Even though distinction of Asmari and Bangestan reservoirs by usually impermeable strata of Pabdeh and Gurpi Formations, connectivity of these reservoirs is not unlikely owing to the complex active tectonics of SW Iran. Therefore, an integration of reservoir geochemistry and engineering approaches were used to investigate connectivity of the reservoirs mentioned above in Gachsaran Oilfield. Biological markers specified a unique carbonate-marl source rock deposited in a marine environment under anoxic-suboxic conditions for hydrocarbons entrapped in both reservoirs. Strong marine organic matter signatures along with robust pieces of evidence of the partial contribution from land plants were detected.Moreover, all oils exhibit an identical level of thermal maturity as high as the maximum hydrocarbon generation stage. Along with genetic relationship, connectivity of Asmari and Bangestan reservoirs was also proved using star diagrams, the concentration of heavy elements, PVT test results, and effect of the gas injection into Asmari cap on pressure trends of both reservoirs. These results will improve the efficiency of reservoirs management and maintenance projects. The possibility of producing from both reservoirs from each well is also deduced, which significantly decreases drilling cost. Finally, applicability and reliability of reservoir geochemistry approaches were approved, especially at the early production stages of fields where the pressure data are not available.