The kinetics of butane oxidation by a vanadyl pyrophosphate (VPO) catalyst were analyzed from reduction transients using a novel oscillating microbalance reactor. The reduction rate of the equilibrated VPO catalyst with butane is 0,4th order in the butane concentration and 4th order in the available lattice oxygen concentration. This rate law is effective in representing the reduction of the catalyst to an extent equivalent to the removal of several layers of lattice oxygen. The activation energy for the reduction process is 85 kJ/mol, nearly the same as the apparent activation energy for the steady-state oxidation of butane on the VPO catalyst. These results suggest that the activation of butane is the rate-determining step for butane oxidation on VPO catalysts and that four surface oxygen ions may be involved in this step. The kinetics of VPO reduction by butane are useful in predicting the oxygen capacity of the catalyst and rate of butane oxidation under cyclic feed conditions, as in the circulating fluidized bed process. (C) 2000 Academic Press.