The flotation of low-quality Russian and Mongolian coal by means of spent motor oil is investigated. Ozonization is used to improve the flotational properties of the spent oil. The optimal ozonization depth of oil used to enrich coal of poor metamorphic development is 5–6 g/kg. Ozonization increases the oil’s content of oxygen-bearing heteropolar compounds, which determine its flotation properties. In addition, the viscosity declines. The use of ozonized spent oil improves the flotation of gas coal by 24%. Flotation of naturally oxidized gas coal by spent oil, before and after ozonization, is poor and requires large quantities of reagents.