Experiments were performed in air-water and air-water-glass particles systems to study variations in gas holdups, bubble population and their rise velocities. Slurry concentrations up to 40% (v/v) and superficial gas velocities up to 0.30 m/s were investigated. The measurements were made using fast response pressure transducers and the dynamic gas disengagement (DGD) technique. The gas holdup due to small bubbles decreased with increasing slurry concentration up to slurry concentration of 25% (v/v), but increased slightly at higher slurry concentrations. The gas holdup due to large bubbles decreased slightly with increasing slurry concentrations. The rise velocity of larger bubbles increased with slurry concentration up to about 20% (v/v) and reached an asymptotic value for higher slurry concentrations. The rise velocity due to small bubbles increased at a much faster rate with increasing slurry concentrations but passed through a maximum at slurry concentration of about 25% (v/v) before dropping at higher slurry concentrations. The drop in rise velocity of smaller bubble fraction is attributed to accumulation of fine bubbles in the suspension at high slurry concentrations and gas velocities used in this study.