A theoretical equation and empirical data (Skelland and Ramsey, 1987; Yamamura and Takahashi, 1999) were compared to estimate the minimum impeller speed for liquid-liquid dispersion in mechanically agitated vessels. Skelland s geometrical constant S was correlated by the following equation. S = K/N-p(1/3) (D/d)(alpha)(H/D)(alpha-2/3) [1 + beta(s/H - gamma)(2)] The values of alpha, beta, and gamma were 1.51, 3.61, and 0.483 for radial flow impellers (disk turbine, curved paddle and flat paddle), and 1.31, 4.08, and 0.444 for axial flow impellers (pitched paddle and marine propeller). The value of K was 1.46 for radial flow impellers and 1.84 for axial flow impellers based on the conductivity method. The minimum impeller speeds measured visually depend on the definition of complete dispersion.