The bubble characteristics have been investigated in an air-water bubble column with shallow bed heights. The effect of bed height, location and the presence of solids on the bubble size, bubble rise velocity and overall and sectional gas holdup are studied over a range of superficial gas velocities. Optimal shallow bed operation relies on the combined entrance and exit effects at the distributor and the liquid bed surface. The gas holdup is found to decrease with an increase in H/D ratio but the effect is diminishing at high H/D ratios. A H/D ratio of 2-4 is found to be suitable for shallow bed operation. The presence of solids causes the formation of larger bubbles at the distributor and the effect is diminishing as the gas velocity is increased. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.