Two- and three-phase systems have been studied using particles that are water-wetted and denser than water and with similar sized, small floating particles, both wetted and non-wetted. The parameters investigated have been the agitator speed required to disperse the different types of particles under sparged and non-sparged conditions and rates of gas-liquid mass transfer. With the wetted, dense particles, only at concentrations of > similar to20% w/w did the k(L)a fall significantly (by similar to20 to 30%) whilst solid suspension followed the trends of earlier work. With the less dense particles, even with < similar to1% w/w that were not wetted, it was very difficult to disperse them throughout the liquid phase, though up-pumping impellers were more effective than radial. In addition, bubble size significantly increased and kLa fell by a factor of 2 to 3. With the wetted, less dense ones up to 2% w/w, uniform dispersion was achieved even at much lower speeds and k(L)a did not change compared to the case without solids.