The alteration of iron-bearing minerals induced by hydrocarbon microseepage above oil/gas reservoirs has been evaluated using measurements of soil magnetic susceptibility κ, geochemical compositions (gas hydrocarbon and alteration carbonateΔC), and composition and concentration of iron-bearing minerals. The analyses were performed along two profiles across the Qiangtang basin in Tibet, China: the Nuoermahu-Xuehuanhu profile (C) and the Mugari-Huochetoushan profile (E). Results show that three strong magnetic anomalies (C1, E1 and E2 anomalies) are related to the distribution of Neogene volcanic rocks on the surface in the Gangmacuo-Xiyaergang uplift. Two other anomalies (C2 and E4 anomalies), characterized by both moderately amplitude magnetic susceptibility and elevated soil gas hydrocarbons, occur near fault zones in the Cuoni-Donghu synclinorium. These latter anomalies display characteristics of hydrocarbon microseepage anomalies commonly associated with oil and gas accumulations. Their presence in the Cuoni-Donghu synclinorium suggests that parts of the Qiangtang basin may have significant petroleum potential.