Abstract: All surface geochemical exploration methods for oil and gas are based on the theory that hydrocarbons generated and trapped at depth seep in varying but detectable quantities to the surface, and the main components detected are usually C₁-C₅ hydrocarbons. The C₁-C₄ hydrocarbons could come from degradation of organic matter by microbial organisms, while the gasoline range hydrocarbons are totally sourced from thermogenic processes. Therefore, the detection of gasoline range hydrocarbons in soils or sediments could be the most direct evidence for hydrocarbon seepage and the method used to detect the C₆-C₁₂ range hydrocarbons could be a useful technique for surface geochemical exploration method for petroleum. However, because the concentration of gasoline range hydrocarbons in the soils or sediments are usually very low, and the present techniques for detecting those hydrocarbons are not adequate, the gasoline range hydrocarbons have seldom been used in surface geochemical exploration for oil and gas. In this study, the headspace single-drop microextraction (HS-SDME) technique coupled with gas chromatography-flame ionization detection (GC-FID) was employed to determine C₆-C₁₂ gasoline range hydrocarbons in well drilling mud sample. The results show that the C₆-C₁₂ hydrocarbons in the samples could be detected by HS-SDME, and the reservoir depth determined by the concentration of C₆-C₁₂ hydrocarbons was the same with the actual petroleum reservoir depth, which indicated further that the HS-SDME method could be used in geochemical exploration for petroleum.