Oyster sauce is made from the oyster extracts. The cooked oyster extract is thickened with sugar, cornstarch and salt and finally made into a thick dark condiment. There is also vegan oyster sauce variety available which is made using mushrooms, but still is treated as oyster sauce. The Chinese brand Lee Kum Kee is credited with the invention of oyster sauce. It is popularly used in Chinese, Thai, and Vietnamese cuisines.