The free liquid surface of the binary system has been studied by reflection ellipsometry in the temperature range below and near the upper miscibility gap. The ellipticity of samples of concentrations below and above the critical composition was measured as a function of temperature T and compared with calculations of based on model refractive-index profiles. The pronounced increase of with T at concentrations is consistent with a model profile that entails there being a water-enriched layer just below the surface. The thickness of this water-rich layer increases as one approaches the phase-separation temperature, as is to be expected for preferential wetting of the surface of the concentrated micellar solution by the coexistent dilute micellar solution.