The effect of thermal pretreatment on two-phase olive mill solid waste was evaluated by chemical oxygen demand solubilisation and biochemical methane potential (BMP) tests. Temperatures of 100, 120, 160 and 180 degrees C were applied during 60, 120 and 180 min for each temperature studied. The highest chemical oxygen demand solubilisation after pretreatment (42%) was found for 120 and 180 degrees C during 180 min in both cases. These two conditions were selected for the BMP tests. BMP tests showed two different stages: a first exponential stage and a sigmoidal zone after a lag period. No influence of the pretreatment was observed on the kinetic constant of the first-stage. Clear difference was observed in the maximum methane production rate of the second stage, 76.8 mL CH4/(g VS day) was achieved after pretreatment at 180 degrees C (180 min), value 22% and 40% higher than that obtained for the untreated and pretreated OMSW at 120 degrees C, respectively. (c) 2013 Elsevier Ltd. All rights reserved.