The influence of organic additives (propanol, benzoic acid, isoamyl alcohol and carboxymethylcellulose) on the volumetric mass transfer coefficient, k(L)a, in an internal loop airlift reactor with low-density particles (nylon-6 and polystyrene) was investigated. The k(L)a values increased with increase in superficial gas velocity, U-sg, and decreased with increase in solid loading. A draft tube to reactor diameter ratio, D-R/D, of 0.4 gave maximum k(L)a values. The addition of benzoic acid and propanol increased the k(L)a values owing to their coalescence inhibiting characteristics. The addition of isoamyl alcohol decreased k(L)a, owing to the formation of rigid bubbles and recirculation of small bubbles having a low oxygen content. The k(L)a values decreased with increase in the concentration of the non-Newtonian fluid carboxymethylcellulose (CMC). The proposed correlations predicted the experimental data well. (c) 2006 Society of Chemical Industry.