Gulf of Siam

Gulf of Siam

[sahy-am, sahy-am]
Siam, Gulf of: see Thailand, Gulf of.

The Gulf of Thailand (or Gulf of Siam) is a gulf that borders, but is not part of the South China Sea (Pacific Ocean). The gulf is bordered by Cambodia, Thailand and Vietnam. The northern tip of the gulf is the Bay of Bangkok at the mouth of the Chao Phraya River, near Bangkok. The gulf covers roughly 320,000 km². The boundary of the gulf is defined by the line from Cape Bai Bung in southern Vietnam (just south of the mouth of the Mekong river) to the city Kota Baru on the Malayian coast. At the height of the last ice age the Gulf of Thailand did not exist, due to the lower sea level, the location being part of the Chao Phraya river valley.


The gulf 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 make the Gulf low in salinity (3.05-3.25%) and rich in sediments. Only at the greater depths does water with a higher salinity (3.4%) flow into the gulf from the South China sea and fills the central depression below a depth of 50 m. The main rivers which empty into the gulf are the Chao Phraya (including its distributary Tha Chin River), Mae Klong and Bang Pa Kong Rivers at the Bay of Bangkok, and to a lesser degree the Tapi River into Bandon Bay in the southwest of the gulf.

Due to the tropical warmth of the water, the Gulf of Thailand harbours many coral reefs, and thus several diving resorts. Most popular for tourism is the island Ko Samui in the Surat Thani province, Pattaya Chonburi province, while Ko Tao is the center of the diving tourism.

Natural resources

The gulf also contains some oil and larger natural gas resources in Thai and Cambodian territorial water.


There is a territorial dispute in the area between Malaysia, Thailand and Vietnam. Malaysia and Thailand in particular have chosen to jointly develop the disputed areas.

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