After Poland’s accession to the European Union, CN G supply began to be popularized. Jelcz buses powered by engines using diesel and CNG were used for comparative studies. The analysis was performed based on actual data obtained from the observation of the use of buses in the Municipal Transport Company in Przemyśl (MZK Przemyśl). We present, among other things, a comparative analysis of the direct operating costs of public transport buses powered by compressed natural gas and diesel fuel. CNG as a fuel allows to reduce the emission of harmful substances to the atmosphere, which is not without significance in the case of public transport, and this aspect of CNG gas use should be emphasized the most. The research showed differences in the operation and service of the vehicles powered by CNG installation in relation to the vehicles powered by diesel fuel, which may be important in connection w ith the conduct of transport activities.