The present invention relates to an aqueous oxidizing composition for treating keratin fibers, comprising: —at least one oxidizing agent; —at least 40% by weight of at least one oil; —at least one phosphoric acid mineral salt; —the pH of the oxidizing composition being less than or equal to 5. The composition in accordance with the invention may be used for dyeing, bleaching or permanently reshaping keratin fibers. It produces ready-to-use compositions that give good dyeing, bleaching or permanent reshaping properties without degrading the keratin fibers and without impairing their cosmetic properties. Furthermore, the composition in accordance with the invention shows good stability over time, especially to storage at high temperatures, for example of about 45° C.