Cross-Border Maritime Agreements and Conflicts in the South China Sea

Explore cross-border maritime agreements and ongoing territorial conflicts in the South China Sea. Understand the stakes, legal frameworks, case studies, and what’s at risk for global shipping.”

Why This Topic Matters in Today’s Maritime Landscape

Few regions in the world illustrate the intersection of international trade, geopolitics, and maritime law as sharply as the South China Sea (SCS). This vital waterway carries approximately one-third of the world’s shipping traffic, valued at over $5 trillion USD annually (Council on Foreign Relations, 2024). But beneath the surface of tankers and containerships lies a simmering tension—one that involves contested islands, overlapping Exclusive Economic Zones (EEZs), unresolved claims, and a patchwork of fragile agreements.

For maritime professionals, policymakers, and global logistics players, understanding the legal and political chessboard of the South China Sea is more than academic. It shapes port access, vessel routing, fishing rights, security measures, and the overall cost of trade.

The Legal Foundations: What Governs the Sea?

UNCLOS and the Exclusive Economic Zone Concept

The backbone of maritime governance in the South China Sea is the United Nations Convention on the Law of the Sea (UNCLOS). Ratified by most nations in the region (notably excluding the United States), UNCLOS defines:

  • Territorial waters (up to 12 nautical miles from a nation’s coastline)
  • EEZs (up to 200 nautical miles offshore, granting sovereign rights to marine resources)
  • Continental shelf rights

The challenge in the SCS arises because multiple countries’ EEZs overlap, especially around features like the Spratly Islands, Paracel Islands, Scarborough Shoal, and Natuna Sea.

The 2016 Permanent Court of Arbitration Ruling

A key turning point came in 2016 when the Permanent Court of Arbitration (PCA) ruled in favor of the Philippines in its case against China. The tribunal rejected China’s expansive Nine-Dash Line claim, finding no legal basis for such historical rights.

However, China rejected the ruling, labeling it “null and void.” The outcome intensified friction and raised questions about enforcement in international maritime law, as UNCLOS lacks a police force.

Maritime Agreements: Regional Cooperation vs. Sovereignty Tensions

ASEAN-China Declaration on the Conduct of Parties (DOC)

Signed in 2002, the Declaration on the Conduct of Parties in the South China Sea was an early step toward cooperation between China and the Association of Southeast Asian Nations (ASEAN). It aimed to:

  • Promote peaceful dispute resolution
  • Encourage confidence-building measures
  • Avoid activities that escalate tensions

However, the DOC is non-binding, and critics argue it has not prevented militarization or incidents at sea.

Ongoing Efforts: Code of Conduct (COC)

Negotiations are underway for a legally binding Code of Conduct (COC). As of mid-2025, progress remains slow. Disagreements persist over key clauses:

  • Whether to allow third-party mediation (e.g., the United States)
  • The role of military vessels in EEZs
  • Jurisdiction over fisheries and hydrocarbons

Analysts from WMU Journal of Maritime Affairs suggest a COC, if completed, would likely not resolve territorial claims but could reduce accidental conflict.

Bilateral and Trilateral Agreements

While a multilateral treaty remains elusive, countries have engaged in ad hoc agreements:

  • Philippines and Vietnam: Joint fisheries monitoring and Coast Guard communication channels
  • Malaysia and Brunei: Oil and gas joint development in overlapping zones
  • Indonesia and Vietnam (2022): EEZ boundary agreement in the Natuna Sea, after years of negotiation

These practical partnerships allow resource sharing while sovereignty issues remain in limbo.

Conflict Zones: Who Claims What?

Spratly Islands

Claimed by China, Taiwan, Vietnam, the Philippines, Malaysia, and Brunei, the Spratlys contain over 100 reefs, atolls, and islets—many submerged during high tide. China has constructed military-grade artificial islands on Fiery Cross Reef, Mischief Reef, and Subi Reef.

The result is a triangle of tension:

  • China insists it is defending its territory
  • Vietnam and the Philippines protest militarization
  • International shipping routes pass close by

Paracel Islands

Controlled entirely by China since a naval clash with Vietnam in 1974, the Paracels remain contested. Vietnam claims historical rights, but China maintains a heavy naval presence, including airstrips and radar systems.

Scarborough Shoal

This rich fishing ground is claimed by China, the Philippines, and Taiwan. In 2012, a standoff between Philippine Navy and Chinese maritime vessels resulted in China taking de facto control. Filipino fishermen now report frequent harassment.

Real-World Impacts on Maritime Operations

Threats to Commercial Shipping

While freedom of navigation remains legally protected under UNCLOS, the region has seen:

  • Shadowing by naval vessels
  • Live-fire exercises near commercial sea lanes
  • “Gray zone” harassment by maritime militias

The International Chamber of Shipping (ICS) and BIMCO advise shipowners to maintain high alert and monitor advisories issued via IMO GISIS and Inmarsat Fleet Secure.

Disruption of Fisheries and Local Livelihoods

The SCS supports one of the richest marine ecosystems on the planet, but fish stocks are overexploited and local fishermen are often caught in political crossfire. Vietnamese and Filipino fishers regularly face:

  • Confiscation of gear by foreign patrols
  • Vessel damage
  • Detentions

According to the World Ocean Review, the fishing conflicts are escalating in tandem with ecological degradation.

Offshore Energy Development in Disputed Zones

Hydrocarbons—oil and gas—are central to the SCS dispute. CNOOC (China National Offshore Oil Corporation), Petronas (Malaysia), and Vietnam Oil and Gas Group have all conducted exploratory or commercial drilling. Yet these activities are sometimes interrupted by foreign coast guard ships or diplomatic pressure.

Case Studies in Maritime Conflict and Cooperation

Reed Bank Incident (2019)

A Chinese vessel rammed and sank a Filipino fishing boat near Reed Bank, an area within the Philippines’ EEZ but claimed by China. Although no lives were lost, the incident intensified domestic outrage in the Philippines and raised questions about naval rules of engagement.

Natuna Sea Patrols (2020–2022)

Indonesia launched joint military and coast guard patrols in the North Natuna Sea after repeated incursions by Chinese fishing fleets. While China did not engage militarily, its presence in what Indonesia claims as its EEZ caused regional alarm.

Bilateral Energy Deal: Philippines-China (2018)

In an attempt to ease tensions, Manila and Beijing signed a Memorandum of Understanding (MoU) on joint oil and gas exploration. However, it collapsed in 2022 due to constitutional concerns in the Philippines and lack of clarity over sovereignty.

Challenges in Resolving South China Sea Conflicts

Legal vs. Practical Control

While international law supports EEZs and territorial integrity, “effective control” on the ground (or sea) often determines outcomes. China’s advanced coast guard and naval infrastructure give it operational dominance in many disputed zones.

Lack of Enforcement Mechanisms

Unlike land borders, there is no permanent marine enforcement body. The IMO and UN can offer guidelines, but enforcement is left to sovereign states.

Domestic Politics and Nationalism

Territorial claims are deeply tied to national identity. Leaders often use maritime disputes to bolster domestic support, making compromise politically risky.

Environmental Degradation and Overfishing

The rush to claim territory has led to coral reef destruction, dredging, and resource depletion. Without cooperation, the region’s ecological wealth may vanish.

FAQ: South China Sea Agreements and Conflicts

Q1: Why is the South China Sea so important?
It is a key shipping route, rich in fish and hydrocarbons, and strategically important for military positioning.

Q2: Who claims the South China Sea?
China, the Philippines, Vietnam, Malaysia, Brunei, and Taiwan have overlapping claims. China’s Nine-Dash Line covers nearly the entire sea.

Q3: Is there an international treaty governing this?
UNCLOS is the main framework. A proposed Code of Conduct is being negotiated but not finalized.

Q4: How does this affect global shipping?
Commercial vessels face surveillance, route detours, and higher insurance premiums. Any conflict would disrupt major supply chains.

Q5: What is “gray zone” conflict?
Non-military, coercive actions like using fishing militias or coast guard shadowing to assert territorial control.

Q6: Can UNCLOS be enforced?
It lacks direct enforcement power. Its effectiveness depends on state compliance and diplomatic pressure.

Q7: Are there success stories of cooperation?
Yes. Vietnam and Indonesia’s recent EEZ agreement shows diplomacy can work. Bilateral fisheries agreements have also improved local coordination.

Conclusion: Navigating the Waters of Conflict and Compromise

The South China Sea is more than a geopolitical chessboard—it is a shared sea of commerce, culture, and climate. While disputes dominate headlines, moments of diplomacy and cooperation hint at the possibility of peaceful coexistence.

For maritime professionals, staying informed is not just strategic—it’s essential. Route planning, risk assessment, and operational resilience all depend on understanding the shifting tides of law, power, and negotiation in these contested waters.

The future of the South China Sea may lie in joint development, legal clarity, and multilateral diplomacy, but until then, it remains a region where sovereignty and seafaring collide daily.

References

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