Based on the data available, this paper describes the distribution of solule gaseous hydrocarbon within underground water in various geologic bodies and its application in search for hydrocarbon deposits. In using this method, particular attention should be paid to the association of gases of hydrocarbon type, the proportion of heavy hydrocarbon and the humidity in combination with other hydrogeochemical indexes. The measurement of carbon isotopes may throw light on the geneses and attributes of various gases. In reconnaissance and exploration stage, the study should mainly focus on the soluble gaseous hydrocarbon in upper hydrogeochemical zone, which might provide data for preliminary oil prediction and indicate favourable areas for fur further work; whereas in exploitation stage, an investigation into the soluble gaseous hydrocarbon in the lower hydrogeochemical zone may indicate relatively reliable exploration sectors and drilling sites.