In this work, suspension of ultrahigh concentration solids in the presence of gas at different solids concentrations, gas flow rates, and impeller types was studied in a mechanically agitated vessel. A term defined as the power efficiency factor (epsilon(-1)(jsg) (kg/W)) serves as an indication of the quantity of particles that could be suspended per unit of power consumed by the impeller. Accordingly, it was found that the epsilon(-1)(jsg) values can be maximized by operating the mixing tank with an optimum range of solids concentration, which is given as C-v approximate to 0.2-0.3 (v/v) for the systems studied in this work. It was observed that large mixed flow impellers were more energy-efficient when the tank was operated under aerated conditions with an optimum concentration of solids. A mathematical model was developed to predict the impeller specific power epsilon(jsg) (W/kg), which can be used to determine the optimum solids concentration in three-phase stirred vessels, and its predictions exhibited reasonable agreement with the experimental results.