Introduction

International maritime boundary energy disputes arise when two or more States have overlapping claims over maritime areas containing oil, natural gas, offshore wind resources, seabed minerals, or other energy resources. These disputes are particularly significant because maritime boundaries determine which State possesses sovereign rights to explore, exploit, conserve and manage natural resources.

The legal framework is primarily derived from the United Nations Convention on the Law of the Sea (UNCLOS). The most important zones are the territorial sea, exclusive economic zone (EEZ), and continental shelf. Under UNCLOS, coastal States exercise sovereign rights over natural resources in their EEZ and continental shelf, but overlapping claims can make it difficult to determine which State is legally entitled to develop a particular oil or gas field.

International courts and tribunals have therefore developed principles concerning maritime delimitation, provisional arrangements, unilateral resource exploitation, equitable solutions, good-faith negotiations and the duty not to jeopardize or hamper a final agreement.

1. Meaning and Nature of Maritime Boundary Energy Disputes

A maritime boundary energy dispute normally occurs in one of three situations:

Uncertain or disputed maritime boundary
Two States claim the same offshore area.

Energy resources straddling a boundary
A petroleum or gas reservoir extends across an established or proposed maritime boundary.

Energy activities undertaken before delimitation
One State grants an oil concession, conducts seismic surveys, drills wells or authorizes offshore development in an area claimed by another State.

These disputes combine law of the sea, energy law, international environmental law, investment law and sometimes international arbitration.

2. UNCLOS Legal Framework

A. Territorial Sea

Under UNCLOS, the territorial sea can extend up to 12 nautical miles from the baseline. The coastal State exercises sovereignty over this zone, subject to international law.

Where States have opposite or adjacent coasts, the territorial-sea boundary generally involves a median or equidistance line unless another boundary has been agreed or special circumstances justify a different solution.

B. Exclusive Economic Zone

The EEZ may extend up to 200 nautical miles. The coastal State possesses sovereign rights for the exploration and exploitation of natural resources, including:

oil;

natural gas;

offshore renewable energy;

seabed resources; and

other economic resources.

C. Continental Shelf

The continental shelf concerns seabed and subsoil resources. The coastal State has sovereign rights for exploring and exploiting those resources.

This is particularly important for offshore petroleum because hydrocarbons may exist beneath the seabed far beyond the territorial sea.

D. Articles 74 and 83 of UNCLOS

Articles 74 and 83 concern delimitation of the EEZ and continental shelf respectively.

Where States have overlapping claims, they are required to seek an agreement on the basis of international law in order to achieve an equitable solution.

Pending agreement, Article 74(3) and Article 83(3) require States to:

make every effort to enter into provisional arrangements of a practical nature; and

refrain from conduct that would jeopardize or hamper the reaching of a final agreement.

This obligation is particularly important in offshore energy disputes.

3. Importance of Energy Resources in Maritime Delimitation

Oil and gas activities can have two different legal roles.

First: Evidence concerning the boundary

Long-standing oil concessions or exploration activities may sometimes provide evidence concerning how States themselves understood a maritime boundary.

However, the existence of oil concessions does not automatically establish an international boundary.

Second: A source of dispute

A State may argue that another State has unlawfully:

issued petroleum licences;

conducted seismic surveys;

drilled exploratory wells;

constructed offshore platforms; or

exploited hydrocarbons

in an area whose ownership is disputed.

The courts therefore distinguish between evidence relevant to delimitation and unilateral conduct that cannot itself create sovereignty.

4. Ghana/Côte d'Ivoire: A Major Offshore Oil Case

Dispute concerning Delimitation of the Maritime Boundary between Ghana and Côte d'Ivoire, ITLOS Special Chamber, 2017

This is one of the most important modern examples of an energy-related maritime boundary dispute.

The dispute concerned the maritime boundary between Ghana and Côte d'Ivoire in the Atlantic Ocean. Offshore petroleum activities were particularly important because both States had undertaken oil exploration and had granted concessions in the relevant maritime area. The case was submitted to a Special Chamber of ITLOS, which delivered its Judgment on 23 September 2017. (ITLOS)

Oil practice

Ghana argued that decades of oil concessions, seismic surveys and drilling activities demonstrated the existence of a tacitly agreed maritime boundary. The record shows that both States relied heavily on their respective offshore petroleum practices. (ITLOS)

The case therefore raised an important question:

Can long-standing petroleum activity demonstrate the existence of a maritime boundary?

The answer is highly fact-dependent. Oil concessions may constitute relevant evidence, but petroleum practice must be examined alongside the broader conduct of the States and the requirements of international maritime delimitation.

Provisional measures

During the proceedings, Côte d'Ivoire requested provisional measures under UNCLOS Article 290. The Special Chamber prescribed provisional measures on 25 April 2015. (ITLOS)

This demonstrates an important feature of energy disputes: courts may need to protect the disputed area while the final boundary question is being determined.

Legal significance

The Ghana/Côte d'Ivoire dispute demonstrates that:

petroleum concessions cannot automatically create sovereignty;

historical oil practice can nevertheless be relevant evidence;

unilateral offshore activity can create serious legal consequences;

provisional measures can prevent escalation;

States should cooperate while maritime delimitation remains unresolved.

5. Guyana/Suriname Arbitration, 2007

Guyana v. Suriname, PCA Arbitration under UNCLOS

This dispute is particularly important because it involved oil concessions and drilling activities in a disputed maritime area.

Guyana initiated arbitration under Annex VII of UNCLOS in 2004. The dispute concerned the maritime boundary and alleged breaches arising from activities connected with Guyana's oil concessions. In 2000, Suriname's navy ordered an oil rig and drill ship to leave the disputed area. (PCA CPA)

The tribunal ultimately issued its award on 17 September 2007. (PCA CPA)

Legal significance

The case illustrates the danger of treating a disputed offshore area as though sovereignty were already settled.

The dispute involved:

maritime delimitation;

petroleum concessions;

drilling;

use of force or coercive measures;

provisional arrangements; and

Articles 74(3) and 83(3) of UNCLOS.

The tribunal considered the obligation of States to make every effort to reach provisional arrangements and not to jeopardize or hamper the final settlement.

Energy-law lesson

An offshore petroleum licence issued by one State does not eliminate the legal uncertainty created by an overlapping maritime claim. Energy companies operating in disputed areas therefore face significant sovereign-risk and investment-risk exposure.

6. Romania v. Ukraine — Black Sea Maritime Delimitation

Maritime Delimitation in the Black Sea, ICJ, 2009

The ICJ's judgment in Romania v. Ukraine is a leading authority on maritime delimitation.

The Court established a single maritime boundary delimiting the continental shelf and EEZs of the two States. (International Court of Justice)

Importantly, the Court considered the conduct of the parties, including:

oil and gas concessions;

fishing activities; and

naval patrols.

However, the Court did not consider the oil and gas concession practice sufficient to justify changing the provisional equidistance line. (International Court of Justice)

Principle

This case illustrates that energy-related conduct is relevant but not necessarily determinative.

The Court's methodology involved:

identifying the relevant coasts;

constructing a provisional equidistance line;

considering relevant circumstances;

determining whether adjustment was required; and

checking proportionality to ensure that the result was not inequitable.

Importance for energy law

A petroleum company cannot assume that existing concession boundaries will determine the eventual international maritime boundary.

7. Somalia v. Kenya, 2021

Maritime Delimitation in the Indian Ocean

In Somalia v. Kenya, the ICJ determined the maritime boundary between the two States in 2021.

The dispute concerned the territorial sea, EEZ and continental shelf. The Court rejected Kenya's claim that an agreed maritime boundary followed a parallel of latitude and established a maritime boundary using a geodetic line for the EEZ and continental shelf. (International Court of Justice)

The proceedings also involved evidence relating to offshore concessions and maritime resource areas. The ICJ case record includes material concerning Somali and Kenyan concession blocks. (International Court of Justice)

Energy significance

The case demonstrates why petroleum licensing systems must account for unresolved maritime boundaries. A State's domestic licensing decisions cannot necessarily determine the international legal entitlement to offshore resources.

8. Tunisia/Libya Continental Shelf Case

Continental Shelf (Tunisia/Libyan Arab Jamahiriya), ICJ, 1982

The Tunisia/Libya case is a foundational authority concerning the relevance of petroleum activities in maritime delimitation.

The Court considered the existence of a de facto line created partly through the way the parties had initially granted offshore exploration and exploitation concessions. The oil-concession practice was regarded as a relevant circumstance in the delimitation analysis. (ITLOS)

This case is especially important because it demonstrates that petroleum practice can sometimes provide evidence concerning the parties' conduct.

However, the case should not be interpreted as establishing a general rule that oil concessions create maritime boundaries.

The correct principle is narrower:

Consistent and mutually observed petroleum practice may be a relevant circumstance when determining maritime delimitation, depending on the particular facts.

9. Equidistance and Equitable Solution

Modern maritime delimitation generally focuses on achieving an equitable result.

International courts frequently use a methodology involving:

Step 1 — Provisional equidistance line

A provisional line is constructed between the relevant coasts.

Step 2 — Relevant circumstances

The tribunal considers whether circumstances justify adjustment.

Possible circumstances include:

unusual coastal geography;

islands;

coastal configuration;

existing agreements;

relevant State conduct;

the presence of third-State rights;

proportionality; and

other circumstances recognized by international law.

Step 3 — Disproportionality test

The resulting maritime areas and relevant coastal lengths may be compared to ensure that the delimitation does not produce a manifestly disproportionate result.

The Romania/Ukraine judgment provides an important illustration of this methodology. (International Court of Justice)

10. Straddling Petroleum Deposits

A particularly difficult situation occurs where a petroleum reservoir crosses a maritime boundary.

Suppose:

State A | Maritime boundary | State B

and the same geological reservoir extends underneath both sides.

The legal boundary does not automatically move merely because the geological reservoir crosses it.

Possible solutions include:

joint development agreements;

unitization agreements;

joint operating arrangements;

revenue-sharing arrangements;

coordinated licensing;

information-sharing mechanisms; and

provisional arrangements pending final delimitation.

Such arrangements allow States to exploit resources without prejudicing their respective sovereignty claims.

11. Duty Not to Jeopardize or Hamper the Final Agreement

Articles 74(3) and 83(3) of UNCLOS are central to energy disputes.

While a maritime boundary is unresolved, States must make every effort to negotiate practical provisional arrangements.

The obligation is particularly relevant where one State wishes to:

issue a petroleum licence;

commence drilling;

undertake major construction;

authorize offshore wind development;

conduct seismic exploration; or

develop an offshore energy field.

The Guyana/Suriname arbitration and Ghana/Côte d'Ivoire proceedings demonstrate the practical importance of this principle. (PCA CPA)

12. Environmental Considerations

Modern offshore energy disputes increasingly involve environmental obligations.

Large-scale offshore petroleum projects can affect:

marine ecosystems;

fisheries;

coastal communities;

migratory species;

pollution levels; and

marine biodiversity.

Consequently, maritime boundary disputes can overlap with obligations concerning prevention of marine pollution and environmental impact assessment.

A State cannot necessarily treat the disputed maritime zone as an area free from international environmental obligations merely because it asserts sovereignty over it.

13. Relationship with Investment Arbitration

Maritime boundary disputes can also produce international investment disputes.

For example, an energy company may receive a petroleum concession from State A. State B subsequently establishes that part of the concession falls within State B's maritime jurisdiction.

The company may then face:

cancellation of its licence;

suspension of exploration;

inability to recover investment;

regulatory uncertainty; or

competing claims from governmental authorities.

Investment treaties may become relevant depending on:

nationality of the investor;

applicable treaty;

existence of a protected investment;

jurisdictional requirements; and

the precise governmental conduct involved.

Thus, maritime boundary uncertainty can become an important form of political and regulatory risk in international energy investment.

14. Major Case Laws at a Glance

15. Key Legal Principles

The case law establishes several important principles:

1. Maritime boundaries determine energy jurisdiction

The State possessing maritime jurisdiction generally obtains the corresponding sovereign rights over offshore natural resources.

2. Petroleum concessions do not automatically establish boundaries

A unilateral concession cannot by itself create an international maritime boundary.

3. State practice can be evidentially relevant

Consistent, mutual and long-standing oil and gas practice may sometimes constitute a relevant circumstance.

4. Pending disputes require restraint

States should avoid activities that jeopardize or hamper the final delimitation process.

5. Provisional arrangements are important

Joint development and other practical arrangements can permit resource management while sovereignty remains unresolved.

6. Courts focus on equitable delimitation

The objective is not simply to maximize a State's access to hydrocarbons but to establish a legally justified maritime boundary.

7. Energy companies bear significant boundary risk

A petroleum licence issued under domestic law does not guarantee internationally recognized title to an offshore resource.

Conclusion

International maritime boundary energy disputes represent a major intersection between international law of the sea and international energy law. The legal significance of these disputes extends beyond drawing a line on a map: the boundary determines access to petroleum, natural gas, offshore renewable energy and other seabed resources.

The most important authorities—including Tunisia/Libya, Guyana/Suriname, Romania/Ukraine, Ghana/Côte d'Ivoire and Somalia/Kenya—show that international tribunals carefully distinguish between the legal delimitation of maritime zones and the economic activities occurring within those zones.

The central lesson is that offshore energy development should not be treated as a substitute for maritime delimitation. Where boundaries are uncertain, States are expected to negotiate in good faith, avoid conduct that prejudices the eventual settlement, and consider practical provisional arrangements. Petroleum concessions and historical resource activities may provide evidence relevant to delimitation, but they do not ordinarily determine sovereignty by themselves.

Consequently, effective international energy governance requires coordination between UNCLOS maritime delimitation rules, petroleum licensing systems, environmental obligations, investment protection and dispute-settlement mechanisms. The growing importance of offshore oil, gas and renewable energy makes these principles increasingly significant for international energy law.