Equilibrium sorption and kinetics of acetone, methyl ethyl ketone (MEK), methyl n-propyl ketone (Mn PK), and methyl i-propyl ketone (Mi PK) uptake in uniform, biaxially oriented, semicrystalline polyethylene terephthalate films were determined at 35 degreesC and low penetrant activity. Sorption isotherms for all penetrants were well described by the dual-mode sorption model. Sorption and desorption kinetics were described either by Fickian diffusion or a two-stage model incorporating Fickian diffusion at short times and protracted polymer structural relaxation at long times. Diffusion coefficients and equilibrium solubility at fixed relative pressure decreased in the following order: acetone > MEK > Mn PK > Mi PK. Diffusion coefficients for each penetrant increased with increasing penetrant concentration. (C) 2004 Elsevier Ltd. All rights reserved.