Ko Pha-ngan is an island in the Gulf of Thailand in Surat Thani Province of southern Thailand. Ko Pha-ngan has two sister islands: the larger Ko Samui to the south and the smaller Ko Tao to the north.Estimated perimeter: 40 km (25 mi) From mainland: about 55 km (34 mi) From Ko Samui: about 15 km (9.3 mi) From Ko Tao: about 35 km (22 mi) Main town: Thong Sala Highest Point: Khao Ra, 630 m (2,070 ft)

The Gulf of Thailand, also known as the Gulf of Siam, is a shallow inlet in the southwestern South China Sea, bounded between the southwestern shores of the Indochinese Peninsula 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 coastlines of Thailand, on the northeast by Cambodia and the Mekong Delta region of Vietnam, and opens to the South China Sea in the southeast.