Abstract: A mixture of petroleum acids can effectively be separated from a petroleum distillate containing such a mixture by adjusting the molecular weight distribution of the petroleum acids in the mixture so that at least 10% of the acids have a molecular weight of less than 260 and at least 50% of the acids have a molecular weight of more than 260, treating the petroleum distillate with an aqueous solution of sodium hydroxide which solution is added with at least 5% of a sodium salt, calculated on the weight of the aqueous solution, at a temperature of at least 85.degree. C in one or more reactors to the formation of a reaction mixture containing three phases and causing said three phases to separate.