Great advancement has been achieved with polymer flooding after water flooding to enhance oil recovery in Daqing oil field in China. By using polymer flooding, the oil recovery can be improved 12%, and the total oil production is 10 million tons per year in Daqing oil field. However, there is still about 50% remaining oil kept in oil-bearing formation after polymer flooding. This paper gives the method of Quarternary Oil Recovery by using MEOR succeeding a polymer flooding. In this paper, several kinds of bacteria that can grow with polymer and crude oil as the carbon source have been screened. These bacteria are different from that of growing with carbohydrate as the only carbon source used in MEOR before. Evaluation was made on the physiological and biochemical characteristics of the screened bacteria, the ability of their degrading oil and polymer, the ability of their producing bio-surfactant, and on the core displacement test. The results show that the light component and the rheological property of crude oil have been increased due to the action of the selected bacteria, the paraffin content, the gel content and the freezing point of crude oil have been decreased. Also, due to the action of the bacteria, the acid value of oil has been raised by 64.5 times and the initial boiling point has been reduced 80°C. Moreover, the Newtonian Index, Delta viscosity and EOR Index have been increased. Core displacement shows that oil recovery can be improved 5% or 13% by using MEOR or with the following ASP system respectively. All of the experiments can be repeated perfectly.

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