Oils produced from the Palogue Oilfield, Melut Basin, Sudan are medium oils (203???查原稿） formation water was formed due to the charge of fresh water into the Paleocene strata, and high TAN oils were formed due to biodegradation by NaHCO₃ formation water, and faulting-caused CO₂ intrusion from deep crust accelerated the forming of high acidity oils. The normal oils generated lately charged into the Paleogene reservoirs to form mixed oils with biodegraded oils, and finally, formed high acidity oils with various TANs.