NOVELTY - Microbial conversion of petroleum is stimulated (102) in zone to biogenerated methane. Gas containing biogenerated methane is produced (104) from zone to surface. Production parameters including reservoir pressure and an isotopic composition of at least one of methane, carbon dioxide or hydrogen included in produced gas, are monitored (106) during production of gas. At least one of stimulation of microbial conversion to control composition of produced gas or gas saturation in zone to control mobility of biogenerated methane is adjusted (108) based on monitored parameters.    USE - Manufacture of biogenerated gas e.g. hydrogen, carbon dioxide and methane (claimed) from zone in reservoir.    ADVANTAGE - The biogenerated gas is efficiently manufactured from zone in reservoir with reduced energy and without effecting environment.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for system for producing biogenerated gas from zone in reservoir. The system comprises an isotope fractionation model simulator configured to predict a composition of produced gas from the zone when production of biogenerated gas is occurred under optimal conditions, a production parameter monitoring engine configured to receive production parameter data of production process including reservoir pressure and an isotopic composition of at least one of methane, carbon dioxide or hydrogen included in produced gas, and an analysis engine configured to receive the predicted compositions of produced gas from the isotope fractional model simulator and the production parameter data from the production parameter monitoring engine, compare the predicted composition of produced gas to the actual isotopic composition of the produced gas and provide an analysis of the efficacy of the production process based on the comparison.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of flowchart illustrating manufacture of biogenerated gas.    Stimulation of microbial conversion of petroleum (102)    Production of gas containing biogenerated methane (104)    Monitoring of production parameter (106)    Adjustment of stimulation or gas saturation (108)