Abstract: An impeller assembly for agitating a fluid contained in a vessel and dispersing a gas introduced therein. The impeller assembly includes an impeller having a plurality of generally radially extending blades. Each of the blades includes diverging upper and lower sheet-like portions having generally radially extending leading edges. The upper and lower portions are joined to form a generally V-shaped cross-section with a trailing vertex. The width of the upper portion of each blade is greater than the width of the lower portion of the blade such that the upper portion leading edge extends forwardly of the lower portion leading edge, thus producing an upper portion overhang to capture and disperse rising gas bubbles. The impeller assembly further comprises a drive assembly for rotating the impeller assembly.