This study investigated the effect of a steam-explosion pre-treatment on the anaerobic digestion of the two-phase olive mill solid waste (OMSW) or alperujo. The OMSW was subjected to a steam explosion pre-treatment at 200 degrees C and 1.57 MPa during 5 min. After this pre-treatment a solid fraction (SF) and a liquid fraction (LF) were generated. These two fractions were used to obtain methane through anaerobic digestion with the aim of evaluating the effect of the pre-treatment on the methane yields obtained. Biochemical methane potential (BMP) tests of both untreated OMSW and steam-explosion pre-treated OMSW, i.e. SF and LF, as described above, revealed that the maximum methane yield (589142 mL CH4/g Wadded) was achieved for the LF generated after the pre-treatment. From a kinetic point of view the BMP tests of untreated OMSW and the SF obtained after the pre-treatment showed a first exponential stage followed by a second sigmoidal stage after a lag period. By contrast for the LF, only a single exponential stage was observed. (C) 2016 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.