This paper describes a series of experimental results in the development of fiber optic oxygen sensor with excellent immunity to quenching by water vapor. The sensor exhibits good oxygen response (4 dB quenching when PO(2) changes from 0 to 190 torr) identically in both 0% and 100% relative humidity environments. To develop this sensor the solution spectra of several organic fluorescent compounds were characterized for oxygen quenching efficiency. The most promising of these fluorophores were coated onto porous substrates using a proprietary process and tested for their sensitivity to oxygen and the potential interference from water vapor. The presence of oxygen quenches the fluorescence radiated by many compounds. Since water is also commonly found to quench fluorescence, a humidity insensitive oxygen sensor would be of great value in most applications. Each of the sensors was characterized for its fluorescence excitation and emission wavelengths, sensitivity for oxygen, and quantum efficiency. The most promising fluorophores, decacyclene and benzo[g,h,i]perylene, demonstrated the best overall results of the compounds tested. These fluorophores were characterized for their response to oxygen, as well as a cross- sensitivity to water vapor, carbon monoxide and carbon dioxide.