The invention relates to a process for oxidation of SO2 to SO3 comprising the steps of (a) directing a stream of feed gas comprising SO2 and O2 to a catalytically active material, (b) oxidizing an amount of said SO2 in said process gas to SO3 in the presence of the catalytically active material, providing a first oxidized process gas, (c) reacting SO3 with water, (d) condensing H2SO4, (e) withdrawing a first desulphurized process gas and a first stream of sulphuric acid, (f) from the desulphurized process gas withdrawing a recycle stream of desulphurized process gas, wherein the recycle stream is added to said stream of feed gas or said first oxidized process gas with the associated benefit of reducing the molar flow of process gas downstream withdrawal of the recycle stream and upstream the mixing point.