Measurements of magnetic, geochemical and mineralogical parameters of soil and rock above oil and gas reservoirs from the Ordos Basin, Jianhan Basin, Subei Basin, Tarim Basin and Songliao Basin et al., China indicate that hydrocarbon alteration due to geochemical processes had been generated commonly and lead to magnetic increasing of soils and rocks (it is called magnetic response). Magnetic responses related to hydrocarbon alteration are controlled mainly compositions and contents of iron-bearing minerals, lithologies in soils and rocks and structure on subsurface in situ. For example, locations of magnetic anomalies correspond to faults in cover rock (e.g. Huayuan oil field, Jianghan basin and Chujialou oil field, Subei basin). Magnetic intensity of soil in near surface, loess is the most strongest (susceptibility κ is up to 1800 x 10^-6SI), sand or subsand is medium- intensity (κ<1000x10^-6SI) and clay is the most weakness  (κ<100x10^-6SI).

According as compositions of iron-bearing minerals related to geochemical processes, hydrocarbon alterations could be divided mainly into three categories. They are iron oxides (e.g. magnetite, maghemite, and hematite), the iron sulphides (pyrite and pyrrhotite) and iron carbonate (siderite), respectively. As the factors controlling hydrocarbon microseepage above oil and gas reservoirs are very complex, so, the reliable relations between magnetic response and hydrocarbon alteration need to study in further.