Introduction

The extraction of hydrocarbons from beneath the seabed has remained one of the principal drivers of maritime law development since the twentieth century. The legal architecture surrounding offshore oil and gas is not contained in a single instrument. Rather, it consists of a complex interaction among treaty obligations, customary international law, national legislation, contractual arrangements, environmental standards, and judicial decisions. At the center of this framework stands the United Nations Convention on the Law of the Sea (UNCLOS), adopted in 1982 and in force since 1994.

UNCLOS is frequently described as the constitutional framework of the oceans because it establishes a comprehensive allocation of maritime rights and jurisdiction. With respect to offshore hydrocarbons, however, the legal structure is more complicated than a simple territorial division. Petroleum resources may be located beneath the seabed in the territorial sea, exclusive economic zone (EEZ), continental shelf, or, in exceptional geological circumstances, beneath areas of extended continental shelf beyond 200 nautical miles.

The fundamental legal principle is that coastal States possess sovereign rights, rather than full sovereignty, over the continental shelf for the purpose of exploring it and exploiting its natural resources. These rights are exclusive and exist ipso facto and ab initio, meaning that they do not depend upon occupation, proclamation, or actual exploitation.

At the same time, offshore petroleum activities can produce significant environmental risks. Drilling, seismic exploration, pipeline construction, offshore platforms, production operations, and decommissioning may affect marine ecosystems, fisheries, navigation, neighboring States, and the global climate system.

The contemporary legal regime must therefore reconcile several interests:

• coastal-State resource sovereignty;

• freedom of navigation;

• rights of neighboring States;

• maritime delimitation;

• environmental protection;

• prevention of transboundary harm;

• energy security;

• investment and economic development; and

• increasingly, climate-related obligations.

This article examines these issues through the framework of UNCLOS and related international law. It considers the legal basis of offshore petroleum rights, the continental shelf regime, outer-limit determination, maritime delimitation, disputed areas, transboundary hydrocarbon deposits, environmental obligations, offshore installations, pipelines, liability, decommissioning, and the emerging relationship between offshore hydrocarbons and international climate law.

1. What Rights Does a Coastal State Have over the Seabed?

The starting point for any analysis of offshore hydrocarbons is the distinction between the exclusive economic zone and the continental shelf, even though these regimes frequently overlap geographically.

Article 56 of UNCLOS grants the coastal State sovereign rights for the purpose of exploring, exploiting, conserving, and managing the natural resources of the waters superjacent to the seabed and of the seabed and its subsoil within the EEZ.

The continental shelf regime is established principally by Articles 76–85.

Article 77 provides that the coastal State exercises sovereign rights over the continental shelf for the purpose of exploring it and exploiting its natural resources.

These rights are:

1. exclusive;

2. functional; and

3. directed principally toward resource exploration and exploitation.

They are therefore different from sovereignty over land territory.

A coastal State does not acquire complete sovereignty over the continental shelf merely because it possesses sovereign rights over its resources.

2. Sovereignty and Sovereign Rights

The distinction between sovereignty and sovereign rights is fundamental.

Within its territorial sea, a coastal State generally exercises sovereignty, subject to the applicable rules of international law, including innocent passage.

Within the continental shelf, by contrast, the coastal State possesses sovereign rights for specified purposes.

This distinction means that other lawful uses of the sea are not automatically extinguished by the existence of petroleum rights.

For example, the continental shelf may simultaneously be subject to:

• navigation;

• submarine cable operations;

• scientific research;

• fishing in the superjacent waters;

• environmental protection; and

• other lawful uses.

The coastal State's petroleum rights therefore exist within a broader international legal framework.

3. The Continental Shelf as a Legal Institution

The continental shelf is one of the most distinctive concepts in modern international law.

Historically, the concept developed from the geological observation that continental land masses continue beneath shallow seas.

The legal significance of this geological relationship was transformed by the 1945 Truman Proclamation, through which the United States asserted jurisdiction and control over the natural resources of its continental shelf.

The proclamation contributed to the rapid development of continental shelf law.

The International Court of Justice subsequently addressed the issue in the North Sea Continental Shelf Cases.

The Court emphasized the relationship between the continental shelf and the coastal State's territory and described continental shelf rights as arising from the principle of natural prolongation.

UNCLOS eventually codified and substantially developed this regime.

4. Natural Prolongation and Modern Continental Shelf Law

The concept of natural prolongation historically played a central role in continental shelf jurisprudence.

In the North Sea Continental Shelf cases, the ICJ emphasized that the continental shelf constituted a natural prolongation of the land territory of the coastal State.

However, subsequent jurisprudence progressively limited the practical importance of geology as the sole determinant of maritime entitlement.

Modern international law distinguishes between:

• entitlement to a continental shelf; and

• delimitation of overlapping continental shelves.

Every coastal State has at least a continental shelf extending to 200 nautical miles where applicable under UNCLOS, regardless of whether its geological continental margin physically reaches that distance.

Beyond 200 nautical miles, geological and geomorphological criteria become relevant under Article 76.

5. The 200-Nautical-Mile Continental Shelf

One of the most important legal developments under UNCLOS is the recognition that a coastal State's continental shelf normally extends at least to 200 nautical miles from its baselines where the outer edge of the continental margin does not extend that far.

This means that a State does not have to demonstrate a geological continental margin reaching 200 nautical miles in order to possess continental shelf rights to that distance.

This creates an important distinction between:

legal entitlement and physical geology.

The 200-nautical-mile continental shelf is primarily a legal entitlement.

Beyond 200 nautical miles, however, the outer continental shelf regime becomes considerably more technical.

6. The Extended Continental Shelf

Article 76 permits a coastal State, under specified conditions, to establish the outer limits of its continental shelf beyond 200 nautical miles.

This requires application of complex geological and geomorphological criteria.

The outer edge of the continental margin may be determined through formulas based upon:

• the outer edge of the continental margin;

• sediment thickness;

• distance from the foot of the continental slope; and

• the 350-nautical-mile constraint and related provisions applicable to the relevant seabed configuration.

The legal process is therefore a combination of:

geology + geography + international law.

7. The Commission on the Limits of the Continental Shelf

The Commission on the Limits of the Continental Shelf (CLCS) plays an important technical role in this process.

A coastal State seeking to establish the outer limits of its continental shelf beyond 200 nautical miles generally submits scientific and technical information to the Commission.

The Commission considers the submission and makes recommendations.

The CLCS is not a court.

It does not determine maritime boundaries between neighboring States.

This distinction is essential.

The Commission addresses the question:

How far may the coastal State establish the outer limit of its continental shelf under Article 76?

It does not ordinarily answer:

Where is the boundary between two States with overlapping entitlements?

That second question is principally one of maritime delimitation.

8. Entitlement Versus Delimitation

The distinction between entitlement and delimitation is one of the central concepts in contemporary maritime jurisprudence.

Entitlement

Determines the maritime area to which a State has a legal claim under international law.

Delimitation

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

These are different legal questions.

Two States may each possess valid continental shelf entitlements extending 200 nautical miles.

Where their coasts are sufficiently close, those entitlements overlap.

The existence of the overlapping entitlement does not itself establish the boundary.

A delimitation agreement or judicial/arbitral determination is required.

9. Maritime Delimitation and Offshore Hydrocarbons

Hydrocarbon deposits frequently make maritime delimitation politically and economically sensitive.

A boundary may determine which State possesses jurisdiction over:

• oil fields;

• gas fields;

• exploration blocks;

• drilling platforms;

• pipelines;

• seismic surveys; and

• revenue streams.

Consequently, maritime boundaries are not merely cartographic lines.

They can determine substantial economic rights.

This explains why offshore oil and gas disputes have been among the most persistent maritime boundary disputes.

10. The Equidistance/Relevant Circumstances Method

Contemporary maritime delimitation jurisprudence has generally moved toward a structured methodology.

For many continental shelf and EEZ disputes, international courts and tribunals have employed a three-stage approach:

Stage One

Construct a provisional equidistance line.

Stage Two

Consider relevant circumstances that may require adjustment of the line.

Stage Three

Conduct a disproportionality check to determine whether the resulting boundary produces a manifestly inequitable result.

The exact methodology depends on the circumstances and the applicable legal framework.

The key principle is that maritime delimitation should produce an equitable solution, as required by UNCLOS.

11. The Role of Geography

Geographical circumstances remain central to delimitation.

Relevant factors may include:

• coastal configuration;

• concavity;

• islands;

• coastal length;

• geographical distortion;

• presence of offshore islands;

• proportionality; and

• the relationship between adjacent or opposite coasts.

However, international courts have generally rejected purely mathematical approaches.

A mechanically calculated equidistance line may produce distortions where a coast is highly irregular.

12. Islands and Offshore Petroleum Rights

Islands can significantly affect offshore petroleum rights.

Under UNCLOS, islands generally generate maritime zones comparable to other land territory, subject to Article 121.

However, the legal effect of an island in maritime delimitation may differ from its theoretical entitlement.

An island may have:

• full effect;

• partial effect; or

• limited effect

in determining the boundary, depending on the circumstances.

Small islands located near a mainland coast or opposite another State's coast can therefore become highly significant in offshore oil and gas disputes.

13. The Chagos and Other Boundary Disputes

Contemporary maritime jurisprudence demonstrates that offshore resource rights cannot always be separated from broader territorial questions.

Where sovereignty over an island or coastal territory is disputed, the question of who possesses offshore petroleum rights may depend upon the prior determination of territorial sovereignty.

This illustrates a fundamental legal principle:

maritime jurisdiction is derivative of territorial title.

A State cannot normally establish maritime zones from territory over which it has no valid sovereignty.

14. Joint Development Zones

Where maritime boundaries remain unresolved, States may establish joint development zones.

Under such arrangements, neighboring States agree to cooperate in exploring and exploiting resources in a disputed or overlapping maritime area.

A joint development agreement may provide for:

• shared exploration;

• joint licensing;

• revenue allocation;

• joint operating companies;

• environmental standards;

• dispute settlement; and

• temporary suspension of final boundary claims.

Joint development can therefore function as a practical alternative to immediate delimitation.

15. Why Joint Development Is Attractive

Joint development has several advantages.

It can:

• reduce political tension;

• permit resource exploitation;

• prevent unilateral drilling;

• establish environmental safeguards;

• create economic incentives for cooperation; and

• preserve the parties' respective legal positions.

However, it can also generate difficulties concerning:

• revenue distribution;

• management;

• taxation;

• liability;

• regulatory authority;

• termination;

• ownership of infrastructure; and

• the eventual maritime boundary.

Joint development therefore requires highly detailed institutional arrangements.

16. Transboundary Hydrocarbon Deposits

One of the most difficult offshore petroleum problems arises when a single oil or gas reservoir extends across a maritime boundary.

The geological structure does not necessarily follow the legal boundary.

A reservoir may physically extend beneath:

• State A's continental shelf; and

• State B's continental shelf.

Uncoordinated exploitation may cause pressure changes affecting the resource on the other side of the boundary.

This creates a classic transboundary resource problem.

17. The Principle of Cooperation over Shared Deposits

International law increasingly favors cooperation where a petroleum deposit straddles an international boundary.

States may negotiate:

• unitization agreements;

• joint operating arrangements;

• information-sharing procedures;

• production-sharing formulas;

• reservoir-management plans; and

• environmental standards.

The objective is to prevent the legal boundary from encouraging inefficient or environmentally harmful exploitation.

18. Unitization

Unitization is a particularly important mechanism.

Under unitization, a transboundary petroleum reservoir is treated as a single geological field for purposes of development.

The parties agree on:

• reservoir boundaries;

• production rates;

• development plans;

• ownership shares;

• operatorship;

• costs;

• revenues;

• monitoring; and

• dispute settlement.

Unitization is based on the recognition that geological unity may require legal and operational cooperation.

19. Unilateral Drilling in Disputed Areas

A particularly sensitive situation arises when one State authorizes drilling in an area claimed by another State.

Such conduct may escalate a maritime boundary dispute.

The legal assessment depends on whether:

• a final boundary exists;

• provisional arrangements have been negotiated;

• the area is genuinely disputed;

• the activity risks permanent prejudice;

• the drilling creates environmental risks; and

• applicable dispute-settlement obligations exist.

International jurisprudence has emphasized that States involved in delimitation disputes should avoid actions that aggravate the dispute or compromise the eventual implementation of the boundary.

20. Provisional Arrangements Pending Delimitation

Article 83 of UNCLOS is particularly important for continental shelf delimitation.

Where States have overlapping claims, they are required to seek agreement on provisional arrangements of a practical nature and, during the transitional period, make every effort not to jeopardize or hamper the reaching of a final agreement.

This provision creates an important legal expectation of restraint.

In petroleum disputes, provisional arrangements may involve:

• moratoria on drilling;

• joint development;

• notification mechanisms;

• shared environmental monitoring;

• data exchange; or

• temporary licensing arrangements.

21. Offshore Exploration

Offshore petroleum development generally occurs through several stages.

Stage One: Geological and seismic exploration

Companies conduct seismic surveys to identify possible hydrocarbon structures.

Stage Two: Exploratory drilling

A well is drilled to determine whether commercially recoverable hydrocarbons exist.

Stage Three: Appraisal

Additional drilling determines the size and characteristics of the reservoir.

Stage Four: Development

Production platforms, subsea systems, pipelines, and other infrastructure are constructed.

Stage Five: Production

Oil and gas are extracted and transported.

Stage Six: Decommissioning

The infrastructure is eventually removed, abandoned, or otherwise managed according to applicable law.

Each stage raises distinct legal questions.

22. Seismic Exploration and Environmental Regulation

Seismic surveys use powerful acoustic signals to identify geological structures beneath the seabed.

These activities may affect marine organisms, particularly species sensitive to underwater sound.

The environmental regulation of seismic exploration may therefore involve:

• environmental impact assessment;

• protected species;

• seasonal restrictions;

• exclusion zones;

• monitoring;

• mitigation measures; and

• cumulative-impact assessment.

This illustrates that environmental obligations may apply before any oil or gas is actually extracted.

23. Environmental Impact Assessment

Environmental Impact Assessment (EIA) has become one of the central legal mechanisms governing offshore petroleum activities.

An EIA seeks to identify:

• environmental risks;

• alternative approaches;

• mitigation measures;

• cumulative impacts;

• transboundary effects; and

• monitoring requirements.

Under contemporary international law, environmental impact assessment is increasingly recognized as a general legal requirement where proposed activities may create significant adverse environmental effects in a transboundary context.

The ICJ's jurisprudence, particularly Pulp Mills, contributed significantly to the development of this principle.

The BBNJ Agreement has further developed EIA obligations for activities within its scope in areas beyond national jurisdiction, although its relationship with existing sectoral regimes requires careful analysis.

24. UNCLOS and Marine Environmental Protection

Part XII of UNCLOS establishes extensive obligations concerning the protection and preservation of the marine environment.

Article 192 provides a general obligation for States to protect and preserve the marine environment.

Article 194 requires States to take measures to prevent, reduce, and control pollution of the marine environment from various sources.

These provisions apply alongside the coastal State's resource rights.

This is a fundamental point:

UNCLOS does not treat resource exploitation and environmental protection as legally separate spheres.

A coastal State's sovereign rights to exploit petroleum must be exercised consistently with its international environmental obligations.

25. Pollution from Offshore Installations

Article 194 specifically addresses pollution from installations and devices used in exploration or exploitation of the natural resources of the seabed and its subsoil.

Offshore petroleum operations may generate:

• oil spills;

• produced water;

• drilling waste;

• chemical discharges;

• atmospheric emissions;

• underwater noise;

• seabed disturbance; and

• accidental pollution.

States must therefore adopt appropriate measures to prevent and control such pollution.

This obligation has both a preventive and regulatory character.

26. The Duty of Due Diligence

Modern international environmental law increasingly understands marine environmental obligations through the concept of due diligence.

A State is not necessarily required to guarantee that no environmental harm ever occurs.

Rather, it must take reasonable measures appropriate to the level of risk.

These may include:

• licensing systems;

• technical standards;

• environmental assessments;

• monitoring;

• emergency preparedness;

• contingency planning;

• inspection;

• enforcement; and

• regulatory oversight.

The required level of diligence may increase as the potential environmental risk becomes more serious.

27. Best Available Technology

Offshore petroleum regulation increasingly relies upon technological standards.

States may require operators to employ:

• blowout preventers;

• double-hulled transport systems;

• emergency shutdown systems;

• leak detection;

• spill-response equipment;

• redundant safety systems;

• methane monitoring; and

• advanced well-control technologies.

International law does not necessarily prescribe one universal technological standard.

Instead, states must develop regulatory systems capable of addressing the environmental and safety risks associated with offshore operations.

28. Offshore Platforms and Artificial Islands

Article 60 of UNCLOS provides coastal States with jurisdiction concerning artificial islands, installations, and structures within their EEZ.

The coastal State may establish:

• safety zones;

• construction rules;

• removal requirements; and

• navigational protections.

However, offshore installations do not acquire the status of islands.

They do not generate their own territorial sea, EEZ, or continental shelf.

This prevents a State or private operator from creating additional maritime zones through the construction of an offshore platform.

29. Safety Zones

Safety zones surrounding offshore installations are intended to protect:

• workers;

• vessels;

• installations;

• navigation; and

• the marine environment.

The breadth of such zones is regulated by UNCLOS and relevant international standards.

States must balance safety requirements against the freedom of navigation.

An excessively large or improperly enforced safety zone could interfere unlawfully with international navigation.

30. Submarine Pipelines

Offshore oil and gas development frequently requires pipelines connecting production facilities with coastal terminals or other infrastructure.

UNCLOS recognizes rights concerning submarine cables and pipelines but also preserves the regulatory interests of coastal States.

Within areas under coastal-State jurisdiction, pipeline construction may be subject to national regulation.

The precise legal regime varies according to whether the pipeline is located in:

• territorial sea;

• EEZ;

• continental shelf; or

• high seas.

Environmental assessment and routing decisions may therefore become significant legal issues.

31. Navigation and Offshore Infrastructure

Offshore installations cannot be treated as isolated industrial facilities.

They exist within maritime spaces used by:

• commercial shipping;

• fishing vessels;

• military vessels;

• scientific vessels;

• submarine cables; and

• other maritime users.

The coastal State must therefore coordinate petroleum development with navigation and other lawful uses of the sea.

This is an example of the principle of reasonable accommodation among competing uses of maritime space.

32. Marine Scientific Research and Petroleum Exploration

A distinction must be made between:

• marine scientific research; and

• resource-oriented exploration.

UNCLOS establishes a specific legal regime for marine scientific research.

Commercial seismic surveys and petroleum exploration may fall outside the conventional concept of purely scientific research where their principal objective is the exploration of natural resources.

This distinction can have consequences concerning consent and coastal-State regulation.

33. Offshore Oil and Gas in the High Seas

The legal position changes substantially beyond national jurisdiction.

The high seas are not subject to national sovereignty.

The seabed and subsoil of areas beyond national jurisdiction are governed by the separate legal regime of the Area under Part XI of UNCLOS.

The mineral resources of the Area are designated as the common heritage of mankind.

Consequently, commercial exploitation of oil and gas beneath the seabed of the Area would raise fundamentally different legal questions from petroleum exploitation on a coastal State's continental shelf.

The International Seabed Authority has jurisdiction over mineral resources of the Area.

However, the contemporary regulatory framework for seabed mineral activities is far more developed in relation to polymetallic nodules, sulphides, and cobalt-rich crusts than conventional offshore petroleum.

The distinction between petroleum under a national continental shelf and resources in the Area remains legally fundamental.

34. Hydrocarbons and the Common Heritage of Mankind

It is important not to assume that all offshore hydrocarbons are subject to the common-heritage principle.

The principle applies to the resources of the Area, as defined in UNCLOS.

Petroleum located beneath a coastal State's continental shelf is not transformed into a common-heritage resource merely because it lies beneath the seabed.

The coastal State possesses sovereign rights over such resources.

This distinction is essential when analyzing offshore drilling projects.

35. Transboundary Environmental Harm

Offshore petroleum activities may cause environmental effects extending beyond national jurisdiction.

An oil spill may move across maritime boundaries.

Air pollution may affect neighboring States.

A major accident may damage fisheries or ecosystems beyond the area of the original activity.

International law therefore imposes obligations concerning the prevention of transboundary harm.

States must exercise due diligence to ensure that activities under their jurisdiction or control do not cause significant environmental damage to other States or to areas beyond national jurisdiction.

36. The No-Harm Principle

The no-harm principle is an important component of contemporary international environmental law.

It does not necessarily establish absolute liability for every environmental consequence.

Rather, it requires States to take appropriate preventive measures where activities under their jurisdiction create a foreseeable risk of significant transboundary environmental harm.

In offshore petroleum operations, this principle supports:

• environmental assessment;

• emergency planning;

• monitoring;

• information exchange;

• notification; and

• cooperation.

37. Emergency Notification and Cooperation

Oil spills and blowouts can develop rapidly.

International law therefore increasingly emphasizes cooperation during environmental emergencies.

States should maintain mechanisms for:

• early warning;

• notification;

• exchange of information;

• emergency response;

• technical cooperation; and

• assistance.

Regional marine-environmental agreements can supplement UNCLOS by establishing more detailed response procedures.

38. Liability for Offshore Oil Pollution

Liability is another important component of offshore petroleum regulation.

Potential liability may arise from:

• pollution damage;

• personal injury;

• property damage;

• fisheries losses;

• environmental restoration;

• transboundary harm; and

• costs of emergency response.

The applicable liability regime depends upon the type of activity, location, national law, contractual arrangements, and applicable international conventions.

A major difficulty is determining whether liability should be:

• based upon fault;

• strict;

• limited;

• unlimited; or

• distributed among several responsible actors.

39. Operator Liability and State Responsibility

It is essential to distinguish operator liability from international responsibility of the State.

A private petroleum company may be responsible under national law or contract for pollution caused by its operations.

The State may simultaneously incur international responsibility if it failed to exercise appropriate regulatory due diligence.

These two forms of responsibility are legally distinct.

The existence of private liability does not automatically eliminate possible international responsibility.

40. Decommissioning Offshore Installations

An offshore petroleum project does not end when production stops.

Decommissioning may involve:

• removing platforms;

• plugging wells;

• removing pipelines;

• leaving subsea infrastructure in place;

• restoring the seabed;

• managing contaminated material; and

• monitoring abandoned structures.

International law therefore increasingly treats decommissioning as part of the overall life cycle of offshore development.

UNCLOS Article 60 requires abandoned or disused installations and structures to be removed, taking into account generally accepted international standards.

41. Abandoned Installations and Marine Hazards

Leaving an offshore platform in place may create:

• navigational hazards;

• pollution risks;

• habitat impacts;

• fishing interference; or

• structural deterioration.

However, complete removal may itself cause environmental damage.

This creates a difficult legal and scientific question:

Should an installation always be removed, or can leaving part of it in place sometimes be environmentally preferable?

The answer requires consideration of:

• navigational safety;

• environmental effects;

• technical feasibility;

• cost;

• ecological value; and

• international standards.

42. Offshore Petroleum and Climate Change

The most significant emerging issue is the relationship between offshore hydrocarbons and climate change.

Oil and gas production contributes to greenhouse-gas emissions through:

• combustion;

• methane leakage;

• flaring;

• venting;

• transportation;

• processing; and

• associated energy consumption.

The Paris Agreement and evolving international climate law increasingly influence the legal environment in which petroleum development occurs.

The central question is no longer simply:

Does a State possess the legal right to extract hydrocarbons?

It increasingly becomes:

How must that right be exercised consistently with environmental and climate obligations?

43. Climate Change and the Law of the Sea

The interaction between UNCLOS and climate change has become an increasingly important field of international legal development.

The ITLOS Advisory Opinion on Climate Change and International Law, delivered in 2024 in response to a request by the Commission of Small Island States, significantly clarified that States have obligations under UNCLOS concerning marine pollution caused by anthropogenic greenhouse-gas emissions.

This development is important for offshore petroleum law.

Greenhouse-gas emissions are now increasingly considered within the broader framework of marine environmental obligations.

44. Offshore Oil and Gas after the ITLOS Climate Advisory Opinion

The 2024 ITLOS Advisory Opinion strengthens the argument that climate change cannot be treated as legally external to the law of the sea.

States exercising offshore petroleum activities must therefore increasingly consider:

• greenhouse-gas emissions;

• methane;

• cumulative environmental effects;

• climate impacts on marine ecosystems;

• environmental assessment;

• precaution; and

• mitigation.

The exact legal consequences for individual drilling projects will depend upon the applicable legal framework and the circumstances of the project.

Nevertheless, the jurisprudential direction is significant.

45. Environmental Impact Assessment and Climate Effects

Future offshore petroleum EIAs are likely to increasingly consider not only local pollution but also:

• greenhouse-gas emissions;

• methane leakage;

• cumulative emissions;

• ecosystem effects;

• climate-related risks;

• alternatives;

• decommissioning emissions; and

• downstream consequences.

This may gradually transform the EIA from a primarily local environmental tool into a broader instrument of climate-sensitive decision-making.

46. Cumulative Impacts

A major limitation of project-by-project regulation is that individual petroleum projects may appear environmentally manageable when assessed separately.

The cumulative effect of dozens of projects may be substantially different.

Cumulative impacts can arise from:

• multiple drilling platforms;

• seismic surveys;

• pipelines;

• shipping;

• fishing;

• coastal infrastructure;

• spills;

• underwater noise; and

• greenhouse-gas emissions.

International environmental law is increasingly recognizing the importance of assessing such cumulative effects.

47. Offshore Petroleum and Marine Biodiversity

Petroleum development can affect marine biodiversity through:

• seabed disturbance;

• drilling discharges;

• chemical pollution;

• underwater noise;

• habitat fragmentation;

• vessel traffic;

• accidental spills; and

• infrastructure placement.

The development of the BBNJ Agreement adds another layer to this legal framework for activities within ABNJ.

The challenge will be to ensure that sectoral petroleum regulation and biodiversity governance operate coherently rather than in separate institutional silos.

48. Offshore Petroleum in Disputed Maritime Areas

Petroleum exploration in disputed waters presents one of the most difficult legal situations.

The central legal questions include:

1. Who possesses title to the maritime area?

2. Has a maritime boundary been established?

3. Do the parties have overlapping continental shelf claims?

4. Has a provisional arrangement been concluded?

5. Does drilling risk prejudicing the final settlement?

6. Are environmental risks significant?

7. What dispute-settlement mechanism is available?

A unilateral licensing decision does not necessarily resolve any of these questions.

49. Licensing in Disputed Areas

States sometimes issue petroleum licenses in areas claimed by another State.

Such licensing can have different legal consequences depending on the circumstances.

A license may:

• create commercial expectations;

• encourage investment;

• complicate future negotiations;

• create environmental risks; and

• generate diplomatic disputes.

International law generally favors restraint where unilateral activities could aggravate or prejudice a pending delimitation dispute.

50. Petroleum Agreements and International Law

Offshore petroleum projects are often governed through detailed domestic and contractual arrangements.

Common contractual models include:

• concession agreements;

• production-sharing contracts;

• service contracts;

• joint ventures; and

• risk-service agreements.

These contracts govern issues such as:

• exploration rights;

• production;

• taxation;

• royalties;

• ownership;

• cost recovery;

• local content;

• environmental obligations;

• decommissioning; and

• dispute settlement.

However, a domestic petroleum contract cannot override the State's international obligations.

International law remains the external legal framework within which national petroleum arrangements operate.

51. Investment Law and Offshore Petroleum

Offshore petroleum projects frequently involve substantial foreign investment.

Investors may therefore invoke:

• bilateral investment treaties;

• multilateral investment agreements;

• stabilization clauses;

• arbitration provisions; and

• contractual protections.

Environmental regulation can consequently intersect with international investment law.

A State may possess the sovereign right to strengthen environmental regulation, but disputes can arise where investors argue that regulatory changes violate treaty protections.

The modern challenge is to reconcile:

regulatory sovereignty + environmental protection + investment protection.

52. Energy Security and International Law

Offshore petroleum also has a strategic dimension.

States may consider offshore resources important for:

• energy security;

• national revenue;

• economic development;

• energy independence;

• export earnings; and

• regional stability.

These interests do not eliminate environmental obligations.

Instead, they form part of the broader policy context within which international law is applied.

53. The Principle of Sustainable Development

The concept of sustainable development provides an important bridge between economic and environmental interests.

Offshore petroleum development may generate:

• employment;

• infrastructure;

• government revenue;

• energy supply; and

• technological development.

At the same time, it can generate:

• environmental risks;

• greenhouse-gas emissions;

• biodiversity loss; and

• long-term decommissioning liabilities.

Sustainable development seeks to ensure that economic development is pursued without disregarding environmental protection and the interests of future generations.

54. The Precautionary Principle

The precautionary principle is increasingly relevant to offshore petroleum regulation.

Where there is a risk of serious environmental damage but scientific certainty is incomplete, the absence of complete scientific knowledge should not automatically justify unrestricted activity.

This principle can influence:

• seismic exploration;

• drilling;

• deepwater development;

• Arctic petroleum operations;

• spill-response planning; and

• biodiversity protection.

Its precise legal status varies according to the relevant treaty and jurisdiction, but it has become a significant component of international environmental governance.

55. Arctic Offshore Hydrocarbons

The Arctic presents particularly complex legal conditions.

Offshore petroleum operations in the Arctic involve:

• fragile ecosystems;

• extreme weather;

• ice conditions;

• indigenous communities;

• maritime boundary questions;

• search-and-rescue challenges;

• pollution-response difficulties; and

• rapidly changing climatic conditions.

The Arctic demonstrates how offshore petroleum law intersects with:

• maritime law;

• environmental law;

• indigenous rights;

• climate law; and

• regional cooperation.

56. Deepwater Petroleum

Deepwater drilling presents additional legal and technical risks.

As drilling depth increases:

• pressure increases;

• temperature conditions become more complex;

• emergency response becomes more difficult;

• spill containment becomes harder;

• infrastructure becomes more expensive.

The legal obligation of due diligence must therefore be informed by the actual level of risk.

A regulatory regime appropriate for shallow-water operations may not satisfy the requirements of a deepwater project.

57. Offshore Petroleum and the Duty to Cooperate

Cooperation is increasingly important throughout the petroleum life cycle.

Neighboring States may need to cooperate concerning:

• shared reservoirs;

• pollution emergencies;

• environmental monitoring;

• maritime boundaries;

• pipelines;

• navigation;

• fisheries;

• scientific information; and

• climate impacts.

UNCLOS therefore should not be understood merely as a system allocating exclusive rights.

It also creates a framework for coexistence and cooperation among competing maritime interests.

58. The Emerging Principle of Integrated Ocean Governance

Offshore petroleum law demonstrates the broader transformation of maritime governance.

A petroleum platform may simultaneously implicate:

• continental shelf law;

• EEZ law;

• maritime delimitation;

• environmental law;

• shipping law;

• fisheries law;

• investment law;

• climate law;

• biodiversity law; and

• national petroleum regulation.

No single legal regime can therefore provide the complete answer.

The future of offshore petroleum regulation lies increasingly in integrated ocean governance.

59. Key Legal Challenges for the Future

Several challenges will define the future of offshore oil and gas law.

1. Climate change

How should offshore petroleum rights interact with increasingly stringent climate obligations?

2. Maritime boundary disputes

How should States manage valuable deposits before final delimitation?

3. Environmental risk

What level of due diligence is required for high-risk deepwater operations?

4. Transboundary deposits

How should reservoirs crossing maritime boundaries be developed?

5. Decommissioning

Who bears long-term responsibility for abandoned infrastructure?

6. Biodiversity

How should petroleum development coexist with marine protected areas and ecosystem conservation?

7. Investment

How should environmental regulation interact with investor protections?

60. A Functional Model of Offshore Petroleum Governance

The legal life cycle of an offshore petroleum project can be represented as follows:

Maritime Entitlement → Delimitation → Licensing → Environmental Assessment → Exploration → Drilling → Development → Production → Transportation → Monitoring → Decommissioning

At every stage, international law imposes different constraints.

This demonstrates why offshore petroleum law cannot be reduced to the simple question of who owns the oil.

The legal question is instead:

Who possesses the right to exploit, under what jurisdiction, subject to which environmental standards, through which procedures, and with what obligations toward other States and the international community?

Conclusion

The legal regulation of offshore oil and gas reflects one of the most significant transformations in modern international law.

The early development of continental shelf law was driven largely by the desire of coastal States to secure access to valuable seabed resources. The concept of natural prolongation and the development of continental shelf doctrine established the legal foundation for offshore petroleum rights.

UNCLOS subsequently transformed this historical development into a comprehensive legal regime.

Under contemporary international law, coastal States possess sovereign rights over the continental shelf for the purpose of exploring and exploiting its natural resources. These rights are exclusive but are not equivalent to unrestricted territorial sovereignty. They coexist with navigation rights, environmental obligations, scientific interests, and the rights of other States.

The legal distinction between the continental shelf and the EEZ is particularly important. Petroleum resources beneath the seabed are principally governed by the continental shelf regime, while the superjacent waters may simultaneously be subject to the EEZ regime.

Beyond 200 nautical miles, the legal and scientific complexity increases because coastal States must establish the outer limits of their continental shelf in accordance with Article 76, with the technical involvement of the Commission on the Limits of the Continental Shelf.

Where maritime claims overlap, however, the question shifts from entitlement to delimitation.

International jurisprudence has increasingly developed structured methods for resolving such disputes, while Article 83 of UNCLOS encourages States to negotiate provisional arrangements and refrain from conduct that would jeopardize or hamper the achievement of a final agreement.

This is particularly important for offshore hydrocarbons because petroleum deposits do not follow political boundaries.

Where a reservoir crosses a maritime boundary, cooperation, unitization, and joint development may provide more effective solutions than unilateral exploitation.

At the same time, the environmental dimension of offshore petroleum law has become increasingly important.

Part XII of UNCLOS imposes obligations to protect and preserve the marine environment and to prevent, reduce, and control pollution. These obligations increasingly operate through due diligence, environmental impact assessment, scientific monitoring, emergency preparedness, and technological standards.

The development of international climate law has added another dimension.

The 2024 ITLOS Advisory Opinion on climate change and international law demonstrates the growing interaction between climate obligations and the law of the sea. Greenhouse-gas emissions are increasingly understood within the broader framework of marine environmental protection.

Consequently, offshore petroleum law is undergoing a conceptual transformation.

The central legal question is no longer simply whether a coastal State possesses the right to exploit hydrocarbons.

It is increasingly whether that right can be exercised in a manner consistent with maritime boundaries, environmental protection, climate obligations, scientific uncertainty, the rights of neighboring States, and the interests of future generations.

The future of offshore petroleum law will therefore depend upon the reconciliation of three historically distinct legal objectives:

resource sovereignty, international cooperation, and environmental responsibility.

UNCLOS provides the foundational framework for that reconciliation, but its implementation increasingly depends upon complementary developments in international environmental law, climate law, investment law, regional agreements, judicial jurisprudence, and national regulatory systems.

The resulting legal order is neither one of unrestricted coastal-State exploitation nor one of absolute prohibition.

It is a system in which the right to exploit marine resources is increasingly understood as a regulated sovereign right—one accompanied by duties of prevention, cooperation, due diligence, environmental assessment, and long-term stewardship of the marine environment.

Selected References

1. United Nations Convention on the Law of the Sea, 1982.

2. Vienna Convention on the Law of Treaties, 1969.

3. International Court of Justice, North Sea Continental Shelf Cases (Federal Republic of Germany/Denmark; Federal Republic of Germany/Netherlands), Judgment, 1969.

4. International Court of Justice, Continental Shelf (Libyan Arab Jamahiriya/Malta), Judgment, 1985.

5. International Court of Justice, Maritime Delimitation in the Black Sea (Romania v. Ukraine), Judgment, 2009.

6. International Court of Justice, Maritime Delimitation in the Caribbean Sea and the Pacific Ocean (Costa Rica v. Nicaragua) and related cases.

7. International Court of Justice, Pulp Mills on the River Uruguay (Argentina v. Uruguay), Judgment, 2010.

8. International Court of Justice, Certain Activities Carried Out by Nicaragua in the Border Area (Costa Rica v. Nicaragua), Judgment, 2015.

9. International Tribunal for the Law of the Sea, Responsibilities and Obligations of States Sponsoring Persons and Entities with Respect to Activities in the Area, Advisory Opinion, 2011.

10. International Tribunal for the Law of the Sea, Request for an Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law, Advisory Opinion, 2024.

11. United Nations, Commission on the Limits of the Continental Shelf, Scientific and Technical Guidelines.

12. International Maritime Organization, relevant instruments concerning prevention of pollution and safety of offshore and maritime activities.

13. United Nations Framework Convention on Climate Change, 1992.

14. Paris Agreement, 2015.

15. International Convention for the Prevention of Pollution from Ships (MARPOL), 1973/1978.

16. Convention on Biological Diversity, 1992.

17. Agreement under UNCLOS on the Conservation and Sustainable Use of Marine Biological Diversity of Areas Beyond National Jurisdiction (BBNJ Agreement), 2023.

18. Permanent Court of Arbitration, relevant maritime delimitation and resource-related awards.

19. United Nations, Handbook on the Law of the Sea and relevant Division for Ocean Affairs and the Law of the Sea materials.

20. International Law Commission, relevant work concerning prevention of transboundary harm and allocation of loss in the context of hazardous activities.