Carbonyl sulfide (COS) from a COS-containing stream (106) is convened in a Claus plant (100) to elemental sulfur (152, 162) by oxidation of a first portion of the COS-containing stream to SO.sub.2 and by hydrolysis of a second portion of the COS-containing stream to H.sub.2S. In preferred aspects of the inventive subject matter, hydrolysis and/or oxidation of the COS is performed in the reactor furnace (10), while hydrolysis of the COS is performed in the reactor furnace (10), a hydrolysis reactor, and/or a catalytic converter (120, 130, 150).