Abstract : An experimental investigation of the turbulent mixing of two dissimilar gases for both subsonic and supersonic flows is presented. This investigation was carried out in order to determine the turbulent transport coefficients for hydrogen-, helium-, and argon-air mixtures in the mixing region of two coaxial jets. The basic differential equations describ ing the mean flow properties are solved for the transport coefficients. The convective derivatives which are needed in the solution of the equations are determined from the velocity and concentration profiles measured in the experiments. Values of the eddy viscosity, turbulent diffusion coefficient, and Lewis number were evaluated in this manner and the eddy viscosity so obtained is then compared with existing formulations. A new formulation for the eddy viscosity is then given whereby existing theories may still be used in analyzing the mixing process. Finally, the influence of similar velocity and concentration profiles on the transport properties is discussed and similarity parameters in both axial and radial directions are then shown to be valid for various injected gases. (Author)