Results are reported for the one-component permeation of a number of gases through a silicalite-l membrane. The effect of several operating conditions, like the temperature, the feed pressure, the sweep gas flow rate, and the orientation of the membrane; on the Hull are discussed. The optimal experimental conditions are identified for both steady state and transient permeation. Results for the flux as function of the pressure, 10-900 kPa, and as function of the temperature, 200-700 K, are modelled taking two diffusion mechanisms into account. Permeation results are reported for two different silicalite-l membranes. A small difference in the permeance is observed, indicating a high reproducibility of the zeolite membrane synthesis. The contribution of the equilibrium isotherm to the flux and the permeance is demonstrated. A comparison is made between results obtain with helium and argon as the sweep gas. Finally, results are reported for the permeation of pure gases through a silicalite-l membrane modified by silanation.