The presence of a ternary alloy as well material in InxGa1-xAs/GaAs(001) strained quantum wells introduces a disorder mechanism by which the optical selection rules for symmetric wells may be relaxed and forbidden transitions usually appear in optical spectra. Strain and alloy disorder are studied as a function of well thickness and indium concentration in noninteracting double quantum wells of InxGa1-xAs/GaAs(001). Optical spectra are compared with an accurate Wannier exciton model. The agreement between theory and experiments points out that the optical selection rule for symmetric wells is restored in “high quality” and rather thin quantum wells. Finally, the presence of forbidden transitions in optical spectra is used as a fingerprint of nonhomogeneous indium concentration in thick quantum wells. This property is promising in order to study indium composition for well thicknesses in the range of quasi-two-dimensional behavior of the Wannier exciton. © 1998 American Institute of Physics.