A probe was developed to isolate and measure the effective particle phase normal stress, or solid pressure, in gas-solid flows. Measurements of solid pressure were obtained in a laboratory-scale bubbling fluidized bed for Geldart Group A, B, and D particles for a variety of flow conditions. The variations of time-averaged solid pressure with superficial gas velocity were examined to characterize the solid stress behavior for the bubbling bed and packed bed regimes, and to determine the minimum fluidization point. Various statistical quantities were calculated from the transient solid pressure data to characterize further the state of the fluidized bed. Solid stress constitutive relations derived from the application of dense gas kinetic theory to particulate flows were used along with the experimental results to obtain values for the effective solid shear viscosity in the bubbling regime. The calculated solid viscosity values were compared with previously reported values (measured by different means) for bubbling beds.