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UNCLOS overview for shipping

The United Nations Convention on the Law of the Sea (UNCLOS) is the principal instrument of public international law governing the world’s oceans, establishing the maritime zones through which commercial vessels transit, defining the rights and obligations of coastal states and flag states, and providing the jurisdictional foundation upon which instruments such as MARPOL, SOLAS, and the Ballast Water Management Convention derive their international application. Opened for signature on 10 December 1982 at Montego Bay, Jamaica, after nine years of negotiation, and entering into force on 16 November 1994, UNCLOS is sometimes called the ‘constitution of the oceans’. Its 320 articles and nine annexes define every zone from internal waters to the deep seabed, allocate enforcement jurisdiction among coastal, flag, and port states, codify the right of innocent passage through the territorial sea, establish transit passage through international straits, set out rules on piracy and hot pursuit, and create binding dispute-settlement mechanisms including the International Tribunal for the Law of the Sea (ITLOS). For shipowners, operators, and charterers, UNCLOS is not an abstract treaty - it determines which state may inspect a vessel, which rules that vessel must comply with in a given sea area, and which court has jurisdiction if a dispute arises. ShipCalculators.com provides tools aligned with the regulatory obligations that flow from this framework.

Contents

Background and history

Truman Proclamation and the 1958 conventions

The modern law of the sea emerged from a pair of unilateral acts that broke the 19th-century consensus holding the territorial sea to three nautical miles and the high seas to everything beyond. On 28 September 1945, United States President Harry Truman issued Presidential Proclamation 2667, asserting jurisdiction over the natural resources of the subsoil and seabed of the continental shelf adjacent to US coasts. The same day, Proclamation 2668 claimed a right to establish conservation zones in the high seas. These proclamations triggered cascading claims by other states, particularly Latin American nations, that challenged the three-mile rule and asserted 200-nautical-mile zones.

The International Law Commission responded by preparing draft articles that formed the basis for the first United Nations Conference on the Law of the Sea (UNCLOS I), held at Geneva in 1958. Four conventions emerged: the Convention on the Territorial Sea and the Contiguous Zone, the Convention on the High Seas, the Convention on the Continental Shelf, and the Convention on Fishing and Conservation of the Living Resources of the High Seas. A fifth protocol concerned compulsory dispute settlement. The 1958 conventions codified much of existing customary law but left the breadth of the territorial sea unresolved; a formula proposed at the 1960 UNCLOS II conference failed by one vote to achieve the required two-thirds majority, leaving the width question open for another two decades.

UNCLOS III and the Montego Bay Convention

Growing pressure from developing states, combined with the discovery of polymetallic nodules on the deep seabed and the prospect of their commercial exploitation, led the United Nations General Assembly in 1973 to convene the Third United Nations Conference on the Law of the Sea. Negotiations ran from 1973 to 1982 across 11 sessions, involving more than 150 delegations. The package deal approach - under which no article could be adopted in isolation - produced a convention that simultaneously expanded coastal state resource rights, codified navigational freedoms favoured by major maritime powers, and established a novel international regime for the deep seabed designated as the Common Heritage of Mankind.

The convention was opened for signature on 10 December 1982 in Montego Bay, Jamaica, and 117 states signed on the first day. One hundred and sixty-eight states and the European Union are parties as of 2026. The United States signed but did not ratify, primarily due to objections to Part XI governing deep seabed mining, though the 1994 Implementation Agreement modified Part XI to accommodate market-economy concerns. Despite non-ratification, the United States treats the navigational and overflight provisions of UNCLOS as reflective of customary international law and exercises rights under them.

UNCLOS entered into force on 16 November 1994, one year after the 60th ratification. The International Seabed Authority and ITLOS were both established in 1996, and the Seabed Disputes Chamber of ITLOS held its first session in that year.

Structure of the convention

The convention is divided into 17 parts and nine annexes. Part I covers general definitions. Parts II through VIII establish the maritime zones from the territorial sea through the high seas. Part IX addresses enclosed and semi-enclosed seas, and Part X covers the rights of land-locked states. Part XI governs the deep seabed Area and the ISA. Part XII establishes the environmental protection framework. Part XIII covers marine scientific research and Part XIV technology transfer. Part XV contains the dispute settlement provisions. The nine annexes deal with highly migratory species, the CLCS, ITLOS Statute, mediation and conciliation, arbitration, special arbitration, and other procedural matters.

The commercial shipping industry interacts with UNCLOS primarily through Parts II-V (maritime zones and navigational rights), Part VII (high seas, including flag state jurisdiction and piracy), Part XII (environmental obligations), Part XV (dispute resolution), and Annex VI (ITLOS Statute). The convention’s language on navigational rights is generally precise, while the language on environmental protection and the genuine link is intentionally flexible, leaving content to be filled by IMO conventions and subsequent state practice.

Maritime zones

UNCLOS establishes a layered set of maritime zones measured from baselines drawn along the coast. Each zone carries a distinct balance of coastal state rights and navigational freedoms.

Baselines

Normal baselines follow the low-water mark as shown on large-scale charts officially recognised by the coastal state (Article 5). Where the coastline is deeply indented, unstable, or fringed with islands, straight baselines may be drawn joining appropriate points (Article 7), provided the general direction of the coast is followed and the sea areas enclosed are sufficiently linked to the land domain. Archipelagic states - those constituted wholly by one or more archipelagos - may draw archipelagic baselines joining the outermost points of the outermost islands (Article 47), enclosing archipelagic waters. The Philippines and Indonesia are the two most significant shipping-relevant examples.

Internal waters

Waters on the landward side of the baseline constitute internal waters (Article 8). The coastal state exercises full sovereignty over internal waters as over its land territory. Foreign vessels have no right of innocent passage unless the baseline was drawn across a previously non-enclosed bay or strait. Ports fall within internal waters; the decision whether to admit a foreign vessel to a port is a matter of sovereign discretion in peacetime, though port access rights are frequently conferred by bilateral agreements and customary law prevents arbitrary exclusion for non-safety reasons.

Territorial sea

The territorial sea extends up to 12 nautical miles from the baseline (Article 3). Coastal state sovereignty over the territorial sea is complete, encompassing the water column, seabed, subsoil, and airspace, subject only to the right of innocent passage for foreign ships. The breadth of 12 nautical miles, contested since 1958, was definitively settled by UNCLOS and is now universally accepted as the maximum, though states may claim a narrower belt.

Right of innocent passage

Article 17 grants ships of all states the right of innocent passage through the territorial sea. Passage is innocent as long as it is not prejudicial to the peace, good order, or security of the coastal state (Article 19). Article 19(2) provides an exhaustive list of activities that render passage non-innocent, including weapons exercises, intelligence gathering, launching or landing of aircraft or military devices, loading or unloading contrary to coastal state customs, fisheries activities, research or survey activities, and acts of wilful and serious pollution.

For merchant shipping, the critical distinction is between transit and the prohibited activities in Article 19(2). A vessel proceeding continuously and expeditiously through the territorial sea while complying with MARPOL, SOLAS, and navigational safety rules is in innocent passage. Coastal states may not impose conditions that have the practical effect of denying or impairing innocent passage (Article 24), and they may not levy charges solely for passage (Article 26). They may, however, designate sea lanes and traffic separation schemes (Article 22), and vessels carrying nuclear materials or hazardous cargoes must carry the relevant international documents and comply with special precautionary measures.

Coastal states may temporarily suspend innocent passage in specified areas of the territorial sea for security reasons (Article 25(3)). Such suspensions must be announced and must not discriminate in form or fact against vessels of any state.

Contiguous zone

The contiguous zone extends up to 24 nautical miles from the baseline (Article 33). Within this zone the coastal state may exercise the control necessary to prevent or punish infringement of its customs, fiscal, immigration, or sanitary laws and regulations committed in its territory or territorial sea. The contiguous zone carries no general navigational restrictions; its significance for commercial shipping lies primarily in customs enforcement and the right of hot pursuit that begins there.

Exclusive economic zone

The exclusive economic zone (EEZ) extends up to 200 nautical miles from the baseline (Articles 55-75). The EEZ is the most economically significant zone created by UNCLOS. The coastal state holds sovereign rights for the purpose of exploring, exploiting, conserving, and managing living and non-living natural resources of the water column, seabed, and subsoil. It also has jurisdiction over artificial islands, installations, and structures; marine scientific research; and the protection and preservation of the marine environment.

All other states retain the freedoms of navigation, overflight, laying of submarine cables and pipelines, and other internationally lawful uses of the sea within the EEZ. Commercial vessels therefore transit EEZs under the same practical freedom as the high seas with respect to navigation, though the coastal state’s environmental jurisdiction - particularly regarding operational discharges - is enhanced compared with the high seas.

The concept of the EEZ resolved the competing 200-mile claims of the 1960s and 1970s by creating a zone of resource rights without fully extending sovereignty. Approximately 36% of the world’s ocean area falls within national EEZs, and virtually all commercially significant fisheries and offshore hydrocarbon resources lie within them.

Continental shelf

The continental shelf comprises the seabed and subsoil of the submarine areas extending beyond the territorial sea throughout the natural prolongation of the land territory (Article 76). The default outer limit is 200 nautical miles from the baseline, coextensive with the EEZ, regardless of geological conditions. Where the natural prolongation extends beyond 200 miles, the outer limit may reach up to 350 nautical miles from the baseline, or 100 nautical miles from the 2,500-metre isobath - whichever is further from the coast.

Extended continental shelf claims must be submitted to the Commission on the Limits of the Continental Shelf (CLCS), a body of 21 geoscientists established under Annex II of UNCLOS. The CLCS reviews submissions and makes recommendations; the outer limit established on the basis of those recommendations is final and binding. Commercially, extended continental shelf rights affect offshore drilling operations, subsea pipeline routing, and the jurisdictional reach of the coastal state over hydrocarbon extraction.

High seas

The high seas comprise all parts of the sea not included in the EEZ, territorial sea, internal waters, or archipelagic waters (Article 86). The freedom of the high seas - navigation, overflight, laying cables and pipelines, fishing, scientific research, and construction of artificial islands - is codified in Article 87. No state may validly subject any part of the high seas to its sovereignty. On the high seas, jurisdiction over a vessel is exercised exclusively by the flag state, subject to specified exceptions including piracy, slave trade, unauthorised broadcasting, stateless vessels, and vessels exercising the right of hot pursuit.

Article 94 duties

Article 91 of UNCLOS provides that every state has the right to grant its nationality to ships; ships have the nationality of the state whose flag they are entitled to fly. Article 91 also requires a genuine link between the state and the ship, though UNCLOS itself does not define what constitutes such a link, an ambiguity that has generated persistent controversy.

Article 94 is the operational core of flag state responsibility. It requires every state to effectively exercise its jurisdiction and control in administrative, technical, and social matters over ships flying its flag. Specific obligations include: maintaining a register of ships, assuming jurisdiction over the ship and its master, officers, and crew in administrative, technical, and social matters; ensuring compliance with internationally accepted regulations on the design, construction, equipment, and seaworthiness of ships; and taking measures to prevent collision, pollution, and overloading.

The phrase “internationally accepted regulations” in Article 94 is the treaty bridge connecting UNCLOS to IMO conventions. Flag states that ratify SOLAS, MARPOL, STCW, and the MLC 2006 implement their Article 94 duties through those instruments. A flag state that issues trading certificates to a vessel without verifying compliance with these conventions is in breach of Article 94.

The flag state IMSAS audit calculator reflects the IMO Member State Audit Scheme, which is the primary mechanism by which the international community evaluates whether flag states meet their Article 94 obligations. Audit findings are transmitted to the IMO Council; persistent non-compliance may lead to a flag being listed as a “flag of non-compliance” in port state control MOU annual reports.

The genuine link requirement of Article 91 was intended to prevent states from registering ships purely for revenue without exercising effective control. In practice, open registries - Panama, Liberia, Marshall Islands, Bahamas, and others - have interpreted the requirement loosely, treating payment of registration fees as sufficient. By fleet size, open-registry flags collectively account for a substantial majority of world merchant tonnage.

The International Court of Justice’s advisory opinion in the IMCO case (1960) and the International Tribunal’s decision in the M/V Saiga case (1997) both declined to hold that the absence of an effective link invalidated a flag nationality for purposes of diplomatic protection, though the Tribunal acknowledged the tension. The Liberia flag details calculator and the Panama flag details calculator reflect the regulatory frameworks these two major open registries have established.

Critics of flags of convenience argue that genuine-link looseness enables substandard shipping: labour standards below MLC 2006 requirements, maintenance below SOLAS standards, and environmental compliance below MARPOL requirements. Defenders point out that major open registries have invested in their regulatory infrastructure and their detention rates in port state control MOU regimes are often lower than those of some traditional maritime nations.

Straits used for international navigation

Transit passage

When a strait is used for international navigation between one part of the high seas or EEZ and another part of the high seas or EEZ, ships and aircraft of all states enjoy the right of transit passage (Article 38). Transit passage is the right of continuous and expeditious transit in the normal mode of operation; it differs from innocent passage in that it cannot be suspended by the coastal state and it extends to aircraft and submarines (submarines may transit submerged). The coastal state may designate sea lanes and prescribe traffic separation schemes in conformity with international regulations (Article 41), and may enforce laws relating to safety of navigation and pollution prevention, but cannot restrict or charge for transit.

The four straits of greatest commercial significance are:

Strait of Hormuz: Connecting the Persian Gulf to the Gulf of Oman, the Strait of Hormuz carries tanker traffic representing a large fraction of world seaborne oil exports. Iran and Oman are the coastal states; Iran has periodically threatened to close the Strait, a threat that would constitute a violation of UNCLOS transit passage rights. The minimum width at the navigable channel is approximately 33 kilometres. No alternative route for supertankers exists.

Bab el-Mandeb: At the southern entrance to the Red Sea, Bab el-Mandeb links the Indian Ocean to the Suez Canal route. Yemeni coastal state authority on the eastern shore has been disrupted by ongoing conflict since 2015; the instability affecting transit through this strait led to a significant diversion of container traffic to the Cape of Good Hope route from late 2023 onward, substantially increasing voyage distances and fuel consumption.

Strait of Malacca: The main commercial artery between the Indian Ocean and the South China Sea, transited by a large share of world container trade, much of East Asia’s oil imports, and bulk commodity traffic. Indonesia, Malaysia, and Singapore are the coastal states, and the three have cooperated on coordinated patrols since 2004 under the Malacca Strait Patrols initiative. The passage planning through this strait must account for traffic separation schemes established under Article 41.

English Channel (Strait of Dover): The narrowest point of this key European waterway is approximately 33 kilometres. France and the United Kingdom are the coastal states. The deep-water route for vessels over certain draughts runs through the traffic separation scheme operated under IMO authority; the Dover Strait Traffic Separation Scheme is one of the busiest in the world.

Archipelagic sea lanes passage

Archipelagic sea lanes passage (Articles 53-54) applies within the archipelagic waters of archipelagic states. Ships and aircraft of all states have the right of continuous, expeditious, and unobstructed transit through sea lanes and air routes designated by the archipelagic state. Where no sea lanes are designated, the right extends to normal passage routes.

For commercial shipping, the archipelagic waters of Indonesia and the Philippines are the principal application areas. Indonesian designated sea lanes cover the principal through routes connecting the South China Sea and the Pacific Ocean to the Indian Ocean, including the Sunda Strait, Lombok Strait, and Ombai-Wetar passage.

Port state control

Port state jurisdiction under UNCLOS

A port state has greater enforcement jurisdiction than a coastal state in the EEZ because the vessel has voluntarily entered the state’s territory. Articles 218, 219, and 220 of UNCLOS define port state jurisdiction over pollution violations:

  • Article 218 permits a port state to investigate and institute proceedings in respect of any discharge violation that has occurred on the high seas, in the EEZ of another state, or in the territorial sea - if the discharge violates applicable international rules - when the foreign vessel is voluntarily in port.
  • Article 219 requires a port state to prevent the sailing of a vessel that does not meet seaworthiness standards, detaining the vessel until it proceeds to the nearest appropriate repair yard.
  • Article 220 addresses coastal state enforcement for EEZ violations, allowing detention when there is clear ground to believe a vessel committed a violation causing or threatening major damage.

These provisions created the legal basis for the regional memoranda of understanding (MoUs) on port state control - Paris MOU, Tokyo MOU, Black Sea MOU, and others - which coordinate inspections among member states. The PSC targeting factor calculator reflects the risk-based targeting methodology used by these regimes, while the Paris MOU detention probability calculator models the statistical likelihood of a vessel being detained.

Article 228 and the primacy of flag state proceedings

Article 228 limits the ability of coastal and port states to institute proceedings for offshore violations once the flag state has commenced its own proceedings within six months of the initial institution. If the flag state has imposed a penalty, the port state or coastal state proceedings must be suspended and ultimately discontinued, except for violations in the territorial sea or cases involving major damage. This provision was a concession to flag state sovereignty during UNCLOS III negotiations but has been criticised as weakening enforcement against persistent violators.

Detention, bonding, and prompt release

When a coastal or port state detains a vessel under Articles 219 or 220, UNCLOS Article 292 provides the detained vessel’s flag state with the right to apply to ITLOS for prompt release upon posting a reasonable bond or other financial security. The application may be made even while domestic proceedings are pending in the detaining state, provided the detaining state has not applied to ITLOS for release itself. ITLOS must act with all practical speed in determining whether to order release.

Prompt release has been invoked in numerous cases involving vessels detained for alleged fisheries violations, pollution offences, and customs infractions. ITLOS has consistently held that the bond must bear a reasonable relationship to the gravity of the alleged offence and the value of the detained vessel, and must not be set at a level that amounts to confiscation in advance of judgment. For shipowners and P&I clubs, the prompt release mechanism provides a critical safeguard against indefinite detention pending the outcome of coastal state proceedings that may take years to conclude. The bond amount determined by ITLOS is typically assessed against the value of the vessel, the cargo value, and the gravity of the alleged violation, with ITLOS retaining discretion to reduce amounts it considers excessive.

Marine pollution - Part XII

The framework approach

Part XII of UNCLOS (Articles 192-237) establishes a comprehensive framework for the protection and preservation of the marine environment. Article 192 states that states have the obligation to protect and preserve the marine environment. Article 194 requires states to take all measures necessary to prevent, reduce, and control pollution from any source, including ships.

The critical drafting choice in Part XII was the framework approach: rather than specifying emission standards or equipment requirements, UNCLOS requires states to give effect to “generally accepted international rules and standards” established through “the competent international organization” - which in practice means the IMO and its instruments. Article 211 is the principal provision for vessel-source pollution, requiring states to establish international rules and standards through the competent international organisation, and to adopt laws and regulations for vessels flying their flag that at least equal those international rules.

The effect is that MARPOL standards - Annex I for oil, Annex II for noxious liquid substances, Annex IV for sewage, Annex V for garbage, Annex VI for air emissions - become the content of the “generally accepted international rules” referred to in Article 211, and are thus binding on flag states through their UNCLOS Article 94 duties even in respect of non-MARPOL parties, at least in customary international law terms. The IMO MARPOL overview calculator maps the Annex VI requirements that flow from this chain of authority.

Special areas and emission control areas

Article 211(6) permits coastal states, when international standards are inadequate to meet their particular environmental characteristics, to seek through the IMO the adoption of additional pollution prevention measures for a defined sea area. This mechanism was used to establish Special Areas under MARPOL Annexes I, II, and V, and - adapted into the MARPOL framework directly - to establish Emission Control Areas (ECAs) under Annex VI, where the 0.10% sulphur cap and Tier III NOx standards apply.

The IMO 2020 sulphur cap reduced the global sulphur limit to 0.50% from 1 January 2020, while the ECA sulphur limit of 0.10% had been in force since 2015. Vessels operating within ECAs must use marine gas oil or equivalent-sulphur compliant fuel, operate approved exhaust gas cleaning systems, or use alternative fuels such as LNG.

CII, EEDI, and EEXI: emissions efficiency

The carbon intensity and energy efficiency measures adopted under MARPOL Annex VI - the Energy Efficiency Design Index (EEDI), the Energy Efficiency Existing Ship Index (EEXI), and the Carbon Intensity Indicator (CII) - are the IMO’s primary instruments for reducing CO2 from shipping. These instruments derive their international application from the UNCLOS-MARPOL chain described above.

The EEDI Attained calculator and EEDI Required calculator quantify the design-phase efficiency requirement for new ships. The EEXI Attained calculator and EEXI Required calculator apply to ships already in service. The CII Attained calculator and CII Required calculator implement the operational carbon intensity rating system, further analysed in the MARPOL Annex VI CII Rating calculator. All these tools operate within the legal framework that UNCLOS establishes for flag state obligations. Further background is available in the what is CII, what is EEXI, and what is EEDI articles.

Ballast water and the BWM Convention

The Ballast Water Management Convention entered into force in September 2017, requiring ships to manage their ballast water to prevent the transfer of invasive aquatic species. The BWM Convention discharge location checker and the IMO BWMC overview reflect obligations that flow ultimately from Part XII of UNCLOS. The IMO DCS annual report tool covers the data collection system under MARPOL Annex VI, another Part XII derivative instrument.

Article 234 and ice-covered areas

Article 234 of UNCLOS grants coastal states the right to adopt and enforce non-discriminatory laws and regulations for the prevention, reduction, and control of marine pollution from vessels in ice-covered areas within their EEZ, provided that environmental conditions make navigation particularly hazardous and pollution could cause major harm to or irreversible disturbance of the ecological balance. The article is the treaty basis for Canada’s Arctic Waters Pollution Prevention Act and Russia’s Northern Sea Route regulations, which impose standards more stringent than baseline MARPOL requirements - including requirements for vessel class, ice-strengthening, navigation equipment, and mandatory pilotage or icebreaker escort.

The Polar Code, which entered into force on 1 January 2017, updated the SOLAS and MARPOL frameworks for polar operations, introducing a mandatory ship category and polar water operational manual. The Polar Code does not supersede Article 234; Canada and Russia retain the authority to require standards beyond Polar Code minimums within their EEZ ice-covered areas. For commercial vessels transiting the Northern Sea Route or Northwest Passage - routes whose commercial attractiveness increases as Arctic sea ice extent declines - compliance with both the Polar Code and the applicable national legislation is required.

Slow steaming and voyage optimisation

The intersection of UNCLOS and MARPOL Annex VI creates a regime in which commercial operators must balance speed, fuel consumption, emissions intensity, and CII rating. Slow steaming and CII analyses how reducing service speed affects the attained CII, with slower speeds typically improving the carbon intensity ratio. This optimisation occurs within the navigational freedom framework that UNCLOS establishes: on the high seas and in EEZs, no coastal state may restrict vessel speed for commercial reasons, but flag states and charterers manage speed through operational instructions and charter party clauses. The IMO’s goal-based regulatory approach - setting emission intensity targets without prescribing the means of compliance - reflects the UNCLOS principle that flag states determine the means by which international standards are met aboard their vessels.

Piracy and armed robbery

Articles 100-107: universal jurisdiction on the high seas

UNCLOS Articles 100-107 codify the law of piracy. Article 101 defines piracy as: (a) any illegal acts of violence or detention, or any act of depredation, committed for private ends by the crew or passengers of a private ship or aircraft against another ship or aircraft or persons or property on board, on the high seas or in a place outside the jurisdiction of any state; or (b) any act of voluntary participation in the operation of such a ship or aircraft; or (c) any act of inciting or facilitating such acts.

Three elements are essential: the acts must be for private ends (distinguishing piracy from politically motivated acts), they must involve two vessels (the “two-ship” requirement - a mutiny is therefore not piracy under UNCLOS), and they must occur on the high seas or in a place outside any state’s jurisdiction. This last requirement is significant: attacks within a state’s territorial sea are not piracy under UNCLOS but constitute armed robbery at sea, which falls under the coastal state’s criminal jurisdiction.

Article 105 grants every state the right to seize a pirate ship on the high seas and to arrest the persons and seize the property on board, with the courts of the seizing state empowered to determine penalties. This is one of the few explicit grants of universal jurisdiction in conventional international law. Article 107 restricts seizure authority to warships, military aircraft, and other government ships or aircraft clearly marked and identifiable as such.

The Piracy BMP5 Transit Speed calculator and the Gulf of Guinea piracy precautions calculator reflect the operational guidance of Best Management Practices (BMP5) issued by industry bodies, which in turn implement the flag state obligations derived from Articles 100-107. Piracy in the Gulf of Aden and Somalia peaked between 2008 and 2012 and has been reduced substantially by naval presence, BMP implementation, and armed security teams; piracy in the Gulf of Guinea has persisted at a significant level.

Armed robbery in territorial waters

The distinction between UNCLOS piracy (high seas only) and armed robbery at sea (territorial waters) has practical consequences. A warship cannot exercise the UNCLOS seizure authority of Article 105 within another state’s territorial waters without that state’s consent; doing so would violate the sovereignty protected by Article 2. The regional anti-piracy cooperation framework coordinated by the Regional Cooperation Agreement on Combating Piracy and Armed Robbery against Ships in Asia (ReCAAP, established 2006) addresses this gap by creating information-sharing and cooperative response mechanisms among member states.

Separately, UN Security Council resolutions - including UNSC Resolution 1816 (2008) and subsequent resolutions adopted during the Somali piracy crisis - authorised states and regional organisations to enter Somali territorial and internal waters to repress piracy, constituting an exception to the general rule that UNCLOS Article 105 jurisdiction is confined to the high seas. These resolutions operated under Chapter VII of the UN Charter and were time-limited; they do not establish a general precedent that Article 105 jurisdiction can be extended by Security Council resolution, but they demonstrate that the international community can adapt the UNCLOS piracy framework when coastal state governance has collapsed. The IMO Djibouti Code of Conduct (2009, revised as the Jeddah Amendment 2017) provides a regional treaty framework for information sharing and capacity building in the Red Sea, Gulf of Aden, Indian Ocean, and Red Sea area.

Hot pursuit

Article 111 of UNCLOS codifies the right of hot pursuit: a coastal state may pursue a foreign ship beyond the outer limit of its jurisdictional zones if there are good reasons to believe that the ship has violated the laws and regulations of that state while in the state’s internal waters, archipelagic waters, territorial sea, or contiguous zone. Hot pursuit must begin while the foreign vessel is still within those zones and must be continuous; it ends when the pursued vessel enters the territorial sea of its own state or a third state. A signal to stop must be given by a visual or auditory signal recognisable at a distance before pursuit begins. If pursuit is launched from the contiguous zone, it is only permitted for violations of the rights for which the zone was established.

The right of hot pursuit was confirmed in the M/V Saiga case before ITLOS in 1997, where the tribunal found that Guinea’s hot pursuit of the Saiga was unlawful because the vessel had not been in Guinea’s EEZ when the alleged violation occurred and the conditions of Article 111 had not been met. The tribunal further noted that the signal given by the Guinean patrol vessel was a radio communication rather than the “visual or auditory signal” required by Article 111(4), independently rendering the pursuit unlawful. The case remains the leading authority on what constitutes valid commencement of hot pursuit and is routinely cited in flag state diplomatic protection claims when vessels are arrested by coastal states in disputed circumstances.

Dispute settlement

Article 287 mechanisms

Part XV of UNCLOS (Articles 279-299) establishes a compulsory, binding dispute settlement system - a feature unprecedented in a multilateral convention of this scope at the time of its adoption. Article 287 allows states to choose one or more of four forums for binding dispute settlement: ITLOS, the International Court of Justice (ICJ), arbitration under Annex VII, or special arbitration under Annex VIII for disputes relating to fisheries, navigation and overflight, marine scientific research, or marine pollution. If parties to a dispute have not made a compatible choice, or have made no choice, Annex VII arbitration applies by default.

International Tribunal for the Law of the Sea

ITLOS, based in Hamburg, was established by Annex VI of UNCLOS and began operating in 1996. It consists of 21 independent judges elected by state parties. The full tribunal has jurisdiction over any dispute arising under UNCLOS. Chambers exist for seabed disputes, summary procedure, and specific categories. ITLOS also has authority under Article 292 to order the prompt release of detained vessels and their crews upon the posting of bond - a provision of particular importance to commercial shipping when vessels are arrested by coastal states.

Prompt release cases have constituted a significant portion of ITLOS’s docket. In the M/V Saiga (No. 2) case (1999), ITLOS awarded damages to Saint Vincent and the Grenadines after finding that Guinea had unlawfully used force during the arrest, had not met the conditions for hot pursuit, and had detained the vessel and crew in violation of UNCLOS. The award addressed MFN treatment in bond amounts and the appropriate use of force in maritime law enforcement - principles directly applicable to flag state protection of commercial vessels.

The South China Sea Arbitration

The 2016 award by a Permanent Court of Arbitration Annex VII tribunal in the Philippines v China arbitration (the South China Sea Arbitration) is the most consequential UNCLOS dispute affecting commercial shipping in the Indo-Pacific. The tribunal found that China’s historic rights claims within the nine-dash line were inconsistent with UNCLOS, that Mischief Reef and several other features are low-tide elevations generating no maritime entitlements, and that China had violated its obligations under UNCLOS by interfering with Philippine fishing and hydrocarbon activities. China disputed the tribunal’s jurisdiction and declined to participate. The award has not been enforced but has shaped the diplomatic and legal framing of navigational freedom claims in the South China Sea, through which a large share of world container trade passes.

Enrica Lexie (Italy v India)

The 2020 ITLOS Order in Enrica Lexie illustrates the tension between flag state and coastal state jurisdiction in the EEZ. In February 2012, two Italian marines aboard the tanker Enrica Lexie shot and killed two Indian fishermen in India’s EEZ. Italy and India disputed jurisdiction. The case was eventually referred to Annex VII arbitration, which in 2020 awarded jurisdiction to Italy on the basis that the marines were entitled to immunity as state officials exercising official functions. India was ordered to cease criminal proceedings and Italy to provide reparations. The case highlighted the difficulty of applying Articles 97 and 111 to incidents involving official personnel aboard commercial vessels.

The 1994 Part XI Implementation Agreement and deep seabed mining

Part XI of UNCLOS (Articles 133-191) establishes the international regime for the deep seabed beyond national jurisdiction - the “Area” - designated as the Common Heritage of Mankind. The International Seabed Authority (ISA), based in Kingston, Jamaica, was established to organise and control all mineral-related activities in the Area. Commercial seabed mining of polymetallic nodules, polymetallic sulphides, and cobalt-rich ferromanganese crusts requires an ISA contract.

The United States’ objections to Part XI - particularly to technology transfer requirements, production controls, and the institutional structure of the parallel mining system - led to the 1994 Implementation Agreement, which substantially modified Part XI. The ISA has issued exploration contracts to contractors from multiple states; no commercial-scale extraction was underway as of 2026. The environmental rules for mining operations in the Area are under development through the ISA’s ongoing Mining Code process.

For commercial shipping, the relevance of the ISA regime lies primarily in the prospect of future bulk mineral traffic from mid-ocean mining operations, which would require new port infrastructure and specialised vessel types capable of handling wet and dry nodule cargo, and in the environmental standards applicable to mining support vessels operating in the Area.

International linkages

BBNJ Agreement

The Agreement under the United Nations Convention on the Law of the Sea on the Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction (the BBNJ Agreement), adopted on 19 June 2023 and opened for signature on 20 September 2023, addresses four main areas: marine genetic resources, area-based management tools including marine protected areas, environmental impact assessments, and capacity building and technology transfer. The BBNJ Agreement is an implementing agreement under UNCLOS, operating within the UNCLOS framework rather than as a standalone instrument.

For commercial shipping, the practical implication of BBNJ lies primarily in the potential designation of marine protected areas on the high seas that could affect vessel routing. Area-based management tools under BBNJ require parties to consider impacts on shipping and to consult with the IMO as the competent organisation for vessel-related matters. The BBNJ Agreement had not yet entered into force as of April 2026.

UN Fish Stocks Agreement

The 1995 Agreement for the Implementation of the Provisions of the United Nations Convention on the Law of the Sea relating to the Conservation and Management of Straddling Fish Stocks and Highly Migratory Fish Stocks (UNFSA) supplements UNCLOS by establishing binding standards for regional fisheries management organisations (RFMOs) and imposing on flag states specific duties regarding the high-seas fishing activities of vessels flying their flags. While directly concerned with fisheries rather than commercial shipping, UNFSA reinforces the principle that flag state jurisdiction carries substantive obligations - a principle that port state control of merchant vessels under UNCLOS draws upon.

SOLAS, MARPOL, BWM, STCW, and MLC

The major IMO conventions and the MLC 2006 derive their character as universally applicable international standards partly from their status as “generally accepted international rules” referenced in UNCLOS Articles 94 and 211. A coastal or port state invoking UNCLOS enforcement jurisdiction over a foreign vessel in its EEZ or port grounds that enforcement on Article 211(5) (for coastal state EEZ enforcement), Article 218 (for port state enforcement of discharge violations), or Article 219 (for seaworthiness), with the substantive standards provided by MARPOL, SOLAS, or STCW.

This chain of authority is why compliance with these IMO conventions matters even for vessels calling at ports of non-party states or transiting the EEZ of non-party states: UNCLOS binds flag states to these standards independently of whether their ships visit only party-state ports. The SOLAS convention overview, MARPOL convention overview, STCW convention overview, and MLC 2006 overview each elaborate the specific obligations flowing from these instruments.

The ISM Code, formally the International Safety Management Code adopted under SOLAS Chapter IX, operationalises flag state safety management obligations. The ISPS Code implements post-2001 maritime security requirements. The Polar Code establishes mandatory safety and environmental requirements for ships operating in Arctic and Antarctic waters - areas where coastal state jurisdiction under UNCLOS Article 234 gives Canada and Russia enhanced authority to prescribe and enforce pollution prevention measures applicable to ice-covered areas within their EEZ.

Civil liability conventions

The International Convention on Civil Liability for Oil Pollution Damage (CLC) and the Bunker Convention 2001 operate within the jurisdictional framework UNCLOS establishes. The IMO CLC liability calculator and the Bunker Convention liability calculator reflect limits that apply when a vessel causes pollution damage in the territorial sea or EEZ of a state party - areas where the coastal state’s enforcement jurisdiction under UNCLOS Articles 220 and 228 intersects with the civil liability regime.

EU regulatory extensions

The European Union has enacted regulations extending flag state obligations into the ETS and FuelEU Maritime domains. The EU ETS annual allowance cost calculator and the FuelEU Maritime penalty calculator reflect obligations that apply to vessels calling at EU ports - port state jurisdiction exercised consistently with Articles 218 and 25 of UNCLOS. The EU ETS for shipping and FuelEU Maritime explained articles provide detailed analysis.

Maritime boundary delimitation

Equidistance and special circumstances

UNCLOS Articles 15 (territorial sea), 74 (EEZ), and 83 (continental shelf) prescribe delimitation of overlapping maritime claims between states with opposite or adjacent coasts. Article 15 establishes the equidistance principle for the territorial sea, subject to historic title or special circumstances. Articles 74 and 83 do not specify a method but require delimitation to be “effected by agreement on the basis of international law in order to achieve an equitable solution.”

International case law has developed a three-stage methodology for EEZ and continental shelf delimitation: first, construct a provisional equidistance line; second, consider whether relevant circumstances require adjustment; third, verify that the result is not disproportionate to the length of the parties’ relevant coastlines. The presence of islands, the concavity of a coastline, and the location of natural resources are typical factors considered in adjustment.

Commercial shipping interests arise in boundary disputes because unresolved or disputed boundaries create uncertainty about which state’s port state control regime applies, which state’s mandatory routing measures govern, and under which flag-state/coastal-state allocation enforcement jurisdiction falls. The South China Sea remains the most commercially significant example of unresolved maritime boundary claims, with overlapping EEZ claims among China, Vietnam, the Philippines, Malaysia, and Brunei affecting vessel routing, offshore operations, and the exercise of fisheries jurisdiction.

Provisional arrangements and joint development zones

Where maritime boundaries have not been definitively delimited, UNCLOS Articles 74(3) and 83(3) require states to make every effort to enter into provisional arrangements of a practical nature and not to jeopardise or hamper the reaching of a final agreement. In practice, overlapping EEZ and continental shelf claims are sometimes addressed through joint development zones, under which the resources of a disputed area are exploited on a shared basis pending final delimitation. The Timor Sea Treaty (2002) and subsequent instruments between Australia and Timor-Leste represent one model; the Malaysia-Thailand Joint Development Area in the Gulf of Thailand another.

For vessels serving offshore operations in joint development zones, the practical question of which state’s maritime labour, safety, and environmental law applies can be complex. The relevant treaty typically allocates administrative jurisdiction to one state or establishes a joint authority with combined competence. Classification society surveys and flag state inspections remain the primary compliance mechanisms for the vessel itself, irrespective of the resource-sharing arrangement for the underlying hydrocarbon or mineral asset.

Modern practice and current developments

IMO Member State Audit Scheme

The IMO Member State Audit Scheme (IMSAS), made mandatory in 2016 through amendments to SOLAS, MARPOL, STCW, and other instruments, establishes a standardised framework for auditing states’ compliance with their flag, port, and coastal state obligations under IMO conventions. IMSAS audits are conducted against the IMO Instruments Implementation Code (III Code), adopted by Assembly Resolution A.1070(28). The flag state IMSAS audit tool assists in mapping a flag state’s performance against the III Code criteria.

Audit results feed into port state control MOU databases. Port state control officers may assign higher targeting priority to vessels flying the flag of a state whose IMSAS audit disclosed significant deficiencies in its oversight framework. This creates a market feedback mechanism: flag states that fail to meet Article 94 obligations face a commercial disadvantage for their registered fleet.

Port state control MOU regimes

Nine regional MoUs now cover virtually all significant port states: Paris MOU (Europe and North Atlantic), Tokyo MOU (Asia-Pacific), Indian Ocean MOU, Abuja MOU (West Africa), Acuerdo de Viña del Mar (Latin America), Caribbean MOU, Mediterranean MOU (Memorandum d’Entente), Riyadh MOU (Gulf), and Black Sea MOU. Each MOU operates a database of inspection records and maintains a list of banned vessels with persistent records of detention. The port state control overview article describes these regimes in detail.

The Paris MOU’s annual report on port state control performance, published each year, provides a statistical breakdown of deficiencies by convention, by flag, and by vessel type. Common categories of deficiency consistently include fire safety, life-saving appliances, ISM Code compliance, and MARPOL documentation - all categories rooted in the “internationally accepted regulations” that flag states must enforce under Article 94 of UNCLOS. The Paris MOU’s “Black List” identifies flags whose vessels exceed detention threshold rates; vessels flying listed flags receive enhanced targeting. The Paris MOU Concentrated Inspection Campaign (CIC) focuses each year on a specific convention or set of requirements, effectively deploying coordinated port state enforcement as a proxy for flag state performance.

Vessel traffic services and mandatory reporting

Coastal states may establish vessel traffic services (VTS) and mandatory ship reporting systems in the territorial sea and, with IMO approval, in the EEZ. SOLAS Chapter V, which operates within the UNCLOS framework, requires ships to comply with mandatory reporting in areas where such systems have been established and approved by the IMO. The Torres Strait in Australia, the Great Belt in Denmark, and the approaches to major ports worldwide operate VTS systems whose authority derives from coastal state jurisdiction over the territorial sea combined with SOLAS-mandated reporting obligations.

Mandatory ship reporting also operates under the International Convention for the Safety of Life at Sea for vessels in certain sea areas. These reporting requirements, while operationally a matter of SOLAS and IMO navigation safety rules, are grounded in the coastal state’s Article 22 right to designate sea lanes and prescribe traffic separation schemes, and in the flag state’s Article 94 duty to ensure masters are equipped with current charts and navigational safety instructions.

ITLOS advisory jurisdiction

ITLOS has issued advisory opinions on request from the ISA Seabed Disputes Chamber and - following a 2022 request from the Commission of Small Island States on Climate Change and International Law (COSIS) - on the obligations of states under UNCLOS with respect to climate change. The ITLOS advisory opinion on climate obligations, delivered in May 2024, held that CO2 constitutes a “pollutant” for purposes of UNCLOS Part XII, imposing obligations on flag and coastal states to reduce CO2 emissions that go beyond what the current MARPOL Annex VI framework alone requires. The opinion does not bind states as a matter of treaty law but is expected to influence future IMO negotiations and potentially domestic climate litigation involving shipping.

The BBNJ entry-into-force timeline

As of April 2026, the BBNJ Agreement was approaching the 60-ratification threshold required for entry into force. Entry into force will trigger the establishment of a Conference of the Parties empowered to adopt area-based management tools - potentially including high-seas marine protected areas that intersect with major shipping lanes. The ShipCalculators.com calculator catalogue will be updated as BBNJ obligations become operational for commercial shipping.

See also

References

  1. United Nations Convention on the Law of the Sea, 10 December 1982, 1833 UNTS 397, entered into force 16 November 1994.
  2. Agreement relating to the Implementation of Part XI of UNCLOS, 28 July 1994, 1836 UNTS 42.
  3. ITLOS, M/V Saiga (Saint Vincent and the Grenadines v Guinea) (Prompt Release), Case No. 1, Judgment of 4 December 1997.
  4. ITLOS, M/V Saiga (No. 2) (Saint Vincent and the Grenadines v Guinea), Case No. 2, Judgment of 1 July 1999.
  5. Permanent Court of Arbitration, The South China Sea Arbitration (Philippines v China), Case No. 2013-19, Award of 12 July 2016.
  6. ITLOS, Enrica Lexie Incident (Italy v India), Provisional Measures Order, Case No. 24, 24 August 2015; Annex VII Arbitral Tribunal Award, 21 May 2020.
  7. ITLOS, Request for an Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law (COSIS), Advisory Opinion of 21 May 2024.
  8. Agreement under UNCLOS on Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction, adopted 19 June 2023, opened for signature 20 September 2023, UN Doc A/CONF.232/2023/4.
  9. Presidential Proclamation 2667, 28 September 1945, 10 Fed. Reg. 12303 (US Continental Shelf).
  10. IMO Assembly Resolution A.1070(28), IMO Instruments Implementation Code (III Code), adopted 4 December 2013.
  11. D.R. Rothwell and T. Stephens, The International Law of the Sea, 3rd edn (Hart Publishing, 2022).
  12. R.R. Churchill and A.V. Lowe, The Law of the Sea, 3rd edn (Manchester University Press, 1999).
  13. Y. Tanaka, The International Law of the Sea, 3rd edn (Cambridge University Press, 2019).

Further reading

  • Oxman, B.H., “The Territorial Temptation: A Siren Song at Sea” (2006) 100 American Journal of International Law 830.
  • Guilfoyle, D., Shipping Interdiction and the Law of the Sea (Cambridge University Press, 2009).
  • Harrison, J., Saving the Oceans through Law: The International Legal Framework for the Protection of the Marine Environment (Oxford University Press, 2017).
  • Klein, N., Maritime Security and the Law of the Sea (Oxford University Press, 2011).