This article reports the results of an experimental study on explosion pressure measurement in closed vessel deflagration for methane-air mixtures over its entire flammable range at standard pressure and temperature in vessels with variable geometry and size- 20-L spherical, 27-L cubical, 0.8 m(3) rectangular and 25.6 m(3) spherical-under quiescent conditions using electric spark (3 J) as ignition source. The outcome of the study is comprehensive data that quantify the dependency of explosion severity parameters on gas concentration and vessel volume. The information is required to quantify the potential severity of an explosion, design the vessels able to withstand an explosion and to design explosion safety measures for installations handling this gas. The data presented include maximum explosion pressure, explosion time and rate of explosion pressure rise in terms of deflagration index over a range of methane-air equivalence ratio (phi: 0.53-1.52). The maximum explosion pressures are: 8.6, 8.4, 8.2 and 8.0 bar in 20-L sphere, 27-L cubical vessel, 0.8 m(3) rectangular vessel and 25.6 m(3) sphere, respectively, at phi=1.05. Time to reach the maximum explosion pressure varies from 80 ms in 20-L sphere to 680 ms in 25.6 m(3) sphere. The deflagration index values are: 82, 84, 86 and 106 bar m/s in 20-L sphere, 27-L cubical vessel, 0.8 m(3) rectangular vessel and 25.6 m(3) sphere, respectively, at phi=1.05. The deflagration index increases with increase in size of the test vessel. (C) 2017 Elsevier Ltd. All rights reserved.