Relevant points have to be mentioned for CSP model viscosity. For Oils 1, 7 and 8 the employed model exhibits statistical violations (credible regions do not cover all experimental data). Such violations occur mainly in the relatively low pressure regions of the experiments (below 100 bar). These regions also show a large uncertainty range and curve slope variations. A possible explanation is that when pressure decreases, light hydrocarbon components leave liquid phase increasing the fraction of heavier components in the liquid phase. Thus, liquid phase becomes more dense and possibly exhibits a behavior closer to Non-Newtonian, in which heavy oil CSP viscosity model is not appropriate . This interpretation is clarified due to the Credible Region provided by the Bayesian approach, which is not present in classical deterministic regressions.