A simple rapid method of measuring gas viscosity using a standard Fleisch pneumotachograph and a 3-liter hand-driven syringe is described. Comparison of pneumotachographic and predicted viscosity of five pure gases (CO2, N2, He, O2, and Ar), two binary mixtures (He-O2 and N2-O2), and one quaternary mixture (He-air) gave an overall coefficient of correlation of 0.987 and an accuracy of better than 1.7%. Our data show the well-known marked curvilinear relationship between viscosity and the concentration of helium in air and oxygen mixtures. These studies indicate that a Fleisch pneumotachograph can be used as a simple accurate gas viscometer to characterize gas mixtures in terms of viscosity.