A washing composition based on biodegradable surfactants and an alkaline buffer system has been developed for oil sludge reclamation. A specially selected ratio of the components is optimal owing to the synergistic effect of their interplay. Washed oil sludge and soils do not require further purification and can be processed into building materials or used as a filling material for cluster sites or roads. The contaminated aqueous solution remaining after oil sludge washing is subjected to microbiological treatment with a commercial biopreparation. The biodegradation of saturated hydrocarbons in the spent solution is more than 90%. After biodegradation, the water is recycled to wash a new portion of oil sludge or is used for sanitary or other industrial needs.