� “JM” Block area is located in the Jambi Sub-Basin, South Sumatera Basin. The aims of this research are to analyze the overpressure zone in “JM” Block. The method used in this research to find the overpressure zone is by using a calculation Eaton Method with using log data, density log and sonic log. The results of analysis of density log and sonic log is illustrated in a graph of hydrostatic pressure, overburden, and the value of pore pressure. On this graph, overpressure zone, pore pressure value would exceed the value of the hydrotastic pressure and is below the overburden. On “JM” Block is known to have 5 (five) faults, with 4 (four) faults is normal fault which the trend southwest – northeast and 1 (one) dault is normal fault which the trend northwest – southeast. Zone overpressure in “JM” Block illustrated in isopach map and SSR (Sand Shale Ratio) map of Pendopo Formation. An area has >45 feet of shale thickness and with SSR (Sand Shale Ratio) smaller value could potentially have a greater overpressure. Overpressure mechanism in wells JM-1 and JM-2 is caused by the overburden in loading mechanism. It is supported also by changes in clay minerals that have not fully changed from smectite to illite. Overpressure mechanism in wells JM-3, JM-4, and JM-2 is caused by the generation of hidrocarbon in unloading mechanism. It is shown on geochemical data, that is Ro (vitrinite reflectance) of rocks is immature until peak mature, TOC (Total Organic Content) is 0,75 - >1,5% and the average quality is good.