Apparent shear viscosities of gas-fluidized beds result from microscopic forces due to collisions between particles as well as interparticle friction. Estimation of such theological properties is important for the modelling of the hydrodynamics of fluidized beds. In this work, theological measurements for a gas-fluidized bed of glass beads are carried out using an annular geometry. The parameters varied in the study are the gas flowrate in a small range close to the minimum fluidization value, and the particle size. The experiments show that the fluidized bed behaves like a Bingham plastic. The values of the viscosity obtained are in agreement with previously reported values (0.1-2.5 Pa s), and the yield stress is in the range 1-5 Pa. Further confirmation of the Bingham model is obtained from flow visualization experiments, which show the existence of a finite sheared layer with a thickness that is in reasonable agreement with the theoretically predicted value.