A resume of the current state-of-knowledge concerning rarefied gas flow through passages with static boundaries is presented. A brief development of the theoretical gas flow models which have been used for long tubes and annuli is included. These theoretical models have been developed to cover the flow regime extending from laminar continuum flow to free molecular flow. The analysis required to use these models is simple and straightforward. Experimental data are presented for the flow of argon through a long tube and for the flow of argon and xenon through annuli. The experimental values of mass flow rate per unit pressure drop as a function of Knudsen number are graphically presented for a long tube and for two annuli. Also presented on the same figures are the values predicted by the theoretical models. The agreement between theory and experiment for the complete regime between continuum and free molecular flow is very good.Presented at the ASLE Annual Meeting in Cleveland, May 6–9, 1968.