Abstract: This paper is a general review of some of the problems related to the evaluation of an oil and gas basin at its early stage of exploration.In the opinion of the author,a study of the composition and morphology of the sedimentary deposit of a basin is essential to the preliminary estimation of its oil and gas reserve.He points out that the currently adopted volumetric method is not very accurate,as the correlation between the sedimentary deposit and hydrocarbon reserve expressed by corelation coefficient of the order of only +60% is not so close as expected.If deposits of different ages with different prospective reserves are taken into account,the corelation coefficient may be increased to +73～+95%.Besides,the size and structural position of the basin,as well as the type of oil and gas field,are all correlated with hydrocarbon reserve.Secondly,fixed carbon ratio,seepages along the margin of the basin,dispersed asphalts in outcrops and oil and gas shows in exploratory wells are useful indicators of the preservation of hydrocarbons.The author has cautioned against the possible overworking of the prevailing "thermal windows" concept.Thirdly,the data.from 18 oil and gas basins show that the corelation coefficient for the dispersed asphalts in sediments and hydrocarbon reserve is as high as +95%.It is presumed that the content of dispersed asphalts in sediments may be taken as the basis for direct estimation of prospective hydrocarbon reserve.Fourthly,study of the changes of sedimentary facies resulted from the advance and retreat of seas is one off the important steps in the evaluation of oil and gas basins; reflection seismic data may provide more accurate clues for the location of the facies changes.Fifthly,analogy of sedimentary basins is another way of evaluating hydrocarbon reserves.Geographic proximity,geologic conditions,factors contributing to the formation of oil and gas pools etc.are among the more important items that should be taken into consideration.Lastly,mention is made of the various methods of direct detection of hydroearbons attempted in China so far without noticeable success,except the surface radioative prospecting conducted in Daqing that claims an estimated credibility of 50～70%.