We have studied the effect of various controlled surface oxidation treatments on photoluminescence excitation spectra of porous silicon for various emission energies. The UV excitation spectra of fresh samples were found to be peaked with a monotonic relation between peak excitation energy and emission energy, and to have an onset near 3.3 eV, the direct gap of Si. Aging (ambient oxidation) was found to unevenly affect the excitation spectra, resulting in an effective red shift of the peak center. On the other hand, anodic oxidation or oxidation by exposure of the sample to copper ions in solution caused a blue shift of the excitation spectra. These results are explained in terms of surface condition effects on nonradiative loss sites or on the interquantum dot barriers. ©1997 American Institute of Physics.