The gas phase holdup and mass transfer characteristics of carboxymethyl cellulose (CMC) solutions in a bubble column having a radial gas sparger have been determined and a new flow regime map has been proposed. The gas holdup increases with gas velocity in the bubbly flow regime, decreases in the churn-turbulent flow regime, and increases again in the slug flow regime. The volumetric mass transfer coefficient (k(L)a) significantly decreases with increasing liquid viscosity. The gas holdup and k(L)a values in the present bubble column of CMC solutions are found to be much higher than those in bubble columns or external-loop airlift columns with a plate-type sparger. The obtained gas phase holdup (epsilon(g)) and k(L)a data have been correlated with pertinent dimensionless groups in both the bubbly and the chum-turbulent flow regimes.