Abstract: The concept of the accumulation amount is briefly introduced. Attention is paid to discussing three different views on accumulation coefficient. It is considered that the coefficient should be equivalent to the percentage of the accumulation amount of oil and gas relative to the volume of primary migration in source beds. Furthermore, the relation between the coefficient of accumulation and that of hydrocarbon expulsion is discussed. Macroscopically the former is much larger than the latter. The mean value for the accumulation coefficient of oil and gas is about 50%; and that of hydrocarbon expulsion, generally ranges from 10-20%. Finally, the collocation system of a source-reservoir pair should be regarded as an unit in analogue computation. Such consideration should be applied in the research of resources estimation.