Abstract: As viewed with some theoretical and methodological topics of biogenic gas studies at home and abroad,the authors suggest that the formation of biogenic gases in the nature(by the reduiction of CO₂ or methane formed by the fermentation of acetic acid)should be dominated by combining factors,such as sedimentary environment,burial depth,climate and geological ages etc.,and the criteria of δ¹³C less than-55% and less than 0.5% could be reasoi1able indexes for the identification of biogenic gases.As for the analysis,subdivision and evaluation on the types of organic matter of biogenic gas source rocks,the authors of this paper donot believe that the traditional concept and method used in petroleum genlogical studies can continue to be fully used.