The characteristics of gas streaming in a deep gas-solid fluidized bed containing Geldart's Group A powder has been investigated in a 30-cm ID cold flow unit. Four different experimental configurations including forced streaming flow, high and low-velocity jetting and natural streaming flow in deep beds were designed and conducted for bed depths and gas velocities ranging from 0.4 to 1.6 m and from 0.04 to 0.20 m/s, respectively. The range of gas velocities corresponds to 10-50U(mf) which covers the bubbling fluidization regime. The effect of fines content was studied using two particle size distributions with Sauter mean diameters of 48 and 84 mu m, corresponding to 20% and 3% fines content, respectively. Analysis results using autocorrelation and power spectral density (PSD) indicated that the natural streaming closely resembles the forced streaming flow at the wall in which flow of gas is also present in the remaining regions of the distributor. Application of supporting secondary jet injection in addition to the primary gas flow enhanced the fluidization quality to some extent, but was not sufficient to provide fully bubbling fluidization throughout the entire bed. Increasing the primary gas velocity from 10 to 50U(mf) was found to reduce the effect of supporting jets. It was found that higher fines content improved fluidization. Wavelet analysis of pressure fluctuations showed that in deep fluidized beds, bubbling activity with the typical dominant frequency coexists with the streaming flow, however with a minor contribution to the overall fluidized bed behaviour compared to the prevailing streaming flow. Based on the coexistence of several bubble streams in a bubbling fluidized bed as reported in the literature, Wavelet findings suggested that the streaming flow can be considered to form by increasing the relative importance of one of the available streams of bubbles with increasing bed depth. (C) 2010 Elsevier B.V. All rights reserved.