The d.c. conductivity, sigma, and the oxygen gas-sensing behaviour of V2O5-SnO-TeO2 glass prepared by press-quenching were studied in argon and oxygen gas atmospheres at temperatures ranging from 303-473 K. The glass of 50V(2)O(5).20SnO.30TeO(2) (mol %) was n-type semiconducting. The high-temperature conductivity was lower in oxygen and higher in argon than that in air. This was explained by the V4+ ions in the glass being oxidized by oxygen which had diffused into the glass, resulting in an increase in V5+ With time. The experimental relationship between sigma and oxygen partial pressure, P-O2, agreed quantitatively with the theoretical relation sigma proportional to p(O2)(-1/4). Changes in conductivity by switching the atmospheres between oxygen and argon gases were found to be reproducible. From the data of these dynamic changes, the oxygen gas sensitivity, S, at 473 K was obtained to be 1.3 in oxygen atmosphere. The dynamic changes could be quantitatively explained by an oxygen diffusion model. Throughout these discussions, the present tellurite glass was found to possess a potential applicability as an oxygen gas sensor.