Several investigators have attempted to analyze the performance of the ejector on a one-dimensional basis. Some doubt exists whether such analyses can lead to a rational ejector design because of the questionable validity of certain necessary assumptions. Recently, consideration has been given to the two-dimensional aspects of the problem, and while a rational design has not yet been evolved, the results attained seem to point in the right direction. The theory of turbulent mixing in jets, developed by Tollmien is used as the basis of the study reported in this paper. Tollmien’s analysis of the mixing zone produced by a homogeneous air stream issuing into still air of the same pressure and density is reviewed. The authors then extend the theory to allow for the possibility that the driving and driven fluids may have widely different densities.