China's "U-shaped Line" in the South China Sea

China’s claims to the disputed islands in the South China Sea and their inclusion on a map that depicts a U-shaped line that comes perilously close to the coastal waters of the countries that abut the sea, have given rise to concern and debate about the line’s meaning. At stake are billions of dollars in fishing and mineral rights that all of the parties to the debate each claim as their own.

Although the dispute over the Paracels started as long ago as 1909 between China and colonial Vietnam, then represented by France, and that over the Spratlys started in the 1930s between France and Japan, the arguments over the maritime space beyond 12 nautical miles from these islands are relatively recent.

In the 1960s Indonesia and Malaysia began to make claims to the continental shelf in the southern part of the South China Sea and in 1969 the two countries signed a demarcation agreement. In 1971 the then Republic of Vietnam, i.e., South Vietnam, declared a continental shelf claim that overlapped with those of Malaysia and Indonesia.

China -- that is, the pre-1949 Kuomintang government -- advanced a claim to the Spratlys from the end of the Second World War, and published a map in 1948 showing the now-well-known U-shaped line. Although the area inside that line overlaps the continental shelf claims of Indonesia, Malaysia and South Vietnam, neither the People's Republic of China in Beijing nor the Nationalists now camped in Taipei objected to these claims, nor to the 1969 Indonesia-Malaysia agreement, nor did they advance any claims of their own.

In the 1990s, however, the government in Beijing started to protest against Vietnam’s oil and gas activities in the Nam Con Son and Vanguard Bank areas, and in 1992 it awarded an area of 25,000 sq km in the Vanguard Bank area to a US company. Since then, China’s words and actions in claiming maritime space far beyond 12 nautical miles from the disputed islands have been increasingly assertive.

In this context, China’s inclusion of a map that depicts the U-shaped line in unsigned diplomatic notes sent to the Commission on The Limit of the Continental Shelf in 2009, without explanation of the line’s meaning, has given rise to much discussion. Experts and diplomats ponder what China intends to claim inside that line and how China might use that line to support its claims.

Four potential meanings of the U-shaped line have been advanced and will be considered here.


  1. China’s Foreign Ministry has stated that China claims the islands inside the U-shaped line. By international law, this would include the 12-nautical-mile territorial sea and any EXCLUSIVE ZONE and continental shelf that these islands generate. If this is all what China is claiming, with no implication that this line represents a claim to rights over maritime space right up to it, then this would be the most reasonable and legally valid interpretation of the U-shaped line. If the U-shaped line represents such claims, it is no more controversial than the claims to islands by other states. However, China has not stated that this is all what the U-shaped line represents.

  2. The government of the Republic of China (i.e., the Taiwan authorities), which is not recognized as a sovereign state, has described the area inside the U-shaped line as historical waters. This view is shared by some mainland scholars. However, international law has never recognized claims of historical waters that extend so far out to sea and cover such a vast area. In any case, there is no evidence that China has historically exercised sovereignty over the area enclosed by the U-shaped line. Therefore the interpretation of the area inside the U-shaped line as historical waters is overwhelmingly rejected by international law and evidence. Furthermore, given that historical waters are normally enclosed by baselines rather than lie outside them, such interpretation would be inconsistent with baseline declarations made by the PRC.

  3. China’s diplomatic note to the CLCS in 2009 in relation to Vietnam and Malaysia’s unilateral and joint CLCS submissions claim sovereignty over the “adjacent waters” of the islands in the South China Sea and sovereign rights and jurisdiction over “relevant waters as well as the seabed and subsoil thereof”, referring to a map on which the U-shaped line is depicted, but without declaring that this line demarcates any of these areas. In 2011, China submitted a further asserting that “China’s Nansha Islands is fully entitled to Territorial Sea, Exclusive Economic Zones and Continental Shelf”. These notes seem to support a third interpretation: that China intends to claim the area inside the U-shaped line as an exclusive zone and continental shelf generated by the disputed Paracels, Spratlys and Scarborough Reef. However, while this is a possible speculation, there has been no official statement from China to confirm it. Further, given that the U-shaped line for the most part lies closer to undisputed territories than to the disputed Paracels, Spratlys and Scarborough Reef, it would be impossible for China to justify it as a boundary for the exclusive zone and continental shelf generated by these features.

  4. Since China is not ready to settle for the first interpretation, and since the second and third are clearly indefensible under international law, in recent years Chinese scholars have advanced a fourth interpretation. According to this interpretation, China’s claims in the South China Sea are composed of three layers. In the first, China claims the disputed islands. In the second, it claims the exclusive zone and continental shelf generated by those islands, which might not extend as far as the U-shaped line. In the third layer, China claims “historic rights” over maritime space beyond 12 nautical miles from the islands, with the U-shaped line being either the limit or both the basis and the limit for this claim.

Historic rights derived from the U-shaped line?

The second and fourth interpretations differ in this respect: in the latter interpretation, the proponents do not claim that the “historic rights” in the third layer mean historic sovereignty, or that the area enclosed by the U-shaped line is historic waters. Instead, the proponents of this interpretation suggest that these “historic rights” are not absolute or exclusive, but entail the right to a share, perhaps even a preferential one, of the resources right up to the U-shaped line, even where the exclusive zone and continental shelf of the disputed islands fall short of this line.

By taking a step back from claiming historical water status and absolute sovereignty for the entire area enclosed by the U-shaped line, the proponents of the fourth interpretation appear to hope to avoid the indefensibility of the second interpretation, while allowing China to claim a share to the resources right up to the U-shaped line, something that would not be possible with the first interpretation.

For this fourth interpretation, i.e., the “historic rights” argument, to be valid, two conditions must be satisfied. First, China must have legally acquired historic rights over the maritime space beyond 12 nautical miles from the disputed features prior to the existence of the United Nations Convention on the Law of the Sea. Second, these historic rights must be of the types that are preserved by that convention.

Although the U-shaped line first appeared on its official maps in 1948, China has never declared that that line represents a claim to rights over maritime space for the area enclosed. In recent years, Beijing has studiously ignored calls on it to “clarify its claim.”

To date, therefore, the U-shaped line remains a line on the map with unspecified meaning and has never been officially advanced as a claim to rights over maritime space for the area enclosed. No rights over maritime space for the area enclosed, whether pre-UNCLOS or not, can be derived from a line that has never become a claim to such rights.

Even if, hypothetically, in 1948 China had declared that the U-shaped line represented a claim to rights over maritime space, that line lies too far from the disputed islands to be a legitimate claim to rights over maritime space under the law of the sea at that time. That line, therefore, could never have become a legitimate claim over maritime space, and it has never been recognized as such by any country.

What about other sources of historic rights?

If not the U-shaped line, then, can traditional fishing activities by Chinese fishermen be the basis for claims to historic rights over maritime space? It should be note that Chinese fishermen were by no means the only fishermen who traditionally fished in the South China Sea. Therefore, even if some historic rights could be derived from traditional fishing activities, China would not have a monopoly of these rights.

Additionally, in a case concerning the continental shelf of Libya and Tunisia, the International Court of Justice ruled that historic rights derived from traditional fishing activities stemmed from a legal regime distinct from that of the continental shelf and were not relevant. Therefore, while traditional fishing activities by the peoples around the South China Sea might give rise to a common fishing area through a political settlement, they do not provide the basis for claims against the continental shelf.

Can any other declarations or actions by China be the legal basis for claims to historic rights over maritime space? In practice, when Indonesia and Malaysia made claims to the continental shelf in the southern part of the South China Sea in the 1960s, when they signed a demarcation agreement in 1969, and when South Vietnam made a claim in this area in 1971, China did not protest these actions. It was not until the 1990s that China made its own claim to the continental shelf in this area. Therefore, in the southern part of the South China Sea, if anything, Indonesia, Malaysia and Vietnam have pre-UNCLOS rights over the continental shelf beyond 12 nautical miles from the disputed islands, while China does not.

The most legally valid interpretation

Therefore, while it is true that some rights that a country acquired prior to UNCLOS over the maritime space between 12 and 200 nautical miles from its territory might affect the post-UNCLOS delimitation of areas of overlapping entitlements, this consideration is moot because it is highly questionable that China ever acquired such rights in the first place.

In conclusion, none of the three interpretations of the U-shape line as the basis or limit to claims to rights over the entire maritime space enclosed by it, namely, as a claim to historical waters, a claim to the exclusive zone and continental shelf, or a claim to historic rights over resources, has sufficient legal basis. The most legally valid and reasonable interpretation of the U-shaped line remains that of a claim only to the islands within that line.

The basis and extent of any subsequent claim to rights over maritime space should then be derived from the islands using UNCLOS and the international courts’ past rulings on maritime delimitation, and not from the U-shaped line.

(Duong Danh Huy is a physicist and resident of the United Kingdom whose whose avocation is international maritime law.)