Knowledge of lateral mixing is essential to understand heat and momentum transfer parameters in both single-phase liquid and two-phase gas-liquid co-current down flow through packed bed columns. The reactors through which gas and liquid concurrently flow downwards through a bed of catalytic packing are called trickle bed reactors. Experimental data on lateral mixing coefficients from both the heat transfer and radial liquid distribution studies are obtained over a wide range of flow rates of gas (0.01-0.898 kg/m(2) s) and liquid (3.16-71.05 kg/m(2) s) using glass spheres (4.05 and 6.75 mm), ceramic spheres (2.59 mm), and ceramic raschig rings (4 and 6.75 mm) as packing materials covering trickle flow, pulse flow, and dispersed bubble flow regimes. In the present work, an expression for estimation of lateral mixing coefficient (alpha beta)(L) is derived using the data on radial liquid distribution studies. The agreement between the values of (alpha beta)(L) obtained from heat transfer studies and from radial liquid distribution studies using the experimental data shows that there exists an analogy between the heat transfer and radial liquid distribution in packed beds. Since (alpha beta)(L) is an important variable for estimation of various heat and mass transfer parameters, a correlation for (alpha beta)(L) based on present heat transfer study is proposed. The agreement between the (alpha beta)(L) values estimated from the proposed correlation and experimental values is satisfactory with a standard deviation (s.d.) of 0.119. (C) 2007 Published by Elsevier Ltd.