Hydrodynamic characterization of fluidized beds is vital to many industrial processes, including the production of biofuels, pharmaceuticals, and numerous petroleum products. Local time-average phase fractions can be quantified in these multiphase three-dimensional systems using X-ray computed tomography (CT). This paper describes repeatability and uniformity measurements in a 3D 15.2 cm diameter cold flow fluidized bed using CT imaging to quantify gas holdup. Two different bed materials and a range of superficial gas velocities are investigated. Five tests over different days are completed to show repeatability for each test condition. Highly repeatable local time-average gas holdup is recorded at various locations within the bed for each material over all flow conditions. Uniformity is determined by analyzing the local time-average gas holdup at 12 azimuthal locations for both materials and various flow conditions. Uniform axi-symmetric fluidization is observed for each material and Us when the bed height is greater than h = 0.25D, where the effects of individual aeration holes dissipate. (C) 2011 Elsevier B.V. All rights reserved.