The standards and regulations linked with the environmental protection and the vehicles are more and more restrictive. Standard EURO VI define the acceptable limits for exhaust emissions of new vehicles sold. Because of that, Selective Catalyst Reduction systems are used in a new vehicles with the heavy-duty type engines. This paper presents a study of the SCR system in public transport vehicles of the Municipal Transport Company (MPK) in Lublin, Poland. The tests were performed to study the power consumption of the SCR (the urea applicator into the catalyst) and calculate the results per unit of fuel. The amount of fuel for the Solaris Trollino 12 trolleybus was estimated and the energy demand found was of the order of 343 kWh/year. This gives a low diesel fuel consumption, because only 34,3 litres per year. The study also shows a graph of the daily demand of energy by the SCR system in public transport vehicles.