Silicon wafer users must often test non-ideal one-side polished slices for oxygen content. This data is usually biased with respect to the true value. However, this bias can now be eliminated for some types of one-side polished wafers by using calibration programs that are provided with most commercial FTIR instruments. These programs require a calibration wafer of known oxygen content and with a thickness and a backside surface similar to those of the unknown. The effectiveness of this procedure for eliminating bias for several non-ideal sample types is described.