Piston flow regime in three-phase fluidized beds has been studied for a 10-cm diameter column with 3-mm glass beads at low gas velocities (up to 1.5 cm/s). The effects of distributor type and coalescence inhibitors have been investigated. The piston flow regime can be detected and characterized in frequency and amplitude by conductivity measurements. Such quantification improves on visual observations by allowing for regime detection in industrial columns. The piston flow regime is stronger at low gas velocities and for liquid velocities around the minimum fluidization velocity. The occurrence of piston flow regime depends on the distributor type used and the presence of coalescence inhibitors. The type of distributor most likely to promote this flow regime presents a variable resistance to the gas flow. For certain distributors, piston flow can be observed even in the absence of coalescence inhibitors. Coalescence inhibitors widen the range of gas and liquid velocities over which pistons are observed and increase their amplitude by as much as 100%.