Methane activation at 450-700 degrees C by 14 mol% calcia-stabilized zirconia was studied by the transient reaction of pure methane with the oxidized material. Three distinct sequential reaction regimes are observed. Initially, methane oxidation rates are similar to those in cofed methane-oxygen mixtures. After a small amount of oxygen (amount) is removed from the material, the reactivity of the material suddenly increases while a larger amount of oxygen, roughly equivalent to 1 surface layer, is removed. Finally, after this reductive phase, methane continues to react rapidly to deposit a surface layer of carbonaceous material which can be removed by reoxidation. This cycle can be repeated.