Cyclic Steam Stimulation (CSS) is an enhanced oil recovery technique used to extract heavy crude oil from underground reservoirs. This method involves injecting steam into the oil reservoir, which heats the oil and reduces its viscosity, making it easier to flow. After a period of steam injection, the well is allowed to produce oil, and the cycle is repeated multiple times. CSS is particularly effective in areas where traditional drilling methods are less efficient due to the thick nature of the oil. It is commonly used in regions with heavy oil deposits, such as the Athabasca Oil Sands in Canada.