Abstract. The product compositions in a distillation column depend primarily on the product split D/B, and valuable insight is obtained by considering the effect of various disturbances on D/B. For a given disturbance, say an increase in feed rate F, the effect on D/B is strongly dependent on the chosen control configuration (structure), that is, on the two inputs used for composition control. Configurations where D=B is sensitive to disturbances should be avoided, and this may be used as a valuable tool for selecting column configurations. Presently, the Relative Gain Array (RGA) is the most used tool. The RGA is computed from the process gain matrix and contains no information about disturbances. Yet, for the most commonly used configurations there happens to be a close correlation between large RGA-values and disturbance sensitivity. This correlation gives one explanation for why the RGA actually has proven to be so useful for distillation columns.