The effect of dry operating conditions upon the oxidation of CO over Co3O4 and Au/Co3O4 has been studied. Under dry conditions (with pretreatment and reaction gases dried at -76-degrees-C using molecular sieve traps) oxidation of CO over Co3O4 can be observed at temperatures as low as -54-degrees-C. However, without sufficient drying Co3O4 rapidly deactivates. On the other hand, the Au/Co3O4 catalyst is resistant to the presence of moisture even at low temperatures. For both the Co3O4 and Au/Co3O4 catalytic systems, strong and periodic oscillations in percentage conversion and catalyst bed temperature have been observed.