This article deals with calculation of the mixing action of gas introduced close to the bottom of vessels containing viscous liquids (> 10 mPa s). The mixing time required for 95% mixing was determined. This time decreases with increasing volume flow of gas and level of liquid, increasing eccentricity of the point of gas introduction, and decreasing liquid viscosity. With the aid of an analytical model based on fluid dynamics, the mixing time to be expected can be predicted up to - and presumably beyond - a viscosity of 350 mPa s. Only a slight increase in mixing time is to be expected with decreasing interfacial tension and in systems with inhibited coalescence. The results show that gas-induced mixing of vessels [1-4] is also applicable to high-viscosity liquids. The approach can also be used for purposes other than admixture of reaction stoppers, such as the admixture of additives in normal operation of reactors and storage tanks.