Reflectance and photoluminescence spectroscopy have been used to study the optical properties of high quality InxGa1-xAs/GaAs (0.13≤x≤0.30) single quantum wells. The results show strong agreement with the theoretical model used taking into account the strain potential. The agreement of the theoretical model, though, deviates from the experimental results for large values of excess strain in the well. For the case of the large strain (x=0.30) the reflectance indicates the strain in the well is hydrostatic rather than biaxial. The relevance of this fact is discussed in relation to device performance.