The Gulf of Thailand, historically known as the Gulf of Siam, is a shallow inlet adjacent to the southwestern South China Sea, bounded between the southwestern shores of Mainland Southeast Asia and the northern half of the Malay Peninsula. It is around 800 km (500 mi) in length and up to 560 km (350 mi) in width, and has a surface area of 320,000 km2 (120,000 sq mi). The gulf is surrounded on the north, west and southwest by the coastline of Thailand; on the northeast by Cambodia; and the Mekong Delta region of Vietnam. It opens to the South China Sea in the southeast.