In heterogeneous catalytic processes, the relationship between bubble size and various process parameters is important in determining interfacial area, hence mass transfer rate. This paper presents the results of an experimental study of bubble sizes in air-alcohol dispersions with and without the presence of catalyst particles in a batch stirred reactor at different agitation speeds and mean specific energy dissipation rates. Factors investigated include catalyst type, particle size and concentration. It has been found that: Since there are large differences in the viscosity of the various alcohols used, by dividing them into two groups based on the flow type (turbulent or transitional), a consistent correlation has been found for mean bubble size as a function of Weber number, We, for each region, though neither correlation agrees with the precise relationship suggested by Kolmogoroff's theory of locally, homogeneous, isotropic turbulence. At the same We number, the size is bigger in transitional flow than in turbulent. The functionality of the correlation of d(32)/D versus We is similar whether particles are present or not. In fully developed turbulent flow, the bubble size is slightly reduced when catalyst particles are present, independent of catalyst size or type. In transitional flow, the effect of catalyst particles on bubble size is much stronger, the size being reduced by approximately 30%. (c) 2005 Elsevier Ltd. All rights reserved.