The lower Tertiary Eh3 is divided into two sections:the upper members of Eh3 and the lower members of Eh3 in the Biyang Depression.The first section is generally regarded as a key target of oil and gas exploration,but the resource potential of the lower members of Eh3 has been neglected.We have obtained new knowledge about Eh3 from comprehensive geological research.The lower members of Eh3 are high-quality and main source rocks,which have good oil and gas resource potential.This is a new direction for oil and gas exploration.The geochemistry characteristics of source rocks of the lower members of Eh3 in the lower Tertiary of the Biyang Depression were analyzed in detail.A basin modeling method was applied to hydrocarbon generation of the lower and upper members of Eh3 source rocks,the oil and gas resource potential was comparatively analyzed,and then favorable tectonic zones were pointed out.In the lower members of Eh3,a set of semi-deep lake to deep lake high-quality source rocks occurs rich in algae organisms,mainly of type Ⅱ1,with a high abundance of organic matter.Most of the source rocks are just in the peak stage of hydrocarbon generation,which is a favorable foundation for forming abundant oil and gas resources in the Biyang Depression.The comparative analysis of the hydrocarbongeneration quantities between lower and upper members of the Eh3 source rocks shows that the lower members of Eh3 have good oil and gas resource potential,and the hydrocarbon-generation quantity accounts for 51％ of the total in Eh3.Specifically,the oil-generating quantity accounts for 50％ of the total and the gas-generating quantity accounts for two thirds of the total.Therefore,source rocks in the lower members of Eh3 of the Biyang Depression have good oil and gas resource potential,which is a key factor for future deep oil and gas exploration.