Abstract <p>Free and sorbed gases in the Middle Amur sedimentary basin are found to contain up to 73.42% and 1.59% of methane and its homologues (in total), respectively. Based on the δ¹³C-CH₄-C₂H₆ isotopic composition and established gas-geochemical indicators, such as weight concentrations, molecular weight of the hydrocarbon fraction, and the coefficient of fatness of hydrocarbon gases, nine source gases of biochemical and thermogenic origin are identified. Based on the available and obtained data, a brief assessment of the basin’s oil and gas potential is performed.</p>