Cyclic steam stimulation (CSS) is an enhanced oil recovery technique used to extract heavy crude oil from underground reservoirs. The process involves injecting steam into the well to heat the oil, reducing its viscosity and making it easier to flow. After a period of steam injection, the well is allowed to produce oil, which can be collected for processing. This method is particularly effective in areas where traditional drilling techniques are less efficient due to the thick nature of the oil. CSS is commonly used in regions with heavy oil deposits, such as the Athabasca Oil Sands in Canada.