Horizontal packed beds are becoming more common in the process industry, especially in gas separation processes where gas adsorption by particles is desirable. However, horizontal cylindrical packed beds have a much more severe maldistribution of fluid flow compared to the standard vertical cylindrical packed beds. Maldistribution of gas flow, as well as local and corner fluidisation, in packed beds of varying cross-sectional area have been investigated in this paper. The velocity profiles at the bed surface of a two-dimensional linear-converging, as well as a linear-diverging packed bed, with 15degrees and 30degrees wall angles were measured by hot wire anemometry at various superficial air velocities. The measurements indicate that local fluidisation in the converging packed bed is caused by the geometry-induced maldistribution of the air flow, occurring when the air velocity near the wall reaches the minimum fluidisation velocity of the packing particles. Generally, higher superficial air velocity will create a higher degree of flow maldistribution, with the velocity profile showing undulating pattern (but without local fluidisation near the wall for the diverging bed). Pressure measurements within the beds show similar trends, thus providing a qualitative verification of the velocity profile measurements. The variation of measured pressure across the packed bed with superficial air velocity does not conform to the Ergun equation especially at high air velocities due to severe maldistribution of air flow and changing cross-sectional area of the packed bed. Based on the experiments and theoretical analysis, the mechanism of gas maldistribution, as well as the effects of packing height, wall insert angle and superficial air velocity are also discussed in this paper. (C) 2003 Elsevier B.V. All rights reserved.