Empirical equations for predicting the viscosity of Iranian crude oils above, at and below the bubble-point pressure were developed based on pressure-volume-temperature (PVT) data of 57 bottom hole samples collected from central, southern and offshore oil fields of Iran. Both statistical and graphical techniques were employed to evaluate these equations compared with other empirical correlations. The results show that the developed correlations present better accuracy and performance for predicting the viscosity of Iranian crude oils than those correlations in literature.