Effect of high porosity fiber bed length on steady-state bed coalescence of diluted oil-in-water emulsion was investigated. Interdependences of bed length, flow mode, bed permeability, and inlet concentration were included in this study. For the steady-state bed coalescers the property usually called minimal bed length should be defined as critical bed length, L-k. The critical bed length has to be identified for each application and for each chosen system. Effect of the above critical bed length value on the steady-state bed coalescence is dominantly determined by bed permeability and influent oil concentration, independent on flow mode. (c) 2007 Elsevier B.V. All rights reserved.