[en] The diffusivity of oxygen in beta-Zircaloy-4 and the isothermal oxidation rates of Zircaloy-4 in steam were determined. Both sets of measurements were made in the temperature range 900 to 1500⁰C (1652 to 2732⁰F), and considerable care was exercised to ensure the accurady of temperature determinations. Diffusivity determinations were made using an ¹⁸O radioactivation technique; supplemental measurements were made by Auger electron spectroscopy and by observations of the movement of (α + β)/β boundaries during diffusion anneals. No differences were observed between tracer and chemical diffusivity values or among oxygen diffusivities determined in zirconium, Zircaloy-2, and Zircaloy-4. Between 1000 and 1500⁰C (1832 and 2732⁰F) the combined data set for the diffusion of ¹⁶O (corrected for mass effects from the ¹⁸O data) was represented by: D/sub β/ = 0.0263 exp(-28200/RT) cm²/s. Oxidation rate curves were determined at 50⁰C (90⁰F) intervals, ten specimens being used to define the curve at each temperature. Above 1000⁰C (1832⁰F) parabolic oxidation behavior was observed; below that temperature, the curves for the rate of growth of the oxide layer were not parabolic. For this reason, statistical evaluation of the data based on parabolic kinetics was limited to temperatures above 1000⁰C except for alpha-layer growth, which followed parabolic kinetics over the entire temperature range. The rate constants were well represented between 1000 and 1500⁰C by Arrhenius relationships