The effects of additives based on carbon nanotubes, which are a versatile nanomaterial for producing substances having fundamentally new or significantly altered physicomechanical and physicochemical properties, are studied in order to improve the quality of heavy fuel oil having a large proportion of residuals. Results from studies of the rheological properties of furnace fuel oil and water-oil emulsions mixed with suspensions of domestic carbon nanotubes in surfactant dispersions are presented. The mechanisms of action of carbon nanotubes on the dynamic viscosity of the fuel oil are studied. It is shown that energy-saving and resource management problems can be solved by incorporating carbon nanotubes into the boiler fuel in order to reduce the cost of meeting the needs of plants and boiler houses.