Pulsed-field gradient nuclear magnetic resonance (PFG-NMR) was employed to investigate the velocity distribution (propagator) and dispersion coefficient of a model fluidized-bed reactor of low aspect ratio containing mustard seeds. Both propagator and dispersion were found to be strongly anisotropic due to slug-flow conditions, with the vertical/axial dispersion ratio becoming smaller with increasing air flow rate. The influence of air humidity and flow rate was discussed in the gas-solid system, and the concurrent effect of electrostatic charging of particles close to the reactor wall was shown. Dispersion was generally found to increase with growing humidity and superficial gas velocity. For comparison, results are presented for a gas-liquid-solid system with a water-to-particle mass ratio of 2:1 as a function of bed height. The results indicated that the addition of water enhanced the particle motion in the bed.