Using aeromagnetic data in combination with other geophysical information, the authors studied basic characteristics of the Tan-Lu fault belt in the Bohai Sea area, discussed detailed features of the tectonic line passing through the sea area, and investigated the control role of the fault belt over the Bohai Sea Basin as well as the relationship between this fault belt and the oil and gas fields. The Bohai Gulf area seems to the authors to be a favorable place in search for volcanic type oil and gas accumulation. It is also pointed out that new oil and gas fields might be found along the major fractural line of the Tan-Lu fault belt and its lateral areas.