The feasibility of biochemical oxidation of a mixture of waste petroleum oils has been shown using a model system with the introduction of hydrocarbon-oxidizing microorganisms represented by the Pseudomonas stutzeri, Pseudomonas putida, Bacillus cereus, and Arthrobacter globiformis species. The number of the microorganisms increases to 45 x 10(9) CFU/mL of medium during the oxidation. The proposed method involving the discharge of metabolic products during the experiment ensures the biodegradation efficiency on the order of 92% for 60 days starting from a waste oil concentration of 25 or 50 wt %. It is shown that all of the hydrocarbons present in the waste oil have been microbiologically oxidized by 79-100%. A mixture of waste vacuum oils has been subjected to instrumental analysis. The study has revealed that the biodegraded oil contains almost no oxygenated compounds in the free form. All the intermediate metabolites pass to the aqueous phase and either undergo complete mineralization or are included in the metabolism of the bacterial cell.