The article shows the problem of environmental pollution when using fuel oil in thermal and power plants. The use of high sulfur fuel oil to ensure the operation of cogeneration plants, thermal power and boiler plants in stationary equipment in Ukraine has been prohibited since 2018. The potential ban of using of this type of fuel for the operation of mobile emission sources, including maritime transport has become an international trend. Therefore, the aim of the work was to substantiate the requirements of national legislation and to determine the advantages of low-sulfur fuel oil in comparison with high-sulfur. The article provides an estimate of emissions of harmful substances, including suspended solids, sulfur, nitrogen, carbon, vanadium compounds, organo-containing volatile compounds during the combustion of fuel oils with different chemistry. The tasks of the work were to evaluate the chemistry of the studied fuels, the efficiency of the treatment equipment, the processes of binding pollutants with ash, and the calculation of the emission factors of pollutants and the values of their emissions during the combustion of a ton of fuel in the furnaces of power and heating equipment. The paper used calculation methods for determining emissions into the air during fuel combustion based on indicators of emissions of pollutants contained in the emissions, according to the methodology of the Ukrainian Scientific Center of Technical Ecology, developed using international guidelines and standards. The above calculation of emissions of harmful substances during the burning of fuel oil can used in the development of permits by enterprises polluting the atmospheric air. When conducting a comparative analysis, high values were determined for sulfur dioxide emissions for high sulfur fuel oil, for other indicators, pollutant emissions during the combustion of various types of fuel oil are similar. The article also determined that most of the carbon in the studied fuels goes into carbon dioxide emissions and a smaller part – into carbon monoxide emissions. Most of the nitrogen goes into the emission of nitric oxide and a smaller part – into the emission of dinitric oxide. Thus, the work proved the danger of high-sulfur fuel oil in terms of sulfur compounds emissions, however, when using sulfur reduction technologies, such fuel oil can also be used as low-sulfur fuel, since they have a similar qualitative and quantitative composition of emissions of other pollutants.