<p>Graphene oxide (GO), as a 2D membrane, exhibits outstanding molecular sieving properties for gas separation. The gas permeation mechanism in GO sheets is quite different from that of traditional polymer membranes due to their multilayer nature. It is still a challenge to directly and accurately measure gas diffusion coefficients in ultrathin multilayer membranes. In this work, we applied a well-proven experimental method to determine the diffusivities for H₂, He, CH₄, N₂, O₂, Ar and CO₂. Unlike polymer membranes, the diffusivity for all gases in 2D membranes depends exponentially on the path length and diffusing time. This study is important for both characterizing and standardizing the gas transport properties of thin GO sheets, designing novel membranes based on carbon materials, and for gas mixture separation or toxic gas removal processes. Some applications of the present investigation are discussed.</p> Graphical abstract <p></p>