Abstract A static technique was used to investigate the surface interaction between CO and oxygen on various Co 3O 4 catalysts at 125 °C and a pressure of 2 Torr. The ratio of CO to oxygen in the reaction atmosphere was 2:1. The Co 3O 4 samples were obtained by the thermal decomposition of basic cobalt carbonate in air at 250, 300, 400 and 500 °C. The amount of chemisorbed oxygen in the different solid catalysts was determined iodometrically. The textural characteristics, i.e. the specific surface area, the total pore volume and the mean pore radius, were determined from nitrogen adsorption isotherms measured at -196 °C. The effects of chemisorbed oxygen and the textural properties of various Co 3O 4 samples on their catalytic activity are discussed.