The hydrolysis of COS using gamma-alumina as catalyst at 20degreesC is described and discussed. In particular, the effect of calcination on the catalyst activity is investigated. Catalysts calcined at 100 and 500degreesC are found to give the highest catalyst activities, in terms of both specific (mol COS converted/g catalyst/h) and intrinsic (mol COS converted/m(2) catalyst/h) activity. Calcination at other temperatures leads to diminished catalyst activity. The effects are discussed in terms of the known surface chemistry of gamma-alumina involving physisorbed water, surface dehydroxylation and defect formation. The addition of alkali additives (Li+, Na+, K+, Cs+, Mg2+, Ca2+, Ba2+, Si2+) is also reported. Only K+ and Cs+ give a sustained enhancement in catalyst activity, whereas all the other additives act as catalyst poisons for the steady-state performance measured following 5 h time-on-stream. Interestingly, addition of Na+ and Mg2+ leads to a very high initial activity (> 95% COS conversion) but the effect is very short-lived and, after 5 h time-on-stream, a much lower steady-state activity (similar to15-30% COS conversion) is observed.