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MARPOL 73/78: The Convention & Its Six Annexes

Master MARPOL 73/78: its six annexes, statutory equipment requirements, nautical distance discharge limits, special areas, certificates, and PSC audits.

By the Chartandkeel editorial team · Updated October 2026 · About our sources

Published by ChartandKeel Updated

1. What is MARPOL?

MARPOL is the International Convention for the Prevention of Pollution from Ships. Administered by the International Maritime Organization (IMO), it protects the sea and atmosphere from pollution caused by ships.

The convention was adopted in 1973 and modified by the 1978 Protocol after tanker disasters such as the Argo Merchant and Amoco Cadiz. The combined treaty is known as MARPOL 73/78. It entered into force on 2 October 1983.

Its six annexes cover different pollution sources. Together, they cover 99.5% of world tonnage.

MARPOL applies to all ships flying the flag of a State Party or operating under its authority, encompassing commercial cargo carriers, passenger liners, offshore support vessels, and fixed platforms. While naval vessels have sovereign immunity, Flag Administrations mandate that their fleets conform to MARPOL standards to the fullest extent practicable.

Prevention at source: Rather than compensating for damage after a spill, MARPOL sets construction standards (double hulls, segregated ballast tanks and closed loops), discharge restrictions, and record-keeping requirements.

Figure 1: Six MARPOL waste streams aboard shipPhysical ship cutaway locating engine and oil separator, sewage treatment plant, chemical tanks with a controlled underwater outlet, marked cargo containers, sorted garbage and food grinder, and engine exhaust catalyst and funnel.Six annexes · one shipboard environmentVI · EXHAUST Engine → SCR / funnelIII · PACKAGED CARGO Marked, stowed, segregatedV · GARBAGE Sort, retain; grind foodWaterlineI · OIL Bilge → 15 ppm OWS Sludge retained / landedIV · SEWAGE Toilets → approved STP Or retain in holding tankII · BULK CHEMICALS Washings / residues Underwater outlet controlRepresentative cutaway · sea discharge requires all applicable conditions.
Figure 1: Vessel Comprehensive Environmental Protection Architecture. Every shipboard waste stream is governed by an individual MARPOL Annex, routing effluent through statutory hardware: bilge oil through 15 ppm filtration (Annex I), chemical tank washings through underwater outlets (Annex II), packaged freight through IMDG segregation (Annex III), sanitary black water through certified STPs (Annex IV), solid garbage through comminutors (Annex V), and exhaust plumes through SOx/NOx abatement systems (Annex VI).

2. The Six Annexes in Order

For oral examinations and audits, learn the annexes in this order: oil, bulk chemicals, packaged harmful substances, sewage, garbage, air pollution.

Annex I — Oil

Controls operational oily waste and accidental spills: machinery-space bilge discharge (≤15 ppm), sludge handling, fuel bunkering, double-hull tanker construction, and cargo ballast monitoring.

Certificate: IOPP — International Oil Pollution Prevention Certificate.

Annex II — Noxious liquid substances in bulk

Controls chemicals carried in tankers, classified by marine hazard as X, Y, Z, and OS. Requirements include tank stripping limits (75 litres), approved prewashes, and underwater discharge.

Certificate: NLS Certificate / Certificate of Fitness.

Annex III — Harmful substances in packaged form

Applies to freight carried in containers, drums, tanks, and packages. The mandatory IMDG Code sets requirements for marking, labelling, packaging, segregation, stowage, and documentation.

Documentation: Dangerous Goods Manifest / Stowage Plan.

Annex IV — Sewage

Controls black water from toilets, urinals, and medical spaces. Requires certified Sewage Treatment Plants (STPs) or comminuting/disinfecting holding tanks, with discharge conditions based on distance from land.

Certificate: ISPP — International Sewage Pollution Prevention Certificate.

Annex V — Garbage

Discharge of all plastics is prohibited worldwide. Other domestic and operational waste is restricted. Food waste and non-harmful cargo residues may be discharged only under specified conditions and at specified distances.

Documents: Garbage Management Plan and Garbage Record Book.

Annex VI — Air pollution

Controls emissions from propulsion engines, auxiliaries, and incinerators: fuel sulphur (0.50% globally; 0.10% in ECAs), diesel NOx tiers, ozone-depleting substances, and energy efficiency (EEXI/CII).

Certificate: IAPP — International Air Pollution Prevention Certificate.

Operational discharge criteria depend directly on the ship's geographic position relative to land and water depth. Maritime law defines specific radial thresholds from the nearest baseline:

Figure 2: MARPOL distances and discharge conditionsCoastal profile with a schematic distance axis at 3, 12 and 50 nautical miles and separate conditional threshold lanes for ground and unground food, comminuted and disinfected sewage, untreated sewage and tanker cargo oil. Notes distinguish special areas, approved sewage treatment and cargo oil rate and total limits.Distance is a threshold — not permissionNearest land · schematic nautical-mile axis, not to scaleCOAST03 NM12 NM50 NMOffshoreFood · ground≥3 NM≤25 mm screen; en route; outside special areasFood · unground≥12 NMEn route; outside special areas; as far as practicableSewage · C&D¹>3 NMApproved comminution AND disinfection systemSewage · untreated>12 NMHolding-tank sewage: approved rate; en route ≥4 knCargo oil · tanker>50 NMOutside special areas / Arctic; en route; ODMCS + slopApproved STP: separate rule; no visible solids or water discoloration.Special areas: food ≥12 NM, ground ≤25 mm; passenger sewage rules differ.Cargo oil: ≤30 L/NM; total ≤1/30,000* of the cargo; all conditions apply.Plastics: no sea discharge. Mixtures follow the stricter rule.¹ C&D = comminuted & disinfected. * Pre-1980 tankers: 1/15,000.
Figure 2: MARPOL Nautical Distance & Permissible Discharge Matrix. Coastal zones impose graduated barriers: inshore waters (0–3 NM) prohibit all releases except certified STP effluent; 3–12 NM unlocks comminuted food (≤25 mm); 12–50 NM permits untreated sewage, non-ground food, and NLS tank washings (underwater ≥25 m depth); >50 NM is required for tanker cargo slops via ODMCS. Plastics remain universally banned everywhere.

3. Equipment, Discharge Limits & Records

MARPOL compliance has three parts:

  • Equipment: Approved separators, treatment plants, and other required hardware.
  • Discharge limits: Numerical limits such as 15 ppm, plus conditions including distance from land.
  • Records: Official logs that demonstrate compliance. Falsifying or failing to maintain them is a strict-liability criminal offence in most maritime jurisdictions.
Annex Regulated Stream Prescribed Hardware Permitted Effluent Criteria Official Record Book
Annex I Oily Bilge & Fuel Residues 15 ppm OWS, 15 ppm Bilge Alarm, Auto-stop 3-way valve, Sludge Tank ≤15 ppm oil in water, ship en route, no cargo mixture, outside Antarctic Oil Record Book Part I (Machinery) & Part II (Cargo/Ballast)
Annex II Noxious Liquid Chemicals in Bulk Deepwell stripping pumps (≤75 L), underwater discharge nozzle, P&A Manual Wake conc. ≤1 ppm (B) / ≤10 ppm (C), ≥12 NM, ≥25 m depth, ≥7 knots Cargo Record Book (NLS)
Annex III Packaged Dangerous Marine Pollutants Approved UN packaging, IMO hazard placards, weather-deck securing lashings Zero operational discharge; jettison permitted only to save ship/life Dangerous Goods Manifest / Stowage Plan
Annex IV Human Sanitary Effluent (Sewage) Type-approved STP (MEPC.227(64)), or comminuter/disinfection holding tank STP: TSS ≤35 mg/l, BOD5 ≤25 mg/l, coliform ≤100/100ml; Holding: ≥12 NM en route Sewage Log (Voluntary / Flag-mandated)
Annex V Shipboard Domestic & Cargo Garbage Food waste comminutor (≤25 mm mesh), incinerator, compaction press Food waste ≥3 NM (ground) or ≥12 NM (whole); ALL plastics banned Garbage Record Book Part I (All crew) & Part II (Cargo residues)
Annex VI Air Emissions (SOx, NOx, GHG) Exhaust Gas Cleaning System (Scrubber), Tier III SCR, Low-Sulphur lines Fuel S ≤0.50% (Global) / ≤0.10% (ECA); NOx limits curve N1/N2/N3 Ozone Depleting Log, Fuel Changeover Log, Bunker Delivery Notes (BDN)

Special areas and emission control areas

Special areas have stricter discharge rules because of their oceanographic conditions, ecological vulnerability, and shipping traffic.

Annex I — Oil: 10 special areas

Mediterranean Sea, Baltic Sea, Black Sea, Red Sea, "Gulfs" Area, Gulf of Aden, North-West European Waters, Antarctic Area, Oman Sea of the Arabian Sea, and Southern South African Waters.

Rule: Tanker cargo discharge is prohibited. Bilge water is permitted only if ≤15 ppm, en route, and processed through 15 ppm filtering equipment with automatic stop.

Annex V — Garbage: 8 special areas

Mediterranean Sea, Baltic Sea, Black Sea, Red Sea, "Gulfs" Area, North Sea, Antarctic Area, and Wider Caribbean Region.

Rule: Comminuted food waste (≤25 mm) is permitted only at ≥12 NM, rather than 3 NM. Discharge of domestic garbage, incinerator ash, cargo dunnage, and wash water additives is prohibited.

Annex VI — Emission control areas (ECAs)

Baltic Sea (SOx/NOx), North Sea (SOx/NOx), North American ECA (SOx/NOx/PM), United States Caribbean Sea ECA (SOx/NOx/PM), and Mediterranean Sea (SOx from May 2025).

Rule: The fuel sulphur cap falls from 0.50% to 0.10% m/m. Marine diesel engines installed on or after the designated dates must meet Tier III NOx limits, typically using SCR or LNG.

4. Certificates & Port State Control

A ship cannot legally trade internationally without carrying valid statutory certificates issued by or on behalf of its Flag Administration (frequently delegated to Recognised Organisations like DNV, Lloyd's Register, or ABS). All MARPOL certificates are harmonised under the Harmonised System of Survey and Certification (HSSC) with a 5-year maximum lifespan.

  • Certificate life: Maximum 5 years under HSSC.
  • Annual survey window: ±3 months.
  • BDN and Oil Record Book retention: 3 years.
  • Garbage Record Book retention: 2 years.

Port State Control (PSC) officers conduct shipboard audits following standard procedures established by regional agreements (Paris MoU, Tokyo MoU, US Coast Guard). An inspection follows an escalating protocol:

  1. Check documents. Review certificate validity and survey endorsements within the ±3 month window. Compare them with the Oil Record Book, Cargo Record Book, Garbage Record Book, and Bunker Delivery Notes.
  2. Inspect the ship. Check machinery spaces, steering flat, and deck. Look for OWS piping defects, unauthorized bypasses ("magic pipes"), oil stains on bilge valves, and poorly maintained garbage stations.
  3. Establish clear grounds. Missing certificates, incomplete tank soundings, missing piping flanges, fresh paint over bypasses, or crew unable to operate equipment justify a more detailed inspection.
  4. Test equipment. Demonstrate the 15 ppm OWS alarm and fail-safe diversion valve, check sewage aeration blowers, and collect fuel drip samples from the engine supply line.
  5. Rectify deficiencies or detain. Failures affecting seaworthiness or environmental safety—such as an inoperable OWS, falsified Oil Record Book, or defective incinerator—trigger a Code 30 Detention Notice. The ship cannot sail until the deficiencies are rectified.
1. INITIAL AUDIT • Check IOPP, ISPP, IAPP • Verify Annual Endorsements • Reconcile ORB, GRB, BDN CLEAR GROUNDS FOUND? NO: Satisfactory — Clean Inspection Report (Form A) SHIP CLEARED No Detainable Deficiencies YES 2. EXPANDED AUDIT • Test OWS 15 ppm alarm • Verify 3-way valve stop • Fuel sulphur drip sample ENVIRONMENTAL HAZARD / DEFECT? MINOR DEFECT CODE 17 / 16 DEFICIENCY • Rectify within 14 days or before departure • Vessel allowed to sail CRITICAL CODE 30 DETENTION • Ship CANNOT Sail • Flag State Notified • Class Re-survey Mandatory TOP DETENTION CAUSES: OWS 15 ppm bypass • Falsified Oil Record Book • Inoperable STP High fuel sulphur • Uncertified crew
Figure 3: Port State Control (PSC) Statutory Verification & Enforcement Escalation Flowchart. An inspection commences with an initial review of certificates and official logs (Step 1). If clear grounds are triggered by missing soundings, unapproved modifications, or crew unfamiliarity, the officer initiates an expanded audit with hands-on physical testing of 15 ppm valves and fuel sampling (Step 2). Critical safety and pollution failures trigger an immediate Code 30 Detention Notice prohibiting vessel departure.

Standards & sources referenced

  • MARPOL: International rules to prevent pollution from ships.
  • IMDG Code: Requirements for the safe carriage of dangerous goods in packaged form.
  • Conventions index
MEO question bank
MARPOL
Topic 1 of 8
  1. MARPOL 73/78: The Convention & Its Six Annexes
  2. MARPOL Annex I — Prevention of Pollution by Oil
  3. MARPOL Annex II — Noxious Liquid Substances in Bulk
  4. MARPOL Annex III — Harmful Substances in Packaged Form
  5. MARPOL Annex IV — Prevention of Pollution by Sewage from Ships
  6. MARPOL Annex V — Prevention of Pollution by Garbage from Ships
  7. MARPOL Annex VI — Air Pollution: SOx, NOx & Exhaust Gas Cleaning
  8. MARPOL Annex VI — Emission Reduction, EEDI, EEXI & CII
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