Gas permeability studies were performed on five fluorinated cellulose ester membranes. Three of the membranes were of a trifluoroethoxyacetate derivative with varying degrees of hydrogen substitution, 0.6, 1.0, and 3.0, as controlled by stoichiometry. The other two samples were octafluoropentoxyacetate derivatives. Initial characterization studies of the materials, Fourier Transform - Infrared Spectroscopy and Differential Scanning Calorimetry, indicated that the degree of substitution (DS) of the samples had a direct effect on the thermal behavior and the permeability of the samples. With the increase in DS, there was a decrease in the glass transition temperatures and an increase in permeability values. These observations are a result of the increase in substituent chain ends which decreases hydrogen bonding and increases free volume. The results of this study indicate that the use of fluorinated cellulose esters as separation membrane is a viable idea. Further studies will assist in determining the ideal substituent type and substituent distribution which will yield a membrane with the most desirable permeability characteristics.