Some specialists hold that the generation of hydrocarbons by immature source rocks is a prevalent geochemical phenomenon in many Cenozoic basins of China. This view contains a contradiction. In some fault depressions of the Subei basin, eastern China, there exist the equal subsurface temperature and the same maturity at different depths and the parallel-shallowing distribution of the maturity index and the burial depth of the samples. This phenomenon is due to the particular geological setting of the ancient burial depths being greater than the present ones (or called the degenerative thermal .history). If a curve of the hydrocarbon yield is drawn with the restored maximum palaeoburial depths, the phenomenon of earlier generation of hydrocarbons at low subsurface temperatures can disappear. Now that the phenomenon of hydrocarbon generation by immature source rocks does not exist, no immature oil will exist. The wrong view of hydrocarbons generation by immature source rocks mainly originate from the underestimation of the u-plift amplitude of such basins in the late stage and the unbalance of the uplift.