A method for determining the thermal maturity of a rock formation in a geological region of interest for hydrocarbon production, comprising: drilling a plurality of exploration wells to access the rock formation; obtaining mud gas isotope logging data for each of the plurality of exploration wells, the mud gas isotope logging data comprising isotopic values associated with an isotope in a mud gas; obtaining a vitrinite reflectance equivalent for each of the plurality of exploration wells, the vitrinite reflectance equivalent determined from a core sample (500, 504, 508, 512, 516) from each of the plurality of exploration wells; and determining a relationship between vitrinite reflectance equivalent and the isotopic values, the vitrinite reflectance equivalent indicating a thermal maturity of the rock formation, wherein obtaining the vitrinite reflectance equivalent for each of the plurality of exploration wells comprises: determining, for each of the plurality of exploration wells, a temperature at which the maximum rate of hydrocarbon generation occurs in a kerogen sample from the respective exploration well during a pyrolysis analysis; and/or an amount of bitumen in a core sample (500, 504, 508, 512, 516) obtained from the respective exploration well; and calculating the vitrinite reflectance equivalent from the temperature and/or the bitumen amount for each of the plurality of exploration wells. drilling a plurality of exploration wells to access the rock formation; obtaining mud gas isotope logging data for each of the plurality of exploration wells, the mud gas isotope logging data comprising isotopic values associated with an isotope in a mud gas; obtaining a vitrinite reflectance equivalent for each of the plurality of exploration wells, the vitrinite reflectance equivalent determined from a core sample (500, 504, 508, 512, 516) from each of the plurality of exploration wells; and determining a relationship between vitrinite reflectance equivalent and the isotopic values, the vitrinite reflectance equivalent indicating a thermal maturity of the rock formation, wherein obtaining the vitrinite reflectance equivalent for each of the plurality of exploration wells comprises: determining, for each of the plurality of exploration wells, a temperature at which the maximum rate of hydrocarbon generation occurs in a kerogen sample from the respective exploration well during a pyrolysis analysis; and/or an amount of bitumen in a core sample (500, 504, 508, 512, 516) obtained from the respective exploration well; and calculating the vitrinite reflectance equivalent from the temperature and/or the bitumen amount for each of the plurality of exploration wells. determining, for each of the plurality of exploration wells, a temperature at which the maximum rate of hydrocarbon generation occurs in a kerogen sample from the respective exploration well during a pyrolysis analysis; and/or an amount of bitumen in a core sample (500, 504, 508, 512, 516) obtained from the respective exploration well; and a temperature at which the maximum rate of hydrocarbon generation occurs in a kerogen sample from the respective exploration well during a pyrolysis analysis; and/or an amount of bitumen in a core sample (500, 504, 508, 512, 516) obtained from the respective exploration well; and calculating the vitrinite reflectance equivalent from the temperature and/or the bitumen amount for each of the plurality of exploration wells.