The anaerobic digestion of lipid-extracted Nannochloropsis at different substrate to inoculum ratios (SIR), biomass concentrations and after thermal hydrolysis pre-treatments exhibited higher CH4 production rates than its non-extracted counterpart. Thermal pretreatment supported a CH4 productivity enhancement of 40% for the non-extracted Nannochloropsis and 15% for the lipid-extracted Nannochloropsis. The higher initial rates of CH4 production for the extracted microalgae, together with this lower extent of enhancement by thermal hydrolysis, suggested that lipid-extraction constituted itself a pretreatment to increase the biochemical CH4 potential of microalgae. From an energy balance viewpoint, the minimum microalgae concentration necessary to achieve an energy-sufficient thermal hydrolysis process depends directly on the CH4 productivity of the pre-treated microalgae. (C) 2013 Elsevier B.V. All rights reserved.