The present invention relates to a process and a plant for producing sulfuric acid, in which a starting gas containing sulfur dioxide at least partly reacts with molecular oxygen in at least one contact with at least one contact stage to form sulfur trioxide, and in which the sulfur-trioxide-containing gas produced is introduced into an absorber and converted there to sulfuric acid. To achieve that only small gas volumes must be supplied to the first contact stage, based on the amount of sulfur dioxide used, with at least the same capacity of the plant and by using conventional catalysts, it is proposed in accordance with the invention to supply to the first contact stage a contact gas with a sulfur dioxide content of more than 16 vol-% and with a volumetric ratio of sulfur dioxide to oxygen of more than 2.67:1.