A method and a device for the sulfonation or the sulfation of organic liquid raw materials with an SO3/air mixture and other reaction gases in order to perform rapid, highly exothermic gas-liquid reactions in conventional thin-layer falling-film reactors are disclosed. The introduction of the SO3/air mixture occurs through several feed locations, which are located within (along) the reaction tube or reaction tubes or in the annular gap of annular-gap falling-film reactors. High peak temperatures, undesirable byproducts, worsening of the color and local oversulfation or oversulfonation, which leads to side reactions, are largely avoided.