Photoluminescence (PL) and optical absorption studies have been performed on strained-layer InAsxP1-x/InP (001) (x≪0.27) multiple quantum wells grown by low pressure metal-organic vapor phase epitaxy. The series contains samples with both coherently strained and partially relaxed multilayers, where the relaxation is characterized by misfit dislocations. The PL transition line shape at low temperature and at low excitation intensity as well as the evolution of its peak energy with temperature are characteristic of the recombination of band tail localized excitons induced by potential fluctuations. The redshift of the PL peaks relative to the absorption peaks is attributed to two factors: band tail localization and thermalization. The low temperature PL spectra were fitted with an analytical model for the emission line shape, proposed by Ouadjaout and Marfaing [Phys. Rev. B 46, 7908 (1992)]. This allowed us to quantify the PL peak redshift due to band tail localization. After accounting for this effect, the residual energy difference, which we define as the Stokes shift, shows a very strong correlation with the degree of structural relaxation in the multilayers measured by high resolution x-ray diffraction and transmission electron microscopy. This allows the separation of the strain release contribution from the thermalization processes responsible for the Stokes shift. © 1998 American Institute of Physics.