Solids flow through a loop seal in a pressurized circulating fluidized bed (CFB) was studied in an experimental setup in which the effects of system pressure, aeration rates in the two chambers of the loop seal, and particle size could be investigated. The results show that the solids flow rate increases with aeration rate as well as the system pressure. However solids are not recycled until the aeration rate reaches a threshold limit. The solids flow rate also increases with decreasing particle size. Reasonable agreement between predicted and measured values of solids flow is obtained using a simplified analysis of loop seal operation based on a pressure balance around the CFB loop and formulated by the authors.