Acoustic‐wave propagation in gases is studied for the case where the ratio of the transmitter‐receiver separationsto the mean free path Λ of the gas molecules is sufficiently small so that the propagation constant is independent of Λ (free‐molecule propagation). Experimental results, obtained in air and in argon, are found to be in agreement with the existing theories. Free‐molecule propagation is distinguished from ordinary sound propagation that takes place ifs/Λ is sufficiently large in order that the propagation constant is independent ofs. The ranges of free‐molecule propagation and sound propagation are found to be approximatelys/Λ5, respectively.