A process for producing a purified gas stream from a feed gas stream comprising contaminants, the process comprising the steps of: (a) removing contaminants from the feed gas stream to obtain the purified gas stream and a sour gas stream comprising H.sub.2S and RSH; (b) separating the sour gas stream comprising H.sub.2S and RSH into a gas stream enriched in H.sub.2S and a residual gas stream comprising RSH; (c) converting H.sub.2S in the gas stream enriched in H.sub.2S to elemental sulphur in a Claus unit, thereby obtaining a first off-gas stream comprising SO.sub.2; (d) converting SO.sub.2 in the first off-gas stream comprising SO.sub.2 to H.sub.2S in a Claus off-gas treating reactor to obtain a second off-gas stream comprising H.sub.2S; (e) converting RSH from the residual gas stream comprising RSH to H.sub.2S in an RSH conversion reactor to obtain a residual gas stream comprising H.sub.2S, wherein at least one of the operating conditions of the RSH conversion reactor is different from the corresponding operating condition of the Claus off-gas treating reactor.