Abstract: The Cenozoic petroleum system in the Wan'an Basin is made of the Oligocene-Middle Miocene source rocks,the Pre-Tertiary bedrock-Miocene reserviors and the Pliocene-Quaternary caprocks.The traps are dominated by fault blocks,anticlines and reefs.The main source rocks reached the peak of hydrocarbon generation and expulsion in the end of the Middle Miocene and presently are in the high-to over-matured stage.Various traps were formed before the end of the Middle Miocene and hydrocarbon accumulation was in its way in the end of the Pliocene.Hydrocarbon migrated both horizontally and vertically in short distance and was caught up by a resistive system.The traps were over-or normal-charged.In a word,the Wan'an Basin is favorable for hydrocarbon exploration as a result of its long hydrocarbon generation,late accumulation and good preservation.