The Gulf of Thailand, also known as the Gulf of Siam, is an inlet of the South China Sea and borders Cambodia, Thailand and Vietnam. The western shores of the gulf border the Malay Peninsula, while the rest of the gulf borders mainland Southeast Asia.

The Gulf of Thailand contains three major Thai islands popular with tourists to the south—Ko Samui, Ko Pha Ngan, and Ko Tao—and three islands popular with tourists to the north—Ko Samet, Ko Chang, and Ko Kut. The gulf boasts some of the best beaches and diving in the world. Most of the tourist destinations in the gulf are Thai, although many of the relatively untouched islands off of the southern coast of Cambodia are beginning to receive visitors. The gulf is quite shallow, with an average depth of 45 meters, and the deepest point only 80 meters.

• South China Sea Project