The hydrodynamics of countercurrent gas and liquid flows through a trickle bed reactor with unstructured (8 mm Raschig rings) and structured (Bale) packing has been investigated using the residence time distribution (RTD) approach. The operation was carried out with gas and liquid Reynolds number over the range 0 < Re-G < 150 and 0 < Re-L < 1500, respectively. Gas phase Peclet number, Pe(G), was generally higher in the randomly packed Raschig rings than in the structured Bale packing but increased with Re-G. However, gas phase mixing decreased with increasing liquid flow rate. Specifically, the dependency on Re-G and Re-L was given by, Pe(G) = A(G)Re(GbG), exp(-dRe(L)). The gas phase hold-up, H-0G also increased with gas flow rate but decreased with the liquid flow rate. Owing to the statistical nature of the gas flow through beds, a Snedecor F-distribution was used to describe the gas phase RTD data and hence, the dynamics of the macroscopic flow pattern within the bed was determined from the intensity function, I(t). This indicated initial gas recirculation in stagnant zones within the bed with the flow pattern subsequently evolving into predominantly a channelling and bypassing type. Interestingly, the liquid phase mixing behavior appeared to be independent of Re-G and thus, Pe(L,Raschig) = A(L)Re(LbL) for the unstructured bed, but flow through the more open Bale packing revealed two types of mixing regimes, with a crossover from the region of decreasing Pe(L) to increasing Pe(L) with an increased liquid flow rate at Re-L of about 750 and accordingly, Pe(L,Bale) = A(0) + A(1)Re(L)A(2)Re(L)(2). Liquid hold-up, H-0L, could be decoupled into a static component, H-SL, and dynamic contribution, H-DL, with the latter being proportional to the liquid flow rate. The Bale packing has a higher static hold-up (0.225) than the randomly packed Raschig rings (0.100) due to its more open structure. On the whole, it seemed that liquid phase back-mixing was generally lower in the unstructured packed bed than in the structured Bale packing. The associated higher static hold-up and reduced sensitivity with increasing liquid flow rate makes the latter the preferred choice for catalytic distillation for operations bounded by the loading and flooding envelopes.