Abstract: An improved process is provided for the continuous sulphonation and/or sulphation of organic substances with sulphur trioxide gas mixed with an inert gaseous diluent, at an increased production rate without impairment of product quality, while minimizing discoloration of the product, and the amounts of unsulphonated product in the product, and of unreacted sulphur trioxide in the residual gaseous mixture, by limiting the amount of sulphur trioxide introduced ab initio into the organic liquid to be sulphonated and/or sulphated to not exceeding 7%, and preferably within the range from about 0.25 to about 5%, of the stoichiometric amount required for the desired sulphonated or sulphated product, introducing the remaining sulphur trioxide over from about 20 to about 80%, preferably from about 25 to about 50%, of the remainder of the length of the reaction zone.