An experimental study of the influence of pressure on fluidization phenomena was carried out in a bubbling fluidized bed over the range of operating absolute pressures 101-2100 kPa with Geldart A and B bed materials in an apparatus 15 cm in diameter. Bed voidage data was gathered using electrical capacitance tomography (ECT) and the resulting time series were analysed to give average bed voidage, average absolute deviation, average cycle frequency and Kohnogorov entropy. Bed collapse tests were also performed to establish the influence of operating pressure on dense phase voidage. For the Geldart B powder U-mf was found to decrease slightly with pressure whilst voidage at U-mf was unaffected and no change in behavior from Geldart B to A was observed. Analysis of the ECT results for the Geldart B powder showed no influence of pressure on cycle frequency and average absolute deviation, but an increase in mean bed voidage with pressure. For the Geldart A powder, no influence of pressure on U-mf, U-mb and epsilon(mf) was observed, though epsilon(mb) was found to increase slightly with pressure. Analysis of the ECT results for the Geldart A powder revealed a decrease in average bed voidage, cycle frequency and average absolute deviation with pressure. The trend in Kolmogorov entropy within increasing pressure was not entirely revealed over the range of velocities used, but results suggest a decrease. (C) 2004 Elsevier B.V. All rights reserved.