High velocity turbulent jets are often used in hydraulic structures to dissipate energy and to induce or enhance airentrainment. Examples include ski jumps and bottom aeration devices. This article presents new air concentration and velocity measurements performed in the flow development region of high velocity water jets. The measurements were obtained using a two-tips conductivity probe. The data are compared with analytical air concentration profiles derived from the diffusion equation, and theoretical velocity profiles of turbulent shear layers. The results highlight that the lower jet interface defined as C = 90% coincides with the streamline of maximum velocity gradient.