The nature of gas streaming in a deep fluidized bed containing Geldart's Group A powder has been investigated in a 30-cm ID cold flow unit. Pressure fluctuations have been measured at 8 locations from 4 to 150 cm above the gas distributor for bed depths and gas velocities ranging from 0.4 to 1.6 m and 0.04 to 0.20 m/s, respectively. In order to study the effect of fines content on gas streaming, two particle size distributions with Sauter mean diameters of 48 and 84 mu m were tested for each bed depth and gas velocity. Two distributor plates with differieng percentage open area were also tested for their influence on gas streaming. Analysis of pressure fluctuations in the time and freuency domains, in combination with visual observations show that streaming flow emerges gradually at bed depths greater than 1 m. Increased gas velocity and fines content act to delay the onset of streaming, but cannot completely eliminate it over the range of velocities examined. The two different distributor designs had no measurable effect on the streaming flow. (C) 2010 Elsevier Ltd. All rights reserved.