The minimum fluidization velocities of coal, char, limestone, lime and partially sulphated lime under typical AFBC conditions and at room temperature have been determined experimentally. On fitting the experimental data to a Wen and Yu type equation, the two fitted parameters are found to be highly sensitive to the fitting method used to obtain them. The same occurs with the results of other authors, and different pairs of parameter values fit the experimental data reasonably well. After a statistical analysis based on Monte-Carlo simulations, the most suitable method for fitting the experimental data from these studies has been selected. With this method, parameters for use in the Wen and Yu equation for u(mf) under AFBC conditions have been obtained.