Experiments were conducted to determine the effects of impeller clearance, impeller diameter, and other operating variables on the minimum agitation speed for off-bottom solid suspension in agitated vessels, N-js for disc turbines (DTs) and flat-blade turbines (FBTs). Only data for which the impellers produced recirculation flows above and below the impeller (the so-called "double-eight" flow pattern) were considered Regression equations for N-js were obtained, in which explicit terms for impeller clearance and vessel diameter-to-impeller diameter ratio (T/D ratio) were included. Modified Zwietering equations (Zwietering, 1958) were also obtained, in which Zwietering＇s parameter S was mathematically expressed as a function of vessel diameter-to-impeller clearance ratio and T/D ratio. When used together with the correlations of Armenante and Uehara Nagamine (1998) for impellers close to the vessel bottom, the equations presented here can be used to calculate N-js for DTs and FBTs for any typical impeller clearance.