The present invention relates to the oxidation, by means of oxygen or a gas containing it, of hydrocarbons to the corresponding carboxylic acids, alcohols and/or ketones or of alcohols and/or ketones to the corresponding carboxylic acids. It consists more precisely in a process for oxidizing hydrocarbon, alcohol and/or ketone, using oxygen or a gas containing it, in liquid phase and in the presence of a catalyst dissolved in the reaction medium, characterized in that the catalyst comprises a soluble manganese compound and at least one soluble chromium compound.