NOVELTY - Method for producing biogas, involves measuring content of biogas, methane and optionally metals in fermentation tank, determining proportion of constituents and amount of fermentation catalyst comprising mixture of methanol, glycerol and optionally further additive constituents, and a time for adding the catalyst according to the above-cited measurements, adding the predetermined catalyst to the fermentation tank in the predetermined time, and adding fresh organic sludge into the fermentation tank.    USE - The method is useful for producing biogas in anaerobic methane fermentation of organic sludge chosen from industrial organic sludge, municipal organic sludge and agricultural organic sludge.    ADVANTAGE - The method increases yield of biogas and methane content in biogas, ferments any type of organic sludge, optimizes propagation of fermentation microorganism, stabilizes production of biogas and fermentation process, and improves efficiency of utilization of organic sludge components, hence it reduces content of organic components in fermented residues.    DETAILED DESCRIPTION - Method of producing biogas in anaerobic methane fermentation of organic sludge in a fermentation tank, involves (a) measuring contents of biogas, methane and optionally metals in the fermentation tank, (b) determining proportion of constituents and amount of a fermentation catalyst comprising a mixture of methanol, glycerol and optionally further additive constituents, and time for adding the catalyst based on the above-cited measurements, (c) adding the predetermined catalyst to the fermentation tank in the predetermined time, and (d) adding fresh organic sludge into the fermentation tank, where at least one first cycle of the steps (a)-(c) is carried out until a state of stabilization of biogas production is achieved and at least one second cycle of steps (a)-(c) is carried out using fermentation catalyst comprising vegetable fatty acids. An INDEPENDENT CLAIM is included for catalyst, which comprises (in wt.%): methanol (20-25), glycerol (5), fatty acids (5), and water before achieving the state of stabilization of biogas production, and methanol (10-15), glycerol (20-25), fatty acids (3-10) and water after achieving the state of stabilization of biogas production.