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Using a theoretical model and mass isotopic balance, biogas (methane and CO2) released from buried products at their microbial degradation was analysed in the landfill of municipal and non-toxic industrial solid organic waste near Kaluga city, Russia. The landfill contains about 1.34×106 tons of waste buried using a 'sandwich technique' (successive application of sand-clay and waste layers). The δ13C values of biogenic methane with respect to CO2 were-56.8 (±2.5) ‰, whereas the δ13C of CO2 peaked at+9.12‰ (+1.4±2.3‰ on average), reflecting a virtual fractionation of carbon isotopes in the course of bacterial CO2 reduction at the landfill body. After passing through the aerated soil layers, methane was partially oxidised and characterised by δ13C in the range of-50.6 to-38.2‰, evidencing enrichment in 13C, while the released carbon dioxide had δ13C of-23.3 to-4.04‰, respectively. On the mass isotopic balance for the δ13C values, the methane production in the landfill anaerobic zone and the methane emitted through the aerated landfill surface to the atmosphere, the portion of methane oxidised by methanotrophic bacteria was calculated to be from 10 to 40% (averaged about 25%). According to the theoretical estimation and field measurements, the annual rate of methane production in the landfill reached about 2.9(±1.4)×109 g C CH4 yr-1 or 5.3(±2.6)×106 m3 CH4 yr-1. The average rates of methane production in the landfill and methane emission from landfill to the atmosphere are estimated as about 53 (±26) g C CH4 m-2 d-1 (or 4 (±2) mol CH4 m-2 d-1) and 33 (±12) g C CH4 m-2 d-1 (or 2.7 (±1) mol CH4 m-2 d-1), respectively. The calculated part of methane consumed by methanotrophic bacteria in the aerated part of the landfill was 13(±7) g C CH4 m-2 d-1 (or 1.1(±0.6) mol CH4 m-2 d-1) on average. [ABSTRACT FROM AUTHOR]