Reactive sputtering has been investigated by a number of workers, but no clear, generalized picture of the method or the phenomena involved has emerged. It is shown that the variation observed in the partial pressure of O2during both reactive and nonreactive Ta depositions is a sensitive measure of reactive surface activity in the plasma. A detailed examination of the O2behavior is made as the degree of activity of either target or substrate is systematically changed. A correlation is made between observed O2partial pressure variations and resulting compositional variations of the collected films using Auger electron spectroscopy, Auger sputter profiling, and transmission electron microscopy. Most importantly, we describe the reactive sputtering of Ta in O2in terms of two inverse reactions at two reactive surfaces; a dissociative reaction proceeds at the target while its inverse proceeds at the substrate. A generalized process in which a metal oxide dissociates to a less‐stable suboxide at the target, transfers to the substrate as the suboxide, and recombines to form the original target compound, is suggested for the reactive sputtering of any metal oxide which exhibits preferential sputtering effects.