The Beibu Gulf, also the Gulf of Tonkin, is a body of water partially enclosed by northern Vietnam, southern China and China’s Hainan Island. With an average water depth of 38 meters (the deepest water being less than 90 meters) and a flat seabed, the gulf encompasses an area of about 44,238 square kilometers (24,000 square nautical miles). It has been shared by both China and Vietnam but has never been demarcated by the two sides. From November 1885 to June 1887, representatives of the two sides conducted joint surveys of the Sino-Vietnamese land border and the islands in the Gulf of Tonkin. However, due to some constraints back then, many historical disputes remain to be addressed.