The reduced effective masses inInxGa1−xAs/InPquantum wells have been determined as a function of strain (xvalue) and well width by means of magneto-optical methods. Magnetoexcitons have been observed in photoluminescence excitation spectra in the presence of a magnetic field. At higher magnetic fields, the observed magnetoexcitons will asymptotically approach the free Landau levels. From a least square fit, the dependence of the reduced effective masses on strain and well width has been deduced. Also, the reduced effective mass including the light hole state has been determined for the tensile strained quantum well structure. ©1997 American Institute of Physics.