Apparatus and process for recovering elemental sulfur from a H.sub.2S-containing waste gas stream are disclosed. The apparatus preferably comprises a first reaction zone for carrying out the catalytic partial oxidation of H.sub.2S, a second reaction zone for the catalytic partial reduction of any incidental SO.sub.2 produced in the first reaction zone, and a cooling zone including a sulfur condenser. According to a preferred embodiment of the process, a mixture of H.sub.2S and O.sub.2 contacts a catalyst in the first reaction zone very briefly (i.e, less than about 200 milliseconds) producing primarily S.sup.0 and H.sub.2O. Some SO.sub.2 is also present in the first stage product gas mixture. A reductant gas (e.g. CO, or CH.sub.4 or natural gas) is fed together with the first stage product gas mixture to a second catalytic reaction zone where the partial reduction of the SO.sub.2 component to elemental sulfur and CO.sub.2 is carried out.