In this work, the static sorption technique has been extended to measure the diffusivity as well as the solubility of gases in polymers at elevated pressures. This has been accomplished by operating several static sorption capsules in parallel in order to measure the fractional mass uptake of a gas by a polymer with time. Equilibrium and diffusion data of propylene and ethylene in atactic polypropylene have been measured in the temperature range of 25-70 degrees C. The group-contribution, lattice-fluid equation of state (GCLF-EoS) was used to correlate the equilibria data with a single value of the binary interaction parameter for each of the systems. The Vrentas-Duda free-volume theory was employed to describe the propylene and ethylene diffusivity data. The chemical potential gradient used in the free-volume correlation of the diffusivity data was obtained from the GCLF-EoS.