Maritime Delimitation

Introduction

Maritime delimitation is the process of determining the boundary between the maritime zones or maritime entitlements of States with opposite or adjacent coasts.

It becomes necessary when the maritime entitlements of two or more States overlap.

The principal framework is found in UNCLOS, particularly:

• Article 15 → Territorial sea delimitation
• Article 74 → EEZ delimitation
• Article 83 → Continental shelf delimitation

The central objective is to achieve an equitable solution while respecting the relevant maritime entitlements and geographical circumstances.

Core Formula

Overlapping Maritime Entitlements

↓

Identify the Applicable Zone

↓

Construct Provisional Equidistance Line

↓

Consider Relevant Circumstances

↓

Adjust if Necessary

↓

Check for Disproportionality

↓

Equitable Result

Meaning of Maritime Delimitation

Maritime delimitation is different from simply measuring a maritime zone.

Maritime Entitlement

Determines how far a State may claim a maritime zone under international law.

Maritime Delimitation

Determines where the boundary lies between overlapping entitlements of two or more States.

For example:

If State A and State B are close enough that their 200-nautical-mile EEZs overlap, both cannot exercise exclusive rights over the same area.

A boundary must therefore be established.

Why Maritime Delimitation Is Necessary

Delimitation is required because States may have overlapping claims concerning:

• territorial seas;
• EEZs;
• continental shelves.

It is particularly important where States have:

• opposite coasts;
• adjacent coasts;
• islands;
• irregular coastlines;
• narrow seas;
• competing continental-shelf claims.

Maritime Delimitation vs Maritime Boundary

These terms are closely related but can be distinguished.

Delimitation

The legal process of determining the boundary.

Maritime Boundary

The resulting line separating the maritime areas of the States concerned.

Main UNCLOS Provisions

Article 15

Concerns delimitation of the territorial sea between States with opposite or adjacent coasts.

Article 74

Concerns delimitation of the EEZ.

Article 83

Concerns delimitation of the continental shelf.

The rules are not identical.

Territorial Sea Delimitation

Article 15 UNCLOS

Where the coasts of two States are opposite or adjacent, neither State is entitled, in the absence of agreement, to extend its territorial sea beyond the median line whose points are equidistant from the nearest points on the baselines.

However, an exception exists where:

• historic title exists; or
• special circumstances justify a different boundary.

Basic Rule

Median Line

↓

unless

Historic Title / Special Circumstances

↓

Different boundary may be appropriate.

Median Line

A median line is generally constructed so that each point on the line is equidistant from the nearest points on the baselines of the two States.

It is often called the:

Equidistance Line

For territorial-sea delimitation, Article 15 gives equidistance a particularly direct role.

Special Circumstances

The median line is not necessarily absolute.

Special circumstances may justify a different boundary.

Examples may include:

• unusual coastal geography;
• certain islands;
• unstable or highly irregular coastlines;
• other circumstances recognised by applicable international law.

EEZ Delimitation

Article 74 UNCLOS

The delimitation of the EEZ between States with opposite or adjacent coasts must be effected by:

Agreement

on the basis of international law referred to in Article 38 of the ICJ Statute, in order to achieve an:

Equitable Solution

This is different from the wording of Article 15.

Article 74 does not simply prescribe a median line.

Continental Shelf Delimitation

Article 83 UNCLOS

The continental shelf between States with opposite or adjacent coasts must likewise be delimited by:

Agreement

on the basis of international law referred to in Article 38 of the ICJ Statute, in order to achieve an:

Equitable Solution

Therefore:

Article 74 → EEZ → Equitable Solution

Article 83 → Continental Shelf → Equitable Solution

Equitable Solution

The expression “equitable solution” is central to modern maritime delimitation.

It does not mean:

Every State must receive exactly the same area.

Nor does it mean:

The boundary must automatically follow the coastline.

Instead, the boundary should produce a result that is equitable in light of the relevant geographical and legal circumstances.

Modern Three-Stage Method

Modern international courts and tribunals have developed a structured methodology, particularly for EEZ and continental shelf delimitation.

Stage One: Provisional Equidistance Line

The tribunal normally constructs a:

Provisional equidistance line

using appropriate base points.

Stage Two: Relevant Circumstances

The tribunal considers whether there are circumstances requiring adjustment of the provisional line.

These may include:

• significant coastal-length differences;
• concavity;
• coastal configurations;
• islands;
• cut-off effects;
• geographic circumstances;
• other legally relevant factors.

Stage Three: Disproportionality Test

The resulting boundary is checked against the relevant coastal lengths and maritime areas.

The purpose is to determine whether the result produces a marked or gross disproportionality.

Complete Formula

Equidistance

↓

Relevant Circumstances

↓

Adjustment

↓

Disproportionality Check

↓

Equitable Solution

Important Point

This three-stage methodology is not written word-for-word in Articles 74 and 83.

It has been developed through the jurisprudence of international courts and tribunals interpreting and applying the broader requirement of an equitable solution.

Equidistance vs Equity

Modern delimitation law does not treat:

Equidistance

and

Equity

as completely opposing concepts.

Equidistance is often the starting point.

Equity operates through consideration of relevant circumstances and the assessment of the final result.

Therefore:

Equidistance is a Method; Equity Is the Objective.

Relevant Circumstances

Relevant circumstances depend on the particular geography and facts of the case.

Commonly considered circumstances include:

Coastal Configuration

A highly irregular or concave coastline may distort an equidistance line.

Disproportionate Coastal Length

A significant difference in relevant coastal lengths may be relevant to assessing the result.

Islands

An island may receive:

• full effect;
• partial effect;
• reduced effect;
• no effect

depending on the circumstances.

There is no universal rule that every island must receive identical treatment.

Cut-Off Effect

A boundary may be adjusted where an equidistance line effectively cuts off one State’s access to its maritime projection.

Geography

The tribunal primarily focuses on geographical factors directly connected with delimitation.

Islands in Maritime Delimitation

Islands can significantly affect maritime boundaries.

An island may generate:

• territorial sea;
• EEZ;
• continental shelf,

depending on Article 121 and other applicable rules.

But the existence of an entitlement does not necessarily mean that the island must receive full effect in delimitation.

Rocks under Article 121(3)

Rocks that cannot sustain human habitation or economic life of their own do not generate:

• EEZ;
• continental shelf.

This may substantially affect delimitation.

Islands and Delimitation

The tribunal may consider whether giving an island full effect would create:

• an inequitable result;
• disproportionate maritime projection;
• cut-off of another State’s coast.

Therefore:

Entitlement ≠ Automatic Full Effect

Concave Coasts

Concavity can be particularly important.

Where an equidistance line generated by a concave coastline causes the maritime projection of a State to be significantly cut off, adjustment may be considered.

Coastal Length

Coastal length can be relevant to the proportionality assessment.

However, it is not a mathematical rule that:

Longer coastline = proportionally larger maritime area.

The overall geographical circumstances remain decisive.

Relevant Coast

Courts distinguish between the:

• entire geographical coastline;
• relevant coast for the particular delimitation.

Only the coast relevant to generating or assessing the maritime entitlements in dispute is normally considered.

Provisional Equidistance Line

The first-stage line must be constructed using appropriate base points.

The selection of base points can significantly affect the line.

Therefore, tribunals carefully assess:

• which coastal points are appropriate;
• whether particular islands should be used;
• whether unstable or exceptional geographical features should influence the line.

Adjustment of the Line

If relevant circumstances exist, the provisional line may be adjusted.

The adjustment must remain connected to the objective of achieving an equitable solution.

It cannot simply be based on political preference.

Disproportionality Test

The final stage does not seek perfect mathematical equality.

Instead, the tribunal asks whether there is a significant disproportionality between:

• relevant coastal lengths;
• maritime areas allocated.

The test is primarily a safeguard against an obviously inequitable outcome.

Delimitation by Agreement

Articles 74 and 83 emphasise:

Agreement between States

States are encouraged to negotiate and conclude maritime boundaries by agreement.

Where they cannot agree, they may use:

• negotiation;
• mediation;
• conciliation;
• arbitration;
• ITLOS;
• ICJ;
• other agreed procedures.

Provisional Arrangements

Articles 74(3) and 83(3)

Pending final agreement, States should:

• make every effort to enter into provisional arrangements of a practical nature;
• make every effort not to jeopardise or hamper the reaching of a final agreement.

These provisions are important where delimitation remains unresolved.

Unresolved Boundary Does Not Mean No Rights

The absence of a final boundary does not necessarily mean that neither State has maritime rights.

The problem is that overlapping claims must be managed without prejudicing the eventual delimitation.

Obligation Not to Jeopardise or Hamper

States involved in an unresolved delimitation must avoid conduct that:

• prejudices the final boundary;
• makes agreement more difficult;
• irreversibly changes the disputed area.

This is particularly relevant to:

• resource exploitation;
• drilling;
• construction;
• permanent installations.

Provisional Arrangements vs Final Delimitation

These should not be confused.

Provisional Arrangement

Temporary/practical cooperation pending final boundary.

Final Delimitation

Legally establishes the maritime boundary.

Joint Development

States may agree to jointly exploit resources in a disputed maritime area.

This can be useful where:

• delimitation is politically difficult;
• hydrocarbons or fisheries are important;
• both States want to avoid conflict.

Joint development does not necessarily determine the final boundary.

Maritime Delimitation and Natural Resources

Delimitation can determine control over:

• oil;
• natural gas;
• fisheries;
• minerals;
• seabed resources.

Therefore, maritime boundary disputes can have major economic consequences.

Territorial Sea vs EEZ/Continental Shelf Delimitation

The rules should not be treated as identical.

Territorial Sea

Article 15:

Median/equidistance line

subject to:

• historic title;
• special circumstances.

EEZ

Article 74:

Agreement + international law → equitable solution

Continental Shelf

Article 83:

Agreement + international law → equitable solution

Maritime Delimitation vs Delineation

These terms are sometimes confused.

Delimitation

Determining the boundary between States.

Delineation

Determining the outer limits of a maritime zone, particularly the outer continental shelf.

For example:

CLCS

The Commission on the Limits of the Continental Shelf deals with scientific and technical recommendations concerning the outer limits of the continental shelf beyond 200 nautical miles.

It does not decide maritime boundaries between States.

Delimitation vs CLCS

Maritime Delimitation	CLCS Outer-Limit Process
Boundary between States	Outer limit of continental shelf
Bilateral/multilateral	Scientific/technical
Courts/tribunals/States	CLCS
Resolves overlapping claims	Does not delimit boundaries
Articles 15, 74, 83	Article 76 + Annex II

Maritime Delimitation and the Continental Margin

A State may have an entitlement to a continental shelf beyond 200 nautical miles under Article 76.

But that entitlement does not automatically determine the boundary with another State.

Where claims overlap:

Entitlement First → Delimitation Second

Delimitation of the Extended Continental Shelf

Where States have overlapping claims to an extended continental shelf, delimitation between them remains a matter for the States or the competent court/tribunal.

CLCS recommendations concerning outer limits do not themselves settle the boundary between neighbouring States.

Important Case: North Sea Continental Shelf

North Sea Continental Shelf (Germany v Denmark; Germany v Netherlands)

The ICJ’s 1969 judgment is one of the foundational decisions on continental-shelf delimitation.

The Court rejected the argument that the equidistance principle in Article 6 of the 1958 Continental Shelf Convention automatically bound Germany in the circumstances.

It emphasised:

• equitable principles;
• relevant circumstances;
• the need to take account of the geographical situation;
• proportionality as an important consideration.

Examination Point

North Sea Continental Shelf → Equitable principles + relevant circumstances + continental shelf delimitation

Important Case: Tunisia/Libya

Continental Shelf (Tunisia/Libyan Arab Jamahiriya)

The ICJ emphasised that delimitation must be achieved through:

Equitable principles + relevant circumstances

The case contributed significantly to the development of modern equitable delimitation.

Important Case: Libya/Malta

Continental Shelf (Libyan Arab Jamahiriya/Malta)

The Court considered:

• equidistance;
• relevant circumstances;
• proportionality;
• geographical considerations.

It further developed the modern approach to maritime delimitation.

Important Case: Maritime Delimitation in the Black Sea

Romania v Ukraine

This is one of the clearest modern authorities on the three-stage methodology.

The ICJ:

1. constructed a provisional equidistance line;
2. examined relevant circumstances;
3. checked the result for significant disproportionality.

Examination Point

Black Sea → Three-stage delimitation method

Important Case: Bangladesh/Myanmar

Bangladesh/Myanmar before ITLOS

The Tribunal addressed maritime delimitation involving:

• territorial sea;
• EEZ;
• continental shelf.

It applied equitable principles and developed the modern methodology for delimitation.

Important Case: Bangladesh/India

Bay of Bengal Maritime Boundary Arbitration

The arbitral tribunal addressed the maritime boundary between Bangladesh and India.

The case is important for:

• equidistance;
• relevant circumstances;
• equitable solution;
• maritime boundary adjustment.

Important Case: Qatar v Bahrain

Maritime Delimitation and Territorial Questions between Qatar and Bahrain

The ICJ dealt with:

• territorial sovereignty;
• islands;
• maritime delimitation.

It is particularly useful for understanding the relationship between territorial questions and maritime boundaries.

Important Case: Ghana/Côte d’Ivoire

Ghana/Côte d’Ivoire

The Special Chamber of ITLOS addressed the delimitation of the maritime boundary between the two States.

The decision is useful for:

• equidistance;
• relevant circumstances;
• equitable solution;
• maritime boundary methodology.

Important Case: Guyana v Venezuela

The ICJ has also considered issues relating to the maritime boundary dispute between Guyana and Venezuela.

The case illustrates the importance of:

• jurisdiction;
• territorial questions;
• maritime delimitation.

Important Case: Nicaragua v Colombia

The ICJ’s maritime delimitation jurisprudence involving Nicaragua and Colombia is highly relevant to:

• maritime entitlements;
• islands;
• territorial sea;
• EEZ;
• continental shelf;
• boundary construction.

Three-Stage Method — Exam Format

Stage One

Construct Provisional Equidistance Line

Determine appropriate base points and construct the provisional line.

↓

Stage Two

Identify Relevant Circumstances

Consider whether geographical circumstances require adjustment.

Examples:

• islands;
• concavity;
• coastal configuration;
• cut-off effects;
• significant geographical differences.

↓

Stage Three

Disproportionality Check

Compare relevant coastal lengths and resulting maritime areas.

↓

Final Boundary

Equitable Solution

Equity Does Not Mean Ex Aequo et Bono

This is an important distinction.

Equitable Principles

Apply international law to achieve an equitable result.

Ex Aequo et Bono

A court may decide according to considerations of fairness rather than strictly according to law only where the parties agree, under Article 38(2) of the ICJ Statute.

Therefore:

Equitable Solution ≠ Ex Aequo et Bono

Geography Is the Central Factor

Maritime delimitation primarily concerns:

Geography

rather than broader political or economic considerations.

Courts generally avoid treating unrelated factors as decisive.

Security Considerations

Security concerns may be relevant in particular cases, but they do not automatically determine a maritime boundary.

The delimitation exercise remains governed primarily by the applicable legal rules and geographical circumstances.

Economic Factors

Economic factors generally do not determine the boundary by themselves.

A State cannot ordinarily claim:

“We need more maritime territory because the area contains valuable resources.”

Resource value is not normally a free-standing basis for shifting a boundary.

Fisheries

Fisheries may be important in the broader dispute, but fish stocks do not automatically determine the maritime boundary.

Special fisheries agreements may be used to manage resources.

Islands and Half-Effect

Courts sometimes give an island:

• full effect;
• half effect;
• reduced effect;
• no effect

in constructing a maritime boundary.

But “half-effect” is not a universal rule.

It is a case-specific technique used where appropriate.

Maritime Boundary and Baselines

Baselines are fundamental because they determine the starting point for measuring maritime zones.

Therefore:

Baseline → Entitlement → Delimitation

An improper baseline can produce an improper maritime claim.

Opposite Coasts

Two States have opposite coasts where their coasts face each other across a maritime area.

Examples may involve:

State A → Sea → State B

Their maritime zones may overlap.

Adjacent Coasts

Two States have adjacent coasts where their coastlines meet or lie alongside each other.

Delimitation can be more complicated because of:

• coastal configuration;
• concavity;
• islands;
• coastal projections.

Multiple-State Delimitation

A maritime area can involve more than two States.

In such circumstances, the tribunal must consider:

• the claims of all relevant States;
• existing boundaries;
• applicable agreements;
• the rights of third States.

A court generally cannot determine the rights of a third State without the necessary jurisdictional basis.

Maritime Delimitation and Third States

A bilateral delimitation cannot lawfully prejudice the established rights of a third State.

This is particularly important where:

• three States share a sea;
• maritime claims overlap;
• a boundary could affect another State’s entitlement.

Maritime Delimitation and Unilateral Claims

A State cannot establish a maritime boundary merely by issuing domestic legislation or a unilateral proclamation.

A boundary between States generally requires:

• agreement;
• accepted international legal process;
• or adjudication/arbitration based on jurisdictional consent.

Role of International Courts and Tribunals

Maritime delimitation may be determined by:

• ICJ;
• ITLOS;
• Annex VII arbitral tribunals;
• other agreed arbitral tribunals.

The relevant jurisdictional basis must exist.

UNCLOS Dispute Settlement

Part XV UNCLOS provides mechanisms for resolving disputes.

Important provisions include:

• Article 279 → peaceful settlement
• Article 286 → compulsory procedures
• Article 287 → choice of procedure
• Article 288 → jurisdiction
• Article 298 → optional exceptions/declarations

Maritime delimitation disputes may be subject to limitations and exceptions under the particular circumstances and declarations of the States concerned.

Maritime Delimitation and Article 298

States may make optional declarations excluding certain categories of disputes from compulsory procedures under Article 298.

One important category concerns:

maritime boundary disputes

subject to the conditions of the provision.

Therefore, UNCLOS does not mean that every maritime boundary dispute automatically goes to a court or tribunal.

Important Distinctions

Delimitation vs Entitlement

Entitlement → How far a State may claim

Delimitation → Where overlapping claims are divided

Delimitation vs Demarcation

Delimitation → Legal boundary

Demarcation → Physical marking of the boundary

Delimitation vs Delineation

Delimitation → Boundary between States

Delineation → Outer limit of a maritime zone

Common Examination Mistakes

Mistake 1: Every Maritime Boundary Uses the Median Line

Incorrect.

Article 15 specifically provides the median-line rule for territorial-sea delimitation, subject to exceptions.

EEZ and continental-shelf delimitation under Articles 74 and 83 is directed toward an equitable solution.

Mistake 2: Equidistance Is the Final Rule in Every Case

Incorrect.

For EEZ and continental shelf, it is generally a starting methodology rather than an automatic final boundary.

Mistake 3: Equity Means Equal Areas

Incorrect.

An equitable solution does not require equal areas.

Mistake 4: Every Island Gets Full Effect

Incorrect.

Islands may receive reduced or no effect depending on the circumstances.

Mistake 5: Half-Effect Is Mandatory for Islands

Incorrect.

It is a case-specific technique, not a universal rule.

Mistake 6: CLCS Delimits Maritime Boundaries

Incorrect.

CLCS deals with outer continental-shelf limits and does not delimit boundaries between States.

Mistake 7: Unresolved Delimitation Means No Rights Exist

Incorrect.

States may have overlapping entitlements, but they must manage them consistently with international law pending final delimitation.

Mistake 8: Resource Wealth Automatically Changes the Boundary

Incorrect.

Economic considerations are not normally a decisive independent basis for maritime delimitation.

Mistake 9: Delimitation and Demarcation Are the Same

Incorrect.

Delimitation establishes the legal boundary; demarcation physically marks it.

Mistake 10: Articles 74 and 83 Give an Exact Formula

Incorrect.

They require agreement and an equitable solution; the detailed methodology has been developed through international jurisprudence.

Quick Revision

• Maritime delimitation → determining maritime boundaries between States.
• Main UNCLOS provisions:
  • Article 15 → territorial sea
  • Article 74 → EEZ
  • Article 83 → continental shelf
• Territorial sea → median/equidistance line, subject to historic title/special circumstances.
• EEZ → agreement + international law → equitable solution.
• Continental shelf → agreement + international law → equitable solution.
• Modern methodology generally has three stages:
  1. provisional equidistance line;
  2. relevant circumstances;
  3. disproportionality check.
• Equidistance is generally a starting point for EEZ/continental shelf delimitation.
• Objective → equitable solution.
• Equity does not mean equal area.
• Geography is central.
• Relevant circumstances may include:
  • islands;
  • concavity;
  • coastal configuration;
  • cut-off effects;
  • significant coastal-length differences.
• Islands do not necessarily receive full effect.
• Half-effect is not automatic.
• Article 74(3) and 83(3) → provisional arrangements and duty not to jeopardise/hamp­er final agreement.
• CLCS → outer limits of extended continental shelf, not maritime boundary delimitation.
• Delimitation ≠ demarcation.
• Delimitation ≠ delineation.
• Entitlement ≠ delimitation.
• Important cases:
  • North Sea Continental Shelf
  • Tunisia/Libya
  • Libya/Malta
  • Romania v Ukraine (Black Sea)
  • Bangladesh/Myanmar
  • Bangladesh/India
  • Qatar v Bahrain
  • Ghana/Côte d’Ivoire
  • Nicaragua v Colombia
• Core formula:

Equidistance → Relevant Circumstances → Disproportionality → Equitable Solution

One-Line Memory Trick

“15 – 74 – 83”

15 → Territorial Sea

74 → EEZ

83 → Continental Shelf

And:

“E-R-D”

E → Equidistance

R → Relevant Circumstances

D → Disproportionality

↓

Equitable Boundary

Final Delimitation Formula

Overlapping Entitlements

↓

Identify Maritime Zone

↓

Territorial Sea

Article 15

→ Median Line

→ Historic Title / Special Circumstances

↓

EEZ

Article 74

→ Agreement

→ International Law

→ Equitable Solution

↓

Continental Shelf

Article 83

→ Agreement

→ International Law

→ Equitable Solution

↓

Modern Methodology

Provisional Equidistance

↓

Relevant Circumstances

↓

Adjustment

↓

Disproportionality Check

↓

Final Equitable Boundary

Conclusion

Maritime delimitation is the legal process through which overlapping maritime entitlements of States are converted into a defined maritime boundary.

The three most important UNCLOS provisions are:

Article 15 → Territorial Sea

Article 74 → EEZ

Article 83 → Continental Shelf

Article 15 gives a more specific median-line/equidistance rule, subject to historic title and special circumstances. Articles 74 and 83, by contrast, require States to reach an agreement based on international law in order to achieve an equitable solution.

International jurisprudence has developed a structured approach for EEZ and continental-shelf delimitation. The modern methodology generally begins with a provisional equidistance line, examines relevant circumstances, makes any necessary adjustment, and finally checks the result for significant disproportionality.

The most important lesson is that:

Equidistance is generally the starting point, not an automatic final answer.

Similarly:

Equity does not mean equal division.

The final boundary must reflect the relevant geographical and legal circumstances.

The leading cases include North Sea Continental Shelf, Tunisia/Libya, Libya/Malta, Romania v Ukraine (Black Sea) and Bangladesh/Myanmar. The Black Sea case is particularly useful for remembering the modern three-stage methodology.

For examination purposes, remember:

15 – 74 – 83

15 → Territorial Sea

74 → EEZ

83 → Continental Shelf

and:

Equidistance → Relevant Circumstances → Disproportionality → Equitable Solution

Ultimately, maritime delimitation seeks to reconcile competing maritime entitlements while ensuring that the resulting boundary is consistent with international law and an equitable solution.