Abstract: Based on the essential character, the terms used usually in oil economics are clarified due to people's misunderstanding, and the main factor that there are several participants who have different benefits contributed to the complexity of oil economics is pointed out. Moreover, the complexity is described in details by reviewing the history of the evolvement about oil market structure. In spit of the complexity, by investigating the constraints of oil market, the interpretation of the rising oil price and non-crisis is obtained. At last, the available approach to study oil economics deeply is pointed out.