The Junggar Basin is one of the largest and most petroliferous superimposed petroleum basins in China. The central depression area has become the frontier field for petroleum exploration. The characteristics of potential source rocks and reservoir sandstones, and the pressure regime in the central Junggar Basin were studied. Permian shales are dominated by hydrogen-rich, oil-prone algal organic matter, and Jurassic mudstones are dominated by hydrogen-poor, higher-plant derived organic matter. These source rocks are widespread and have been mature for hydrocarbon generation, suggesting good to excellent exploration potential, both for crude oils and for natural gases. The deeply buried Jurassic sandstones usually have low porosity and permeability. However, sandstones beneath the Jurassic/Cretaceous unconformity display relatively high porosity and permeability, suggesting that meteoric water leaching had improved the quality of the sandstones. Overpressure developed over much of the central Junggar Basin. The overpressured rocks are characterized by slightly increased interval transit time, low sandstone permeability, increased organic matter maturity, and high relative hydrocarbon-gas contents. Mudstones in the overpressured system have quite the same clay mineral compositions as mudstones in the lower part of the normally pressured system. Overpressure generation in the central Junggar Basin is best to be explained as the result of hydrocarbon generation and fluid retention in low-permeability rocks. Petroleum generated from Permian and Jurassic source rocks could migrate laterally through preferential petroleum migration pathways and accumulated in structural traps or lithological traps in the overpressured system, or migrate vertically through faults/ hydraulic fractures into the overlying, normally pressured system and accumulate in structural or lithological traps. Therefore, commercial petroleum reservoirs could be potentially found in both the overpressured system, and in the normally pressured system. pressure regime, overpressure generation, oil charge, petroleum exploration potential, Junggar BasinAs petroleum exploration and development in Cenozoic lacustrine basins increases, finding oil and gas reserves in superimposed basins has become an important strategy in China [1,2] . Superimposed basins refer to sedimentary basins that resulted either from the contemporaneous composition of different proto-type basins or from the superimposition of proto-type basins of different stages [3] . The Junggar Basin, which began to develop in Carboniferous, is one of the largest and most petroliferous superimposed sedimentary basins in China. So far over 20 major oil fields have been found in the basin. These fields had produced a total oil output of over 2×10 8 t by the end of 2005 [4] .Up to the present, most commercial oil and gas fields were found in basin margins or on the uplifts in the Junggar Basin. As petroleum exploration in basin margins and uplift areas goes into the mature phase, finding