The Gulf of Thailand is located in the South China Sea (Pacific Ocean), surrounded by the countries Malaysia, Thailand, Cambodia and Vietnam. The north tip of the Gulf is the Bight of Bangkok at the mouth of the Chao Phraya River, near Bangkok. The gulf covers roughly 320,000 km².
The Gulf of Thailand is relatively shallow, the mean depth is 45 m, and the maximum depth only 80 m. This makes water exchange slow, and the strong water inflow from the rivers like the Chao Phraya or Mekong make the Gulf lower in salinity and also rich in sediments. At the height of the last ice age the Gulf of Thailand did not exist at all due to the lower sea level, but did instead continue the Chao Phraya river valley.