The density, kinematic viscosity, sulfur content, water content, and heat of combustion of greater than 50 samples of residual fuel oils, water-residual-fuel-oil emulsions, and spent oils are determined experimentally. The viscosity and higher heat of combustion of water-residual-fuel-oil emulsions are shown to depend on the water content. The optimal water content in water-residual-fuel-oil emulsions is determined using numerical viscosity values. The ranges over which the density and higher heat of combustion of the test samples vary are determined and analyzed. Variants for calculating the heat of combustion of oil products are studied. Equations for calculating the higher and lower heats of combustion of heavy boiler oils, including water-residual-fuel-oil emulsions, are proposed.