A new type of oxygen sensor is proposed with an ion-sensitive film of V2O5 on an optical waveguide surface and is characterized using prism-film coupling. Upon exposure to excess oxygen in ambient air, the light (lambda = 632.8 nm) transmission through the guide alters due to the change in the refractive index of the film, changing the effective index of the guide. The excess O-2 concentration varies from 50 ppm to few per cent (5%). The influence of the cladding thickness (150-490 nm) and the length (2-6 mm) on the sensor performance are studied. The increase in cladding length enhances the static sensitivity, while the increase in the thickness causes a reduction in the static sensitivity, unaffecting the incremental sensitivity. The performance is identical with static and incremental methods, The response and recovery times are found to be 4-6 and 8s, respectively. An air ambient sintering of the films gives practically a linear response compared to nonsintered films. The sensors are tested for other gases, namely H-2 and H2O, does not show any response except O-2.