Gamma ray tomography experiments have been carried out to detect any spatial patterns in the porosity in a 0.6 m diameter packed column. Three different sizes of stainless steel Pall rings (16, 25 and 38 mm) have been examined. The primary objective is to detect spatial patterns and statistical information on porosity variation in packed distillation columns. Such data are needed in the computational fluid dynamics simulators based on volume averaged equations. Horizontal scans, at different vertical positions of the packed bed, were made for each size of Pall rings. A tomographic reconstruction algorithm has been used to calculate the spatial variation over the column cross section. Radial porosity variation within the packed bed has been determined. The variation of the circumferentially averaged porosity in the radial direction indicates that the porosity in the column wall region is a somewhat higher than that in the bulk region, due to the effect of the column wall. The probability density function for porosity variation has been constructed from the experimental data and it can be represented by a normal distribution.