Abstract: Process for the preparation of a tenside mixture, wherein a starting mixture containing an alkali metal salt of an alkyl sulfonic acid is treated with a concentrated sulfuric acid solution in an amount in excess of the amount needed for converting the salts to organic acids with stirring and cooling such that the temperature of the mixture does not exceed about 35.degree. C., the reaction mixture being allowed to separate into two layers, one layer containing the organic acids, wherein the one layer containing the organic acids is separated and neutralized with di- or triethanolamine in order to prepare di- or triethanolamine salts of the said acids.