A process for fractionating a starting mixture of two or more components by extractive distillation using a selective solvent in a dividing wall column aligned in the longitudinal direction of the column and extending to the upper end of the column and dividing the column interior into a first region, a second region, and a lower combined column region. The starting mixture is fed into the first region, a first top stream is taken off from the first region, and a second top stream is taken off from the second region, each stream having a prescribed specification. The selective solvent is introduced in the upper part of the first region and/or in the upper part of the second region, and solvent flow into the first region and/or solvent flow into the second region are set so that each of the prescribed specifications for the top streams are met.