The paper presents empirical formulae for calculation of the amount of methane obtained from landfills using Peavy's or Buswell's equations. Using the Peavy equation it should be noted that the decomposition rate in unmanaged landfills, as measured by gas production, reaches a peak value within the first two years and then slowly levels off, continuing, in many cases, for periods up to twenty-five years or more. The total volume of gases released during anaerobic decomposition can be estimated in a number of ways. If all organic constituents of waste (except for plastics, rubber and leather) are represented by a general formula C_aH_bO_cN_d, the total volume of gas can be estimated by using equations from the article, assuming complete conversion to carbon dioxide and methane. In the Slovak Republic 1.66 mil ton of municipal organic waste was produced in 2001, which, according to the calculations, can form ca. 6.8 × 10⁸ m³ of methane.