The permeation of oxygen through high-purity, large-grain Ag membranes has been studied over the temperature range of 400–800 °C. The permeability was found to be linear and repeatable, but the magnitude was 3.2 times smaller than that determined by past research. This factor may be due to negligible grain boundary diffusion that exists in this work. Auger electron spectroscopy (AES) does, however, suggest the importance of grain boundaries since intragranular oxygen was virtually undetectable and since AES line scans show substantial oxygen signals around the grain boundaries. The diffusivity measurements were found to exhibit two distinct linear regions, one above and one below a critical temperature of 630 °C. The high-temperature data have an activation energy (11.1 kcal mol−1) similar to that reported by others, but the low-temperature data have a comparatively larger activation energy (15.3 kcal mol−1). Vacuum desorption of the oxygen-saturated Ag was found to occur at the critical temperature of 630 °C, which is consistent with the increased mobility of oxygen atoms in the higher temperature regime. The higher activation energy observed in the lower temperature regime is probably due to the higher efficiency of traps.