Estimation of rock type, porosity and saturation are the main applications of petrophysical logs. Several equations are presented for mentioned estimations, and deficiencies of these equations are widely investigated. In this paper, general deficiency of well logs processing methods is discussed. In general, because of smoothing trait of estimators, variability of estimated data is less than raw data. Since rock type, porosity and saturation are estimated from various well logs, it is anticipated that they have less variability in comparison with raw well logs. Therefore, it seems that energy (equal to information) of Fourier transform of estimated well logs in low frequency bands have to be more than similar energy of raw well logs. This study has been done on raw and estimated well logs of more than 100 wells of Iranian south and southwest oil fields. The results showed that estimated well logs have more variability, which confirms a fundamental deficiency in current well log processing methods.