This paper compares invasive and non-invasive voidage measurement techniques from five different Canadian laboratories for the determination of local voidage profiles in gas-fluidized beds of 104 mu m Fluid Cracking Catalyst (FCC) and 332 mu m silica sand in a column of 133 mm id. A novel modular system and auxiliary components were designed and constructed to facilitate transportation to, and deployment at, different research centers. Profiles of time-averaged voidage were determined by optical fiber probes, dynamic pressure measurements, electrical capacitance tomography, X-ray computed tomography and radioactive particle tracking by researchers from different research groups. These results are compared with average measurements from pressure gradients and overall bed expansion. Results were kept separate from each other in a double-blind method. There is general, but imperfect, agreement among the different methods for average voidage for both the FCC and silica sand. Invasive probes gave similar results and scatter to non-invasive techniques. (C) 2012 Elsevier B.V. All rights reserved.