Much controversy exists in the literature about the effects of different variables on the onset of the turbulent regime in gas-solid fluidization, U-c, and on the transport velocity, U-tr. In order to study the effect of four hydrodynamic factors upon these transition velocities, a basic 8-run Plackett-Burman design was used. The factors and their level were : (a) diameter of column (82 vs 200 mm), (b) particles (FCC vs Sand), (d) static bed height (300 vs 450 mm) and (g) size distribution of particles (narrow vs wide). In each run, U-c and U-tr were determined experimentally by means of differential pressure transducer and also with a capacitance probe. The experimental results and statistical analysis show that bed diameter has the most important impact (61% variability upon U-c and 51% upon U-tr). The product of particle size and density (p(p)d(p)) seems to have a significant effect (35% variability upon U-c and 47% upon U-tr). Static bed height has a slight impact. There is essentially no effect of the particle size distribution. Results show that interactions effects are negligible between these factors. Finally, two correlations for U-c and U-tr, which are in agreement with literature data are proposed.