Vertical tubes are commonly used in industrial fluidized beds as heat exchanger tubes. In this study, the influence of vertical tube banks on the axial bubble growth in a 145-mm inner diameter (ID) fluidized bed with Geldart B particles is experimentally investigated by means of pressure fluctuation measurement (PFM) and optical probing (OP). The employed tube bank configurations differ in their tube-to-tube spacing, tube diameter, and tube arrangement (square versus triangular). PFM and OP show that immersed vertical tube banks, irrespective of their configuration, significantly reduce the axial bubble growth. The bubble size reduction is even more significant for higher gas velocities (u(0)/u(mf) > 4.6, where u(0) is the superficial gas velocity and u(mf) is the minimum fluidization velocity) as well as if the tube-to-tube spacing is narrow and the tube diameter is small. The tube arrangement (square versus triangular), in turn, does not show any significant differences. Depending on the gas velocity, the ratio of the bubble diameter to the tube diameter and the tube-to-tube spacing is changed. This change invokes a different bubble flow pattern between the vertical tubes and different bubble growth mechanism, which defines the effectiveness of vertical tubes to delay slugging and makes the fluidization smoother.