The results of a series of studies are reported in which the added mass experienced by a 25 mm sphere oscillating in two-phase systems consisting of bonded spheres in various liquid media is measured in a variety of configurations using a remote drive vibrating reed technique. The arrangements considered investigate the effects of surface roughness and bed voidage together with variations in fluid density and viscosity expressed in terms of the Stokes number in the range of 4.5-110. The results are then correlated in terms of simple mathematical expressions for the subsequent prediction of added mass as a function of the above parameters.