In this study the erosion of poly(ethylene tetrafluoroethylene) (ETFE) (Tefzel) by hyperthermal atomic oxygen (AO) has been examined using X-ray photoelectron spectroscopy (XPS). Initially, the Tefzel film had F/C and O/C atom ratios of 0.74 and 0.04, which decrease to 0.17 and 0.01, respectively, after a 2 h exposure to a flux of 2 x 10(15) atoms/(cm(2) s) AO with an average kinetic energy of 5 eV. The F/C atom ratio is further reduced to 0.02 with longer AO exposures, essentially producing a graphitic or amorphous carbon-like layer with a carbon content greater than 90 at. %. Longer AO exposures do not alter the composition of this layer significantly. Exposure of the AO-damaged surface to O-2 or air nearly doubles the oxygen content in the near-surface region. This is due to dissociative oxygen adsorption at reactive sites formed at the polymer surface during AO exposure. Further exposure to AO removes this chemisorbed oxygen. C-H bonds are important sites for attack during erosion by hyperthermal AO.