BACKGROUND: Investigations of hold up (epsilon(g)) and interfacial area (a) in cylindrical bubble columns have been reported extensively but reported similar investigations in tapered bubble columns are sparse in the existing literature. Thus the current article reports the experimental determination of epsilon(g) and a using a tapered bubble column. RESULTS: The present system generated epsilon(g) (0.556 to 0.641) in a CO2-NaOH system 20% higher than in an air-water system (0.466 to 0.534) and values were higher than in existing systems. Also, the values of epsilon(g) in the air-water system were higher than reported for a column with shorter tapered angle. Values of epsilon(g) fitted very well with the well-known Akita and Yoshida correlation. The observed values of a (235 and 700 m(2) m(-3)) were higher than values obtained (2 to 600 m(2) m(-3)) in existing systems. The energy dissipation was 203 to 335 W m(-3), which was lower than that (100 to 1200 W/m(3)) in existing systems. A correlation developed to predict the pressure drop in terms of Euler number was statistically highly significant. CONCLUSION: The present research achieved higher values of hold up and interfacial area, and lower values of energy dissipation per unit volume of dispersion compared with existing systems. Findings of the present study coupled with previous studies indicate that the tapered bubble column developed could find potential application not only in air pollution control but also in gas-liquid mass transfer operations. (C) 2011 Society of Chemical Industry