Here, an in situ curvature relaxation (kappa R) method was used to measure chemical oxygen surface exchange coefficients ((k) over tilde 's) under well-characterized stress, temperature, and oxygen partial pressure conditions. These (k) over tilde 's were measured by analyzing the transient curvature of yttria stabilized zirconia supported La0.6Sr0.4FeO3-delta thin films reacting to oxygen partial pressure step changes. The sputtered thin film (k) over tilde 's measured here were consistent with extrapolated bulk sample (k) over tilde 's, but larger than those reported for pulsed laser deposited thin films. This is the first time that the curvature response of a system has been used to characterize thin film oxygen surface exchange kinetics. The simultaneous measurement of film stress and (k) over tilde provided by the curvature relaxation method may help explain the large k discrepancies observed in the literature. (C) 2013 Elsevier B.V. All rights reserved.