Gas-mixing and bed hydrodynamics associated with the rise of isolated bubbles in gas-fluidized beds of two granular solids are investigated by means of a novel technique. These diagnostics consist of an array of miniaturized zirconia-based oxygen sensors located along the axis of a hot (1123 K) incipiently fluidized bed, in which isolated bubbles of a tracer gas (nitrogen) are injected. Time-resolved oxygen concentrations and relative pressures are recorded at several levels along the bed. It is shown how the response of the sensors array can be related to the concurrent effects of bubble motion, bubble-emulsion phase, mass transfer and interstitial gas flow in the emulsion phase, combined with each other to give rise to the propagation of two perturbations to the basal value of oxygen concentration. Analysis of time-resolved oxygen concentration profiles enables the assessment of: (a) the bubble rise velocity; (b) the gas velocity associated with the interstitial flow; and (c) the interphase bubble-emulsion phase, mass-transfer rate and coefficient. Analysis of the response of sensors located in the splash zone of the fluidization column provides indirect inference of the hydrodynamic patterns associated with bubble bursting at the surface of the bed. (c) 2005 American Institute of Chemical Engineers AIChE J, 52: 185-198, 2006.