This paper describes the application of a technique based on luminescence quenching to measure the diffusivity and permeability of molecular oxygen in a series of poly(n-alkylaminothionylphosphazenes) (CnPTP) and in un-cross-linked high molecular weight PDMS. The glass transition temperatures (T-g) of these polymers decrease from 4 degrees C for n = 2 to -18 degrees C for n = 6. Experiments performed on thin films of these highly permeable polymers show that oxygen diffusivity is sensitive to the microstructure of these polymers and that the diffusion coefficient for oxygen increases as T-g decreases. In contrast, the oxygen solubility in these polymers is not very sensitive to the nature of the alkyl substituent. Both the oxygen diffusion coefficient D-O2 and the oxygen solubility S-O2 are smaller for this series of polymers than for PDMS.