MARPOL: What You Need to Know

MARPOL, short for Marine Pollution, is the leading international convention governing the prevention of pollution from ships. 

It is the most comprehensive framework ever established to protect the marine environment from both accidental discharges, such as oil spills, and routine operational pollution, including sewage, garbage, and exhaust emissions. 

Its scope is deliberately broad, covering every major source of ship‑related pollution and setting out technical standards, operational requirements and enforcement mechanisms that apply worldwide.

This article will look at the MARPOL, covering its history, annexes, and compliance methodologies.

What are the origins of MARPOL?

The concept of MARPOL builds upon earlier attempts to regulate pollution, most notably OILPOL 54, which focused narrowly on tank cleaning operations.

However, it was the catastrophic Torrey Canyon oil spill in 1967 that exposed the inadequacy of existing measures and galvanised the international community to act. 

In response, the International Maritime Organisation (IMO) adopted MARPOL in 1973, later strengthened by the Protocol of 1978 before the convention entered into force in 1983.

Since then, MARPOL has become a truly global program. By 2022, it had been ratified by 150 countries, representing more than 98% of the world’s merchant shipping tonnage. This near‑universal adoption reflects both the scale of the environmental challenge and the recognition that shipping, as a global industry, requires harmonised international rules.

MARPOL has fundamentally changed the way shipping interacts with the environment. Where once the oceans were treated as limitless dumping grounds, they are now subject to strict regulation, with ships required to meet detailed technical standards and maintain extensive documentation. 

The convention continues to evolve, ensuring that maritime operations are aligned with modern expectations of environmental stewardship and sustainability.

What are the six annexes of MARPOL?

There are six separate annexes to the MARPOL regulations, each addressing a different pollutant. Together, they provide a comprehensive regulatory framework that governs vessel design, equipment, operations, and documentation. These annexes are as follows:

Annex I: Prevention of Pollution by Oil

Annex I is the most comprehensive of the annexes, dealing with oil pollution from machinery spaces and cargo operations on tankers. 

Structurally, Annex I is divided into multiple chapters covering definitions, surveys and certification, requirements for machinery spaces and oil tankers, operational discharge criteria, and Special Area provisions. 

Chapter II, which addresses survey and certification, applies to oil tankers of 150 GT and above and other ships of 400 GT and above, and establishes the basis for the issuance, validity, and endorsement of the International Oil Pollution Prevention Certificate.

Entered into force on the 2nd October 1983, this annex has shaped the design and operation of modern shipping, particularly in relation to tanker construction and machinery space equipment.

All new oil tankers of 5,000 tonnes deadweight and above must be constructed with double hulls or equivalent protective measures, a requirement introduced to reduce the risk of catastrophic spills in the event of a grounding or collision. 

Ships are also fitted with oily water separators (OWS), which ensure that any discharge of machinery space bilge water contains no more than 15 parts per million (ppm) of oil. Tankers must carry oil discharge monitoring and control systems, which continuously measure effluent and automatically stop discharges if limits are exceeded.

To comply, vessels must hold an International Oil Pollution Prevention Certificate (IOPP), valid for five years and subject to intermediate and annual surveys. 

Operationally, ships must maintain an Oil Record Book, divided into two parts:

• Part I - machinery space operations
• Part II - cargo/ballast operations for tankers

Every oil transfer, discharge, or disposal must be logged, and the book retained for at least three years. 

In addition, every vessel must carry a Shipboard Oil Pollution Emergency Plan (SOPEP), which sets out procedures for responding to oil pollution incidents and provides contact details for coastal authorities.

Discharge regulations are strict. Oil or oily mixtures may only be discharged if the vessel is en route, the oil content does not exceed 15 ppm, and the discharge passes through approved equipment. 

In Special Areas such as the Mediterranean, Baltic, Red Sea, Gulf areas and Antarctic, discharges are subject to even stricter prohibitions, often requiring zero discharge.

Annex II: Control of Pollution by Noxious Liquid Substances in Bulk

Brought into force on the 2nd October 1983, Annex II regulates the carriage and discharge of noxious liquid substances (NLS) transported in bulk, primarily on chemical tankers. 

Annex II is structured around the categorisation of NLS, tank design and equipment requirements, discharge standards, and survey and certification obligations. 

It sets out detailed operational controls through its chapters, including mandatory procedures for cargo residues, tank washing, and prewash requirements, and establishes certification requirements for chemical tankers to demonstrate compliance with approved carriage and discharge arrangements.

Its framework is based on categorisation of substances according to their environmental hazard. 

Substances are divided into four categories: 

• Category X - presents a major hazard if NLS is discharged into the sea
• Category Y - presents a moderate hazard if NLS is discharged into the sea
• Category Z - presents a minor hazard if NLS is discharged into the sea
• Other Substances (OS) - presents no hazard if discharged into the sea

Chemical tankers must carry a Procedures and Arrangements Manual, approved by the flag state, detailing how cargo residues and tank washings will be handled. 

Stripping limits apply, requiring tanks to be designed to minimise residues, with maximum permissible quantities defined by regulation.

Prewash procedures are required in ports for certain substances, so that residues are discharged to reception facilities rather than at sea. Discharge of residues is prohibited within 12 nautical miles of land.

For Category X substances, discharge into the sea is prohibited entirely. Residues must be delivered to reception facilities. Category Y and Z substances may be discharged under controlled conditions, subject to dilution and distance requirements.

Annex III: Prevention of Pollution by Harmful Substances in Packaged Form

Annex III addresses harmful substances carried in packaged form, including containers, portable tanks and vehicles. It is organised to regulate the packaging, marking, labelling, documentation, and stowage of harmful substances carried in packaged form. 

Entered into force on the 1st July 1992, Annex III is aligned with the International Maritime Dangerous Goods (IMDG) Code, which defines “marine pollutants” and sets standards for cargo documentation, packaging standards, and inspection by port state authorities.

Packages must be durable enough to withstand three months’ immersion in the sea without loss of integrity. Clear labelling is required, including the marine pollutant symbol, so that substances are identifiable even if lost overboard. 

Cargo must be stowed to minimise environmental risk while maintaining ship safety, and segregation rules apply to prevent incompatible substances being stored together.

Operational compliance is achieved through documentation and inspection. Port State Control may verify compliance with packaging and labelling requirements, and documentation must accompany all shipments to ensure traceability and accountability.

Annex IV: Prevention of Pollution by Sewage from Ships

Brought into force on the 27th September 2003, Annex IV regulates the discharge of sewage, recognising its impact on coastal waters, ecosystems and public health. 

Its chapters establish the technical requirements for sewage treatment plants, holding tanks, and comminuting and disinfecting systems, alongside survey and certification procedures supporting the issuance and continued validity of the International Sewage Pollution Prevention Certificate.

Ships of 400 gross tonnage and above, or those certified to carry more than 15 persons, must hold an International Sewage Pollution Prevention Certificate (ISPPC).

Vessels must be fitted with approved sewage treatment plants, comminuting/disinfecting systems, or holding tanks. The rules for treated versus untreated sewage differ:

• Treated sewage may be discharged at sea via an approved treatment plant, while comminuted and disinfected sewage may be discharged more than three nautical miles from land
• Untreated sewage may only be discharged more than 12 nautical miles offshore, while the vessel is en route at sufficient speed

Special Areas such as the Baltic Sea impose stricter rules, including complete prohibition of untreated sewage discharge. These measures ensure that sewage disposal does not compromise water quality or coastal ecosystems, particularly in areas of high traffic or tourism.

Annex V: Prevention of Pollution by Garbage from Ships

Annex V governs the disposal of garbage, including plastics, food waste, cargo residues and other solid materials.

The annex places particular emphasis on operational controls, requiring ships to maintain garbage management plans, display placards, and complete Garbage Record Books, rather than relying primarily on technical equipment or ship-specific certification.

Entered into force on the 31st December 1988, this annex is notable for its outright ban on the disposal of plastics at sea, due to their long‑lasting and harmful impact on marine life.

Other forms of garbage are subject to restrictions based on type, distance from land and Special Area designation. 

Ships must carry a Garbage Management Plan, tailored to the vessel’s operations, outlining procedures for collection, storage, and disposal. Placards must be displayed in working languages plus English, French or Spanish, informing crew and passengers of discharge restrictions. A Garbage Record Book must also be maintained, documenting all disposal operations and retained for two years.

Garbage is categorised into plastics, food waste, domestic waste (paper, rags, glass, metal), cargo residues, animal carcasses, and cleaning agents/additives (subject to biodegradability standards). The table below lists the different permissions:

Garbage type	Disposal outside special areas	Disposal in special areas	Offshore platforms (more than 12 nm from land) and all ships within 500 m of such platforms
Food waste (comminuted or ground)	Permitted if nearest land is more than 3 nm away	Permitted if nearest land is more than 12 nm away	Permitted
Food waste (not comminuted or ground)	Permitted if nearest land is more than 12 nm away	Prohibited	Prohibited
Cargo residues* (not contained in wash waster)	Permitted if nearest land is more than 12 nm away	Prohibited	Prohibited
Cargo residues* (contained in wash waster)	Permitted if nearest land is more than 12 nm away	Permitted if nearest land is more than 12 nm away	Prohibited
Cleaning agents and additives* (contained in cargo hold wash water)	Permitted	Permitted if nearest land is more than 12 nm away	Prohibited
Cleaning agents and additives* (in deck and external surfaces wash water)	Permitted	Permitted	Prohibited
Carcasses of animals carried on board as cargo and which died during voyage	Permitted as far from the nearest land as possible and en route	Prohibited	Prohibited
All other garbage (plastics, synthetic ropes, fishing gear, cooking oil, etc)	Prohibited	Prohibited	Prohibited
Mixed garbage	When mixed or contaminated by other substances prohibited from discharge, or with different requirements, more stringent requirements apply

* Substances must not be harmful to marine environment

In Special Areas such as the Antarctic and Wider Caribbean, stricter prohibitions apply, often requiring zero discharge of certain categories.

Annex VI: Prevention of Air Pollution from Ships

Brought into force on the 19th May 2005, Annex VI extends MARPOL’s scope to atmospheric pollution, addressing emissions from ship exhausts and incinerators. 

Annex VI is structured to regulate fuel oil quality, engine emissions, energy efficiency measures, ozone-depleting substances, and shipboard incineration. This annex is increasingly important as shipping’s contribution to global air quality and climate change comes under scrutiny.

Its chapters establish survey and certification requirements for air pollution prevention, including the issuance of the International Air Pollution Prevention Certificate (IAPP), and provide the regulatory framework for emission limits, fuel verification, and ongoing energy efficiency obligations.

The global sulphur cap, introduced in 2020, limits sulphur content in fuel oil to 0.50%. In designated Emission Control Areas (ECAs), the limit is stricter at 0.10%. Ships must retain Bunker Delivery Notes for three years to demonstrate compliance.

Nitrogen oxide (NOx) emissions are regulated through Tier I, II and III standards, depending on engine installation date and operating area. Tier III standards apply in ECAs, requiring advanced emission control technologies. The table below outlines the NOx limitations:

Tier	Ship Built	NOx Limit, g/kWh
		RPM <130	130 ≤ RPM < 2000	RPM ≧ 2000
Tier I	< 2010	17.0	45 ∙RPM ⁻º∙²º	9.8
Tier II	> 2011	14.4	45 ∙RPM ⁻º∙²³	7.7
Tier III	> 2016	3.4	45 ∙RPM ⁻º∙²º	1.96

Greenhouse gas measures include the Energy Efficiency Design Index (EEDI), mandatory for new ships, and the Ship Energy Efficiency Management Plan (SEEMP), required for all ships.

The Carbon Intensity Indicator (CII) is under development, designed to indicate annual efficiency of ships in service. 

Annex VI also prohibits new installations containing ozone‑depleting substances (ODS) such as halons and chlorofluorocarbons, and regulates shipboard incinerators, banning the disposal of incinerator ash overboard.

How is MARPOL regulated?

MARPOL is a framework that requires ships to demonstrate compliance through surveys, certification and meticulous record‑keeping. These measures are designed to ensure that the regulations are actively enforced across the global fleet.

Every vessel subject to MARPOL must undergo a series of surveys to verify that its construction, equipment and operational practices meet the convention’s requirements. These include:

• Initial surveys - conducted before a ship enters service, to confirm compliance from the outset
• Renewal surveys - carried out at prescribed intervals to maintain certification
• Intermediate and annual surveys - which provide ongoing assurance that standards are upheld

Successful completion of these inspections leads to the issuance of certificates such as the International Oil Pollution Prevention Certificate (IOPP) under Annex I and the IAPP under Annex VI. 

These documents are essential for demonstrating compliance during port inspections and are recognised internationally. Ships must maintain detailed logs that allow inspectors to verify operations retrospectively:

• Oil record books - required under Annex I, these must record all oil transfer and disposal operations and be retained for at least three years
• Garbage record books - required under Annex V, these document the handling and disposal of garbage and must be kept for two years
• Bunker delivery notes - under Annex VI, ships must retain fuel oil receipts for three years to prove sulphur content compliance

Maintaining these records provides transparency and accountability, meaning that crews follow procedures and that violations can be detected even after the fact.

Special Areas under MARPOL annexes

MARPOL designates certain sea regions as ‘Special Areas’ due to their oceanographic or ecological sensitivity. 

In these zones, discharge restrictions are far stricter than in general waters. These areas include:

Annex	Special areas
Annex I	Mediterranean Sea Baltic Sea Black Sea Red Sea Gulf area Gulf of Aden Antarctic Area North-West European Waters Oman Area of the Arabian Sea Southern South African Waters
Annex II	Antarctic Area
Annex III	No special areas applied
Annex IV	The Baltic Sea
Annex V	Mediterranean Sea Baltic Sea Black Sea Red Sea The Gulfs Area North Sea Antarctic Area (South of Latitude 60 deg South) Wider Caribbean Region (including the Gulf of Mexico and the Caribbean Seas)
Annex VI	Baltic Sea (SOX, NOx) North Sea (SOX, NOx) North American ECA (SOx, PM and NOx) United States and Caribbean Sea ECA (SOx, PM and NOx)

Additionally, there are currently 14 Particularly Sensitive Sea Areas (PSSA) which are defined by the MEPC as an area which requires special protection by IMO due to ecological, scientific, and socio-economic factors. These PSSAs are:

• Great Barrier Reef
• Archipelago of Sabana-Camague
• Sea Area around Malpelo Island
• Marine Area around the Florida Keys
• Wadden Sea
• Paracas National Reserve
• Western European Waters
• Torres Strait as an extension to GBR PSSA
• Canary Islands
• Galapagos Archipelago
• Baltic Sea Area
• Papahanaumo-kuakea Marine National Monument (North-western Hawaiian Islands)
• Strait of Bonifacio
• Saba Bank (Caribbean Island of Saba)

While designating areas as MARPOL Special Areas and Particularly Sensitive Areas certainly acts as a positive step in safeguarding these environments, it is certainly not enough as their implementation presents several challenges. Enforcement of MARPOL, therefore, remains an important factor.

Recent and upcoming amendments to MARPOL

MARPOL is not a static arrangement, and is continuously amended through the IMO’s Marine Environment Protection Committee (MEPC) to address emerging environmental risks, technological developments, and operational realities within the shipping industry.

One of the most significant recent changes was the IMO 2020 global sulphur cap, which reduced the maximum sulphur content of marine fuels from 3.50% to 0.50% m/m worldwide. This measure has delivered measurable improvements in air quality, particularly in port cities and coastal regions.

Further amendments are already in progress. Under IMO Resolution MEPC.392(82), new Sulphur Oxides (SOx) Emission Control Areas have been designated for the Norwegian Sea and the Canadian Arctic. 

Regulation 14 of MARPOL Annex VI will enter into force on 1st March 2026, with mandatory compliance from 1st March 2027, requiring ships operating in these areas to use fuel oil with a sulphur content not exceeding 0.10% m/m.

The IMO continues to expand the acceptance of electronic record books, allowing certain MARPOL logs to be maintained in approved digital formats. These changes are intended to improve transparency, reduce administrative burden, and support more effective compliance monitoring.

Shipowners and operators must therefore remain alert to ongoing amendments, as compliance requirements can change not only by annex, but also by operating area and implementation date.

How is MARPOL enforced?

MARPOL’s effectiveness depends not only on the regulations themselves, but also on enforcement and the provision of infrastructure to support compliance. Two mechanisms are central to this initiative: Port State Control (PSC) and reception facilities.

Port State Control (PSC) 

Port States have the authority to inspect foreign vessels visiting their ports to ensure their compliance with MARPOL annexes. These inspections typically focus on documentation, crew familiarity with procedures, and the condition of pollution‑prevention equipment. 

If deficiencies, such as incomplete Oil Record Books, improper Garbage Management Plans, or crew members unable to demonstrate knowledge of emergency procedures are found, the vessel may be detained until corrective action is taken.

PSC is a powerful enforcement tool because it ensures that compliance is not limited to flag states alone. Ships must meet international standards wherever they operate, and failure to do so can result in costly delays, reputational damage, and even prosecution. 

The system is coordinated through regional agreements such as the Paris MoU and Tokyo MoU, which establish uniform inspection procedures and share information on non‑compliant vessels.

Reception facilities 

A key element of MARPOL is that ships should not be forced to discharge waste at sea due to a lack of alternatives. 

To avoid such an incident, Member States are obliged to provide adequate shore‑based reception facilities for oil residues, noxious liquid substances, sewage, garbage, and ozone‑depleting substances. 

These facilities must be accessible, efficient, and capable of handling the types and volumes of waste generated by ships operating in their waters.

The availability of reception facilities is particularly critical in Special Areas, where discharge restrictions are most stringent. Without reliable facilities, compliance would be impractical. 

The IMO monitors the provision of such infrastructure, and deficiencies can be reported by shipowners or operators.

Together, PSC and reception facilities create a balanced enforcement framework. PSC makes sure that ships are held accountable for compliance, while reception facilities provide the practical means to comply. 

The challenges in enforcement

Despite its near-universal adoption, the effective implementation of MARPOL faces practical challenges arising from the inherently international nature of shipping. 

Flag State enforcement can vary significantly, particularly where vessels are registered under flags of convenience with limited inspection capacity or oversight resources.

As a result, Port State Control plays a critical role in ensuring that compliance is assessed independently of flag administration. However, inspection intensity and interpretation of deficiencies may still differ between regions, making consistent enforcement through regional Memoranda of Understanding essential.

Another ongoing challenge relates to the availability and adequacy of reception facilities, particularly in smaller ports or remote regions. Where facilities are limited or inefficient, compliance may become operationally difficult, underscoring the importance of continued investment by coastal states and effective reporting mechanisms within the IMO framework.

What are the steps for MARPOL compliance?

Effective MARPOL compliance requires more than technical equipment alone. Key measures include:

• Ensuring that all statutory certificates are valid and supported by completed surveys
• Maintaining accurate and up-to-date record books, whether paper-based or electronically approved
• Regularly reviewing and updating shipboard plans and manuals, including SOPEP, Garbage Management Plans, and SEEMP
• Providing routine crew training to ensure familiarity with discharge criteria and emergency procedures
• Monitoring IMO and flag state circulars for amendments affecting operating areas or certification requirements

Proactive compliance reduces the risk of detention, penalties, and reputational damage, while supporting environmental protection objectives.

Related IMO conventions and codes

MARPOL operates as part of a broader international regulatory framework governing maritime safety, environmental protection, and operational management. Key related instruments include:

• SOLAS (Safety of Life at Sea Convention) - oversees ship safety standards and equipment
• The Ballast Water Management Convention - addresses the transfer of invasive aquatic species
• The International Safety Management (ISM) Code - establishes safety and environmental management systems for ships and operators
• The International Maritime Dangerous Goods (IMDG) Code - regulates the carriage of dangerous goods in packaged form

Understanding how these instruments interact is essential for achieving holistic regulatory compliance across ship design, operation, and management.

What are the environmental and health benefits of MARPOL?

The regulatory controls established under MARPOL have delivered significant environmental and public health benefits over time.

Measures under Annex I have contributed to a long-term reduction in the frequency and severity of major oil spills, while Annex V has significantly curtailed the discharge of plastics and persistent waste into the marine environment.

More recently, controls introduced under Annex VI have led to measurable improvements in air quality, particularly in densely populated port regions. Reductions in sulphur oxide and particulate matter emissions have been linked to lower incidences of respiratory illness and improved public health outcomes in coastal communities.

The designation of Special Areas and Particularly Sensitive Sea Areas highlights the recognition that certain marine environments require enhanced protection due to their ecological, scientific, or socio-economic importance. In these regions, stricter discharge standards are applied to mitigate cumulative environmental harm and preserve vulnerable ecosystems.

Brookes Bell’s MARPOL Survey Expertise

With over a century of working with the maritime and energy industries, our multi-disciplinary team comprises chemical-tanker Master Mariners, accredited marine chemists, and senior surveyors, all supported by The Lab at Brookes Bell. 

Brookes Bell has developed a programme of MARPOL auditing which has been successfully delivered on numerous vessels. Our MARPOL audits include on-board surveys, which use a pragmatic, risk-based approach to identify both weak areas and strong areas in relation to current MARPOL guidelines.

In addition to our MARPOL audits, we are also able to develop a MARPOL compliance programme for your vessel.

We will provide on-board training to ships’ staff, as well as shore-based training to both senior seagoing and office-based management personnel to create a MARPOL compliance programme that will give you the reassurance you need in relation to MARPOL regulations.

If you need support navigating MARPOL regulations, Brookes Bell can help. Speak to us today for more information.

Contact Brookes Bell today 

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