A new power correlation for both anchor and helical ribbon impellers in highly viscous Newtonian liquids is proposed on the basis of a physical model developed from an analytical approximate expression for the drag of a plate in viscous liquids bounded by a plane wall. The correlation, obtained by inserting the empirical factor of geometrical variables in the above expression, shows good agreement with experimental data of power consumption of anchor and helical ribbon agitators obtained in this work and other literature.