Computer-automated radioactive particle tracking (CARPT) data obtained in a 0.162 m air-water bubble column operated at ambient pressure have been analysed. The superficial gas velocity (u(g)) has been varied in the range 0.02-0.12 m/s under constant liquid height 1.04 m. A perforated plate (82 holes diameter 0.4 mm, free plate area 0.05 %) distributor has been used. The Kolmogorov entropy (KE) vs. u(g) allows identification of the transition velocity (U-trans = 0.064 m/s) between bubbly and transition regimes. KE models for both regimes have been also developed. The quality of mixedness (QM) concept shows that QM(upper zone) = QM(lower zone) at U-trans = 0.064 m/s.