that in paragraph 4 “The Administration of a Party that allows the use of an equivalent …. shall endeavour not to impair or damage its environment, human health, property, or resources, or those of other States”.

IMO has adopted strict criteria for the discharge of wash water from EGCS. Any residues were generated by the EGC unit usually in a closed-loop configuration, should be delivered ashore to adequate reception facilities. Such residues should not be discharged to the sea or incinerated on board.

Open-loop scrubbers add water to the exhaust gas which turns sulphur oxides (SOx) into sulphates/sulphuric acid. Open-loop scrubbers return wash water to the sea. The wash water must meet strict criteria, so that discharge wash water should have a pH of no less than 6.5. There are also strict limits on the discharge of PAHs (Polycyclic Aromatic Hydrocarbons) and nitrates.

The guidelines, with the wash water criteria, (last revised and adopted in 2015), are currently under review in the IMO Sub-Committee on Pollution Prevention and Response (PPR).

Some Member States have raised environmental concerns about EGCS discharge and the Marine Environment Protection Committee (MEPC) at its last session in May 2019 asked the PPR Sub-Committee to look into “Evaluation and harmonization of rules and guidance on the discharge of liquid effluents from EGCS into waters, including conditions and areas”.

What is the current regulation on SOx in ships emissions and by how much is that going to be improved?

​We are going to see a substantial cut: to 0.50% m/m (mass by mass) from 3.50% m/m.

For ships operating outside designated emission control areas, the current limit for the sulphur content of ships’ fuel oil is 3.50% m/m.

The new limit will be 0.50% m/m which will apply on and after 1 January 2020.

There is an even stricter limit of 0.10% m/m already in effect in emission control areas (ECAS) which have been established by IMO. This 0.10% m/m limit applies in the four established ECAS: the Baltic Sea area; the North Sea area; the North American area (covering designated coastal areas off the United States and Canada); and the United States Caribbean Sea area (around Puerto Rico and the United States Virgin Islands). 

(Countries bordering the Mediterranean Sea are currently considering the possibility of applying to designate the Mediterranean Sea or parts thereof as an ECA. Read more here.)

Fuel oil providers already supply fuel oil that meets the 0.10% m/m limit (such as marine distillate and ultra-low sulphur fuel oil blends) to ships that require this fuel to trade in the ECAs.

What must ships do to meet the new IMO regulations?

The IMO MARPOL regulations limit the sulphur content in fuel oil. So ships need to use fuel oil which is inherently low enough in sulphur, in order to meet IMO requirements.

Refineries may blend fuel oil with a high (non-compliant) sulphur content with fuel oil with a sulphur content lower than the required sulphur content to achieve a compliant fuel oil. Additives may be added to enhance other properties, such as lubricity.

Some ships limit the air pollutants by installing exhaust gas cleaning systems, also known as “scrubbers”. This is accepted by flag States as an alternative means to meet the sulphur limit requirement. These scrubbers are designed to remove sulphur oxides from the ship’s engine and boiler exhaust gases. So a ship fitted with a scrubber can use heavy fuel oil, since the sulphur oxides emissions will be reduced to a level equivalent to the required fuel oil sulphur limit.

Ships can have engines that can use different fuels, which may contain low or zero sulphur. For example, liquefied natural gas, or biofuels.  

Why have some ports already banned the discharge of wash water?

​Some IMO Member States have taken a precautionary approach towards wash water discharge and have taken measures to limit or restrict discharge of wash water in their local ports and coastlines.

States have the right under UNCLOS to adopt their own laws and measures to reduce and control pollution of the marine environment from ships in their ports, internal waters and territorial seas.

Where can I find out which ships have EGCS or are using other equivalents?

​The IMO GISIS module on MARPOL annexe VI includes a list of notifications received from the IMO Member States in relation to Regulation 4.2 Equivalent compliance method. You can view the database here.  

Consistent compliance with the 0.50% limit is vital. What is IMO doing about that?

​Monitoring, compliance and enforcement of the new limit fall to Governments and national authorities of Member States that are Parties to MARPOL Annex VI. Flag States (the State of registry of a ship) and port States have rights and responsibilities to enforce compliance. IMO has adopted the 2019 Guidelines for port State control under MARPOL Annex VI Chapter 3 (download here). 

IMO is working with the Member States as well as industry (including the shipping industry and the bunker supply and refining industry) to identify and mitigate transitional issues so that ships may meet the new requirement.

For example, developing guidance, developing standardised formats for reporting fuel oil non-availability if a ship cannot obtain compliant fuel oil and considering verification and control issues.

The MEPC has issued guidance on ship implementation planning, part of a set of guidelines being developed by IMO for consistent implementation of the MARPOL regulation coming into effect from 1 January 2020. 

Guidance on best practices for fuel oil suppliers has also been issued. The Guidance is intended to assist fuel oil purchasers and users in assuring the quality of fuel oil delivered to and used onboard ships, with respect to both compliance with the MARPOL requirements and the safe and efficient operation of the ship. The guidance pertains to aspects of the fuel oil purchase up to the loading of the purchased fuel oil on board.

A full list of guidance and guidelines can be found on the infographic.

In October 2018, IMO’s Marine Environment Protection Committee (MEPC) adopted a MARPOL amendment to prohibit the carriage of non-compliant fuel oil for combustion purposes for propulsion or operation on board a ship – unless the ship has an exhaust gas cleaning system (“scrubber”) fitted. 

How can ship operators and owners plan ahead for the 0.50% sulphur 2020 limit?

​To assist ship operators and owners to plan ahead for the 0.50% sulphur 2020 limit, the MEPC has approved various guidelines and guidelines. 

The 2019 Guidelines on consistent implementation of 0.50% sulphur limit under MARPOL Annex VI adopted by resolution MEPC.320(74) are available here. 

These comprehensive guidelines include a template for a “Fuel Oil Non-Availability Report (FONAR)” set out in Appendix 1 and a “Technical review of identified possible potential safety implications associated with the use of 2020 compliant fuels” set out in appendix 2. 

Guidance on ship implementation planning (issued November 2018) can be downloaded here.

The ship implementation planning guidance includes sections on:

• risk assessment and mitigation plan (impact of new fuels);
• fuel oil system modifications and tank cleaning (if needed);
• fuel oil capacity and segregation capability;
• procurement of compliant fuel;
• fuel oil changeover plan (conventional residual fuel oils to 0.50% sulphur compliant fuel oil); and
• documentation and reporting.

See also outcome of MEPC 74 here.   

A joint industry group has also developed its own guidance, which IMO has shared with its Member States and international organizations in a circular letter. You can view the Joint Industry Guidance on the Supply and Use of 0.50% Sulphur Marine Fuel here. 

What is the “carriage ban” and how does it work?

​The carriage ban refers to the MARPOL amendment adopted in 2018 to prohibit the carriage of non-compliant fuel oil for combustion purposes for propulsion or operation on board a ship – unless the ship has an exhaust gas cleaning system (“scrubber”) fitted. 

The amendment is intended as an additional measure to support consistent implementation and compliance and provide a means for effective enforcement by States, particularly port State control. 

The specific provision requires that fuel oil used onboard ships shall not exceed 0.50% sulphur limit. The amended provision to prohibit the carriage of non-compliant fuel oil reads as follows: “The sulphur content of fuel oil used or carried for use onboard a ship shall not exceed 0.50% m/m.” 

So, carriage of fuel oil for use onboard ships will be prohibited from 1 March 2020 if the sulphur content exceeds 0.50%.

Regulation 2.9 of MARPOL Annex VI provides the definition for ‘fuel oil’ – “Fuel oil means any fuel delivered to and intended for combustion purposes for propulsion or operation on board a ship, including gas, distillate and residual fuels.”

The provision does not apply to fuel oil being carried as cargo.  

This MARPOL amendment will enter into force on 1 March 2020. The full text of the MARPOL amendment can be downloaded here. 

Will new fuels be needed to meet the 2020 limit? Will there be enough?

It is likely that new blends of fuel oil for ships will be developed, For example, a gas oil, with a very low sulphur content can be blended with heavy fuel oil to lower its sulphur content. ​ These new blends are likely to cost more initially than the “heavy fuel oil” bunkers (fuel) used by the majority of ships today.  Ships can also choose to switch to a different fuel altogether. Or they may continue to purchase heavy fuel oil, but install ”scrubbers” to reduce the output of SOx in order to have an equivalent means to meet the requirement. Of course, some ships are already using low sulphur fuel oil to meet the even more stringent limits of 0.10% m/m when trading in the already-established emission control areas. So those fuel oil blends suitable for ECAS, will also meet the 0.50% m/m limit in 2020. However, there is a cost differential, and these blends are more expensive than heavy fuel oil. A study commissioned by IMO into the “Assessment of fuel oil availability” concluded that the refinery sector has the capability to supply sufficient quantities of marine fuels with a sulphur content of 0.50% m/m or less and with a sulphur content of 0.10% m/m or less to meet demand for these products, while also meeting demand for non-marine fuels. The full study can be downloaded here.