A two-stage thermophilic fermentation and mesophilic methanogenic process for biohythane production from palm oil mill effluent (POME) was investigated. The hydrogen and methane potential from POME were 170-200 L H-2 kgCOD(-1) and 210-292 L CH4 kgCOD(-1), respectively. A continuous two-stage process with hydraulic retention time (HRT) of 2 d for hydrogen reactor and 15 d for methane reactor, obtained 34% higher energy yield than single stage methane production. The hydrogen and methane yields from two-stage were 210 L H-2 kgCOD(-1) and 315 L CH4 kgCOD(-1), respectively with total energy yield of 15.34 MJ kgCOD(-1). Mixed hydrogen and methane (biohythane) production rate was 4.4 L biogas L(-1)d(-1) with containing of 51% CH4, 14% H-2 and 35% CO2. Hydrogen reactor was dominated with hydrogen producing bacteria of Thermoanaerobacterium thermosaccharolyticum, while acetoclastic Methanoculleus sp. was the dominant methanogen in methane reactor. Two-stage process for biohythane production could efficiently for energy recovery from POME. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.