island in the Gulf of Thailand, belonging to Vietnam. Lying 7 miles (11 km) off the Cambodian coast south of Bok Koŭ (formerly Bokor) and 43 miles (69 km) west of the west coast of southern Vietnam, the partially forested island is almost 30 miles (48 km) long from north to south and has a maximum width of 17 miles (27 km). It has an area of 230 square miles (596 square km). The climate is tropical monsoonal year-round with a short two- to three-month drier winter season. The eastern half has elevations ranging from about 2,000 feet (600 m) in the north to about 1,200 feet in the south. The western half and the southern tip are considerably lower.

The island's economic activities include the mining of jet (a dense, black mineral, a variety of coal) and anthracite, lumbering, and the production of pepper, cocoa, coffee, betel, and coconuts. Following World War I the French imported 3,000 colonists from Tonkin (northern Vietnam) in an unsuccessful scheme to establish plantations. Fishing is important, and nuoc mam (a fish-sauce condiment), copra, and tortoise shells are exported. A garrison and a harbour have been built on the island. Duong Dong, in the west, is the chief town, and at An Thoi, on the southern tip, there is an airport. South of the island lie the associated Anthoi Islands, which have iron-ore deposits.