Spin orientation by optical pumping experiments were undertaken on three strained In0.2Ga0.8As/GaAs QW's with different thicknesses. The results concerning the circular degree of polarization dependence on the exciting energy are very different from well to well. This indicates that in such systems the hole spin relaxation is incomplete and must be considered in the interpretation of the optical pumping data. We show that the complexity of the situation makes difficult the evaluation of the characteristic times governing the photoluminescence polarization.