With the development of national economy and increase in demend for petroleum resources

the evaluaion of marginal reserves has become more and more important. Based on the study of the characteristics of marginal reservesand problems encountered in evaluation by conventional criteria

new evaluation criteria are discussed. A new evaluationidea including the basis

the unit

the paramter and methods of evaluation are proposed. According to commercial oilflow standard

a new concept of productivity ratio(DBD) is also proposed. This thus solves the problems of comparabitity of produtivity between wells and of single well that puzzled people for a long time in the marginal reserves evaluation

and could realize the transformation from qualitative to quanitative evaluations.