Multiple fluidization regimes were studied using X-ray tomography. Geldart B sand particles were used in a 14 cm (ID) column with a dual cyclone return system. Cross sectional solids concentration (phi) was measured and the time averaged (phi) (((phi) over bar) decreased with velocity and axial height except in the turbulent regime where remained constant. Radial profiles of phi decreased to the centre, while all turbulent regime velocities resulted in similar radial 4) profiles. Results confirm the bubbling-turbulent transition velocity (U-c) determined from pressure fluctuations is a reliable quantification technique. The system exhibited slugging behaviour at higher bubbling regime velocities with voids taking on cylindrical shapes. Turbulent regime voids were characterised by elongated cylinders with diameters slightly less than the bubbling regime's slugs or fast fluidization regime's core annulus. Distribution curves of the phi signal indicated a distinct dense phase in the bubbling and turbulent regime with a velocity independent solid concentration. Void velocity analysis suggested that the bubble linking algorithm was unable to detect fast rising voids at higher velocities. (C) 2013 Elsevier B.V. All rights reserved.