Different methods of response data analysis in the time and frequency domain were compared in a study of local and overall liquid mixing properties of a gas-liquid-solid internal loop airlift reactor with low density particles. The reactor was analysed using the axial dispersion model as a system consisting of five interrelated zones : draft, annulus and three top sections. Convolution in the time domain was the simplest and most accurate method of response data analysis, based on the predictions of the mean residence time. This method requires an analytical solution in the time domain of the non-ideal flow model. In cases when such a solution is not available (e.g. for the air Lift reactor as a whole), analysis in the frequency domain was used with almost the same results.