Viscosity is an important property of live crude oil used in design and operation of production processes. Eleven widely used empirical correlations for estimating undersaturated oil viscosity were evaluated using measured undersaturated oil viscosity for live crude oils from primary separators of 10 Brazilian oil wells. The oil samples were characterized as paraffinic-naphthenic crudes. The empirical correlations were found to be inadequate to represent the measured data. The better literature models present average absolute percent relative errors of 1.18% and 1.40% but show wider scatter of data. For more accurate estimates of undersaturated oil viscosity of paraffinic naphthenic live crudes oils, a new model based on Eyring theory is proposed, and this model correlates the experimental data with average absolute percent relative error of 0.97%.