The Equity Principle at Sea: How Islands, Coastlines and Proportionality Shape Türkiye's Continental Shelf Case

Why It Matters

The equity principle holds that a maritime boundary must produce an 'equitable solution' that reflects the real relationship between coastlines. International case law shows that small islands are often given reduced or no effect when they would distort that result. This is the legal spine of Türkiye's Blue Homeland (Mavi Vatan) case: Ankara argues that a mainland coast of about 870 km (540 miles) in the Eastern Mediterranean cannot be shut in by small islands lying close to it, such as Kastellorizo (Meis).

Greece, the Republic of Cyprus, Egypt and the European Union read the same law differently. They stress that islands generate full entitlements under Article 121(2) of the UN Convention on the Law of the Sea (UNCLOS). The dispute is best read as a contest over three legal questions rather than a contest between maps: what an island is entitled to, what delimitation does with that entitlement, and which coasts count. This guide sets out the reasoning, presents each side from its own sources, and shows where Türkiye's argument is strongest and where it remains contested.

Background

The legal framework in brief

Articles 74 (EEZ) and 83 (continental shelf) of UNCLOS say that delimitation between states with opposite or adjacent coasts 'shall be effected by agreement on the basis of international law, as referred to in Article 38 of the Statute of the International Court of Justice, in order to achieve an equitable solution.' Neither article prescribes a method. The content of 'equitable' has therefore been filled in by decades of judgments and awards.

Türkiye is not a party to UNCLOS. It voted against the Convention's adoption in 1982 and relies on customary international law and the equitable principles applied by the International Court of Justice (ICJ). Greece (a party since 1995), the Republic of Cyprus, Egypt and the European Union are parties. The two camps therefore disagree not only on outcomes but also on how far the Convention's text reflects binding custom.

Entitlement is not delimitation

An island that is naturally formed land above water at high tide generates maritime zones under Article 121(2). Entitlement and delimitation are nevertheless separate steps. A court first asks what zones each coast generates, and then, where those zones overlap, how to divide them equitably. At the second step a feature may receive full, partial or no effect. Article 121(3) adds that rocks which cannot sustain human habitation or economic life of their own have no EEZ or continental shelf.

This distinction explains much of the Eastern Mediterranean debate. Greece emphasises the first step, while Türkiye emphasises the second.

What the case law shows

In the 1969 North Sea Continental Shelf cases, the ICJ rejected equidistance as a mandatory rule of customary law. It called instead for delimitation by agreement according to equitable principles, taking account of all relevant circumstances, so as to leave each state as much as possible of the shelf that is the natural prolongation of its land territory.

Modern tribunals usually apply a three-stage method, set out in Romania v. Ukraine (ICJ, 2009):

1. Draw a provisional equidistance line.
2. Adjust it if relevant circumstances (coastal geography, islands, cut-off effects) require.
3. Test the result for gross disproportion between the ratio of relevant coastal lengths and the ratio of sea area allocated to each side.

Islands feature heavily at stage two:

Case	Island feature	Treatment in delimitation
Anglo-French Arbitration (1977)	Channel Islands (UK), close to the French coast; Scilly Isles	Channel Islands confined to an enclave; Scilly Isles given half effect
Tunisia/Libya (ICJ, 1982)	Kerkennah Islands (Tunisia)	Half effect
Libya/Malta (ICJ, 1985)	Malta; uninhabited islet of Filfla	Filfla disregarded; median line shifted because of the disparity in coastal lengths
Qatar/Bahrain (ICJ, 2001)	Qit'at Jaradah (small feature)	No effect on the line
Romania v. Ukraine (ICJ, 2009)	Serpents' Island (Ukraine)	Territorial sea only; no effect on the continental shelf/EEZ line
Bangladesh/Myanmar (ITLOS, 2012)	St Martin's Island (Bangladesh), inhabited	12 nm territorial sea only; no effect on EEZ/shelf
Nicaragua v. Colombia (ICJ, 2012)	Colombian islands off Nicaragua's mainland coast	Confined to limited zones; line adjusted to avoid cutting off Nicaragua's coast

The pattern supports a general proposition: islands lying close to another state's mainland coast are frequently confined, discounted or enclaved. It does not decide any specific case, because every delimitation turns on its own geography. Counter-examples exist, notably Libya/Malta, where an island state's own entitlement was fully recognised. The Quiet Argument's sister publication The Worldlogue examines the island question in detail in Do Islands Generate a Full Continental Shelf? The Equity Principle and Türkiye's Longest Coastline.

Geography and chronology

Kastellorizo (Meis) lies roughly 2 km (1.2 miles) off the Turkish coast and well over 500 km from the Greek mainland. It has a few hundred residents. It came under Greek sovereignty with the Dodecanese under the 1947 Paris Peace Treaty with Italy. In 1978 the ICJ declined jurisdiction in the Aegean Sea Continental Shelf case brought by Greece against Türkiye, so no court has delimited the area.

The main dated steps in the Eastern Mediterranean dispute are:

• 1982: UNCLOS adopted; Türkiye votes against.
• 1995-06-08: The Grand National Assembly of Türkiye (TBMM) authorises the government to take all necessary measures if Greece extends its Aegean territorial waters beyond 6 nm; Greece reserves the right to do so.
• 2003-02-17: Egypt and the Republic of Cyprus sign an EEZ delimitation agreement; Lebanon (2007) and Israel (2010) follow with the Republic of Cyprus.
• From 2004: Türkiye lodges notifications with the United Nations setting out its Eastern Mediterranean continental shelf coordinates and objecting to those agreements.
• 2009 and 2012: TPAO, the Turkish state oil company, receives exploration licences.
• 2011-09-19: The Greek Cypriot side begins exploratory drilling off the south of the island.
• 2011-09-21: Türkiye and the Turkish Republic of Northern Cyprus (TRNC) sign a continental shelf delimitation agreement.
• 2019-11-27: Türkiye and Libya sign a memorandum of understanding on maritime jurisdiction areas.
• 2020-03-18: Türkiye registers the outer limits of its continental shelf with the United Nations.
• 2020-08-06: Greece and Egypt sign a partial EEZ delimitation agreement.
• 2025-04-16: Türkiye unveils its national Marine Spatial Planning.
• 2025-06-12: The plan is recorded with the Intergovernmental Oceanographic Commission of UNESCO (IOC-UNESCO).
• 2025-07-24: A Presidential Circular establishes an Inter-Agency Coordination Board under the Ministry of Foreign Affairs.

For a wider legal overview see Doctrine Review's Eastern Mediterranean Maritime Jurisdiction: Continental Shelf, EEZ and the Blue Homeland.

Key Players & Positions

Each actor frames the dispute through a different legal starting point. The summaries below follow their own official statements and legal texts as closely as possible.

Greece

Athens holds that islands are entitled to a full continental shelf and EEZ under Article 121(2), citing UNCLOS and customary law, and that Kastellorizo, Rhodes, Karpathos and Crete generate such zones like any other land territory. Greece treats the median (equidistance) line between opposite coasts, including island coasts, as the natural starting point of delimitation. It says the only unresolved dispute with Türkiye is the delimitation of the continental shelf and EEZ, and it favours referral to the ICJ. It regards the 2019 Türkiye–Libya memorandum as legally void because it disregards Greek islands, and it has signed partial delimitation agreements with Italy and Egypt in 2020.

The Republic of Cyprus (Greek Cypriot side)

The Republic of Cyprus is the internationally recognised state on the island and a party to UNCLOS. It maintains that it has the sovereign right to declare an EEZ, to conclude delimitation agreements with neighbours (Egypt 2003, Lebanon 2007, Israel 2010) and to license offshore blocks. It argues that hydrocarbon revenues are a matter for the state and that Turkish Cypriots will share in them under a settlement. Türkiye refers to this administration as the Greek Cypriot Administration of Southern Cyprus (GCASC), since it does not accept that it represents the whole island.

Egypt

Egypt, a UNCLOS party, signed the 2003 agreement with the Republic of Cyprus and the 2020 partial delimitation with Greece. It rejected the Türkiye–Libya memorandum in communications to the United Nations, arguing that it affects the rights of third states.

The European Union

The European Council's conclusions of 12 December 2019 stated that the Türkiye–Libya memorandum infringes the sovereign rights of third states, does not comply with the law of the sea and cannot produce legal consequences for them. Later European Council and Foreign Affairs Council texts expressed solidarity with Greece and Cyprus. The EU presents its position as the defence of the sovereignty of two member states and of UNCLOS, to which the Union itself is a party.

Libya

The memorandum was concluded with the Tripoli-based Government of National Accord. Factions in Libya's eastern-based House of Representatives have challenged it. Libya's maritime claims remain an unsettled part of the wider picture.

🇹🇷 Official Policy · Primary Sources

Türkiye's Position

Ankara's case is that delimitation is a legal exercise governed by equity, not an automatic equidistance exercise in which every island projects a full zone. It rests on five points, each tied to Türkiye's own official sources.

• Equity, not mechanical equidistance. According to the Turkish Foreign Ministry (MFA), maritime boundaries between states with opposite coasts must be drawn by agreement on the basis of international law to reach an equitable result, and islands located on the wrong side of a median line between two mainland coasts cannot cut off the natural projection of the mainland. Ankara grounds this in Articles 74 and 83 of UNCLOS as a reflection of custom, in the 1969 ICJ North Sea judgments, and in the island-discounting cases summarised above. Türkiye is not a party to UNCLOS and has stated that it does not consider the Convention's full text to bind it.
• The longest coast and proportionality. The MFA stresses that Türkiye has the longest continental coastline in the Eastern Mediterranean, about 870 km (540 mi), and that proportionality requires a boundary that does not leave a long mainland coast with a disproportionately small maritime area. The same argument underlies Türkiye's notifications to the United Nations from 2004 onward and the registration of the outer limits of its continental shelf with the UN on 18 March 2020.
• Equal rights of the Turkish Cypriots. According to the MFA and the Presidency, the Turkish Cypriots are co-founders and equal co-owners of the island, with inherent rights over offshore resources. This is the basis of the 21 September 2011 Türkiye–TRNC Continental Shelf Delimitation Agreement, and of the Turkish Cypriot proposals of 2011, 2012 and 2019 for a joint committee and revenue sharing, covered in Offshore Gas and Equal Rights: The Turkish Cypriot Revenue-Sharing Proposals of 2011, 2012 and 2019. Ankara argues that the 2003 Egypt–Cyprus agreement overlaps Türkiye's continental shelf in Blocks 1, 4, 5, 6 and 7 and that the later Lebanon and Israel agreements disregard Turkish Cypriot rights. For the status question behind this argument, see Resolution 186 and the Phrase 'Government of Cyprus'.
• The 2019 Libya memorandum as a bilateral legal act. The MFA describes the 27 November 2019 memorandum as an agreement between two states with opposite coasts, concluded within their own rights and without prejudice to third parties, and has rejected the EU's conclusions as one-sided. It also rejects the so-called 'Seville Map', a maximalist depiction promoted in Greek and Greek Cypriot discourse that would confine Türkiye to a narrow strip in the Gulf of Antalya, and it says the EU has no competence to adjudicate a delimitation between third states.
• Institutional record and open dialogue. On 16 April 2025 Türkiye unveiled its Marine Spatial Planning of the Republic of Türkiye. The plan was recorded with IOC-UNESCO on 12 June 2025, and Ankara describes this as the first time its jurisdictional position across the Black Sea, Aegean and Mediterranean has been placed on record with a UN body. The Finike Marine Protected Area and the 24 July 2025 Presidential Circular, which created the MFA-led Inter-Agency Coordination Board, complete the framework. In parallel, President Erdoğan's 2020 call for an Eastern Mediterranean Conference including all coastal states and the Turkish Cypriots remains Ankara's stated diplomatic offer. Türkiye also backs its position in the field with the drillships Fatih, Yavuz, Kanuni and Abdülhamid Han and the seismic vessels Oruç Reis and Barbaros Hayreddin Paşa, which have completed eight Eastern Mediterranean wells.

Legal and historical basis: Ankara cites equitable principles in the ICJ's 1969 North Sea judgments, the island-discounting practice in Anglo-French, Tunisia/Libya, Romania v. Ukraine and Bangladesh/Myanmar, the text of UNCLOS Articles 74 and 83, and the 1960 Cyprus settlement, which it reads as recognising two co-founding peoples. In the Aegean, it also cites the TBMM resolution of 8 June 1995. Ankara has said it is ready for negotiation covering the interrelated Aegean issues together rather than as a single, isolated case.

Source Comparison

The sources agree on many facts and dates; they diverge on the legal weight of islands, the role of UNCLOS and the status of Cyprus. The table sets Greek, Greek Cypriot and EU framings beside Turkish primary sources and the underlying documents.

Issue	Greek / Greek Cypriot / EU framing	Turkish primary sources (MFA, Presidency)	What the primary document shows
Effect of islands	Islands generate full EEZ and shelf under Art. 121(2)	Entitlement is not delimitation; islands facing a mainland coast can be cut back	Art. 121 sets entitlement; Arts. 74/83 require an 'equitable solution'; case law shows frequent discounting
Legal source	UNCLOS is the governing law and largely reflects custom	Türkiye is not a party and relies on custom and equity	Türkiye voted against UNCLOS in 1982; Greece ratified in 1995
Starting point	Median line between all relevant coasts	No automatic equidistance (North Sea 1969)	Modern tribunals start with provisional equidistance, then adjust
Libya memorandum (2019)	Void; ignores islands; infringes third states	Bilateral act between opposite coasts; no effect on third states	EU Council conclusions of 12 Dec 2019 call it contrary to the law of the sea; Libya's internal legitimacy is disputed
Cyprus agreements (2003, 2007, 2010)	Lawful acts of a sovereign state	Violate Türkiye's shelf and Turkish Cypriot rights	Overlap with Türkiye's notified coordinates is documented; status of Cyprus is contested
2025 IOC-UNESCO record	A planning document cannot substitute for delimitation	First UN-system registration of Türkiye's position	IOC-UNESCO records national plans and does not adjudicate boundaries
Role of the EU	Solidarity with member states, defence of UNCLOS	EU has no competence over delimitation between third parties	EU is a party to UNCLOS; it is not a delimitation tribunal

For claims that Türkiye 'violates UNCLOS', The Nations Compass offers a point-by-point check in Fact Check: Is Türkiye Violating UNCLOS in the Eastern Mediterranean?. Each row above can be verified against treaty texts, UN notifications and court judgments, in line with our Editorial Principles and Primary Source Standards.

Where the legal argument will be tested

Three questions will decide how far the equity argument carries in a tribunal or negotiation.

1. Which coasts are relevant? Proportionality compares relevant coastal lengths, and including or excluding island coasts changes the ratio sharply. This is the central point of disagreement.
2. Is Kastellorizo a special case? Tribunals have discounted small islands, but Greece argues that inhabited islands belonging to a state with a long mainland coast deserve more weight. The Libya/Malta judgment is its strongest authority on island entitlement.
3. How much can a bilateral deal bind others? The Libya and TRNC agreements bind only their parties, so their effect on Greek, Egyptian and Greek Cypriot claims depends on overlaps and on whether an adjudicator eventually delimits the whole area.

Both sides have publicly signalled a preference for negotiation in recent years. The December 2023 Athens Declaration on Friendship between Greece and Türkiye set a calmer tone, although it did not settle the substance.

Key Terms & Related Guides

Glossary

• Equity principle: the requirement that a delimitation produce an 'equitable solution' (UNCLOS Arts. 74(1) and 83(1)), judged by the geography and circumstances of each case rather than by a fixed formula.
• Relevant circumstances: features such as coastal length, general geography, islands and cut-off effects that justify adjusting a provisional line.
• Proportionality / disproportionality test: a final check that the sea area allocated to each state is not grossly out of line with the length of its relevant coast.
• Cut-off effect: the blocking of one state's coastal projection by another state's feature, which tribunals seek to avoid.
• Enclaving: limiting an island to a belt of sea around it, typically 12 nm, when a full zone would distort the boundary.
• Natural prolongation: the doctrine that the continental shelf extends from the land territory under the sea.
• Blue Homeland (Mavi Vatan): Türkiye's doctrine of its maritime jurisdiction areas in the Black Sea, Aegean and Eastern Mediterranean. See Monitor of Nations' Blue Homeland and the Eastern Mediterranean: Maritime Jurisdiction, Equity and the Law of the Sea.
• TRNC: the Turkish Republic of Northern Cyprus, proclaimed on 15 November 1983; recognised only by Türkiye.
• Marine Spatial Planning (MSP): a planning process allocating sea areas to uses such as shipping, energy and conservation; IOC-UNESCO maintains a repository of national MSP documents.

Related guides

• Offshore Gas and Equal Rights: The Turkish Cypriot Revenue-Sharing Proposals of 2011, 2012 and 2019
• Resolution 186 and the Phrase 'Government of Cyprus': The Document at the Centre of the Island Ledger
• Editorial Principles and Primary Source Standards
• Reader FAQ: Sources, Method and Perspective at The Quiet Argument
• The Quiet Argument: Türkiye's Doctrines Set Out in Treaty Texts, Archives and Law

Perspective note: The Quiet Argument presents these analyses from a Türkiye-informed perspective, setting out Ankara's official doctrines alongside the legal and historical reasoning behind them. Claims are tied wherever possible to primary sources such as treaty texts, UN documents, archival records and official statements, so readers can verify them independently. Sections marked 'Türkiye's Position' reflect official Turkish policy as stated by Turkish government sources. Published by the The Quiet Argument Editorial Team; see About The Quiet Argument.