The maritime boundary between China and Vietnam consists of a 273 nautical mile long line that extends from the land boundary terminus in the Gulf of Tonkin (or Bac Bo or Beibu Gulf) to the more southerly entrance into the South China Sea. The boundary was established by agreement in 2000 along with a companion agreement that created a Common Fishing Zone. The Parties’ overlapping entitlements were delimited using the equidistance methodology but modified to produce a more equitable outcome. As a result, each State received a share of the Gulf that is roughly equal to the length of their relevant coasts.

Beyond the Gulf of Tonkin, the shared maritime space of the two States extends into the waters of the hotly disputed South China Sea, or East Sea as it is known in Vietnam. A significant portion of China’s and Vietnam’s claims in the South China Sea overlap, which has been a source of tension between the two States. Both States occupy features in the South China Sea claimed by the other, as well as by additional littoral States in the region.

China and Vietnam are in talks about establishing their maritime boundary beyond the Gulf of Tonkin but have not yet resolved any of the issues in dispute.