This paper elucidates the principle of applying magnetism of Quaternary sediments to the oil and gas investigation: underground oil and gas accumulations would produce magnetic minerals and form various magnetic parameter anomalies in near-surface Quaternary sediments. Types of magnetic minerals forming magnetic anomalies were identified, and it has been found out that there exist magnetotaxis bacteria in soils of oil fields. The application of this method to the investigation of oil and gas distribution in areas of nearly 450 km² within five oil field shows that various magnetic anomalies (κ、M n、M r、I r and I κ) assume forms of composite anomalies, with their formation and distribution characteristics controlled by oil and gas activities, channelways and environmental conditions. Data available demonstrate that magnetic composite anomalies can reflect distribution of oil and gas activities in oil fields and that, as one of the integrated prospecting methods, the method should be further spread.