Transients for oxygen molecular mass numbers 32, 34 and 36 are derived which can be used for the interpretation of oxygen isotope exchange data based on measurement of concentrations of O-16(2),(OO)-O-16-O-18 and O-18(2) in the gas phase. Key parameters in the theory are the rate at which oxygen molecules are subjected to the exchange process at the oxide surface, and two stochastic parameters denoting the probabilities for both oxygen atoms of a molecule to exchange with lattice oxygen. Transport of oxygen in the solid oxide is assumed to be fast. It is shown that any particular mechanism for the exchange reaction lends to a constrained version of the general equations. (C) 2001 Elsevier Science B.V. All rights reserved.