The use of optical sensors for oxygen measurement is becoming more important because of their capability for low-cost and direct measurement, but as yet, little has been reported about their long-term performance. Phosphorescent sensors based on platinum octaethylporphyrin (PtOEP) embedded in polymer matrices tend to degrade with time. To reduce the rate of degradation, sensor films were fabricated and then coated with a layer of polydimethylsiloxane (PDMS) and tested in a six-month study. The PDMS-coated sensors showed an average degradation rate of ~0.073 %/day, compared to ~0.18 %/day for uncoated sensors. Titania beads were also incorporated into the films to increase light scattering and improve the response; these beads compensated to some degree for the absorption due to the PDMS films. The films with titania beads improved the response significantly (about 40%) compared to the films without titania beads. Incorporation of titania beads also moderately improved the aging characteristics.