This work presents both theoretical and experimental studies about the specific influence of viscosity, surface tension and density in the formation of a gas bubble. The theoretical model includes both bubble formation and free rising and extends some previous work. As the previous bibliography provides rather scattered data regarding the effect of the liquid properties on bubble generation times, the results can be considered a step forward in the understanding of the subject because they separately describe the influence of viscosity, surface tension and density. The model yields satisfactory results of bubble shapes and formation times when compared to the experimental high-speed video observations obtained using non-Newtonian solutions of carboxymetyl cellulose in water at different concentrations (0.4-1.6% w/w). The complete experimental study also includes a range of different gas flow rates (1-10 cm(3)/s) and orifice diameters (1.5 and 2 mm). (c) 2006 Elsevier Ltd. All rights reserved.