Gas-water relative permeability behaviour of seven European coals of different ranks was characterised in order to enhance the scientific understanding of the fundamental processes of two-phase flow taking place within the macrostructure of coal. Laboratory experiments were carried out on cylindrical coal samples using the unsteady state method to measure gas-water relative permeabilities due to its operational simplicity. The impact of factors such as wettability and overburden pressure on coal relative permeabilities were assessed. Considerable variation in the shapes of the relative permeability curves for different rank coals was observed, which was attributed to the heterogeneous nature of coal. (C) 2014 Elsevier Ltd. All rights reserved.