The aim of the present investigation was to determine time variation of biogas composition at the gas collection network on the ‘Barycz' landfill site in Cracow, Poland, as well as the influence of operational and meteorological conditions on the biogas composition. The study of biogas composition at selected gas wells and gas collectors was conducted using a portable IR landfill gas analyser. The methane concentration in biogas on the part of the landfill site currently in operation varied in the range 59-63% vol. and on the reclaimed part of the landfill, in the range 42-62% vol. It was found that biogas composition is significantly affected by operational conditions and meteorological parameters. For example, methane concentrations were more constant when the pressure in the installation was above the ambient atmosphere than when it was below, where fluctuations of 15% vol. were seen. Low air temperature, high precipitation and high atmospheric pressure, which lower the permeability of the outer layer of the landfill, result in higher quality of the biogas getting to the gas collection system.