The possibility of reducing sulfur content of Astrakhan gas condensate in residual fuel oil by oxidative desulfurization using ozonized air is examined. The optimal conditions for oxidizing with ozone and for thermal decomposition of oxidized sulfur compounds are determined. The sulfur content in residual fuel oil can be reduced from 2.86 to 0.48 wt. %, whereupon hydrogen sulfide is removed completely from the residual fuel oil and the combustion heat increases.