1. Extraction of oxygen compounds will decolorize middle-distillate fuels, improve the thermal stability and cleanliness level, and reduce the charging tendency, and will also lead to a considerable reduction of the tendency to form emulsions with water. 2. After removing the oxygen compounds, the antiwear properties of the fuels are poorer, and they are more susceptible to oxidation. 3. Before the accumulation of oxidative-condensation products (this accumulation requiring a prolonged period), the oxidation of the purified fuels proceeds with the formation of oxygen compounds that are for the most part readily soluble in the fuel.