Biodiesel production by in situ esterification/transesterification of Botryococcus braunii microalgae biomass was studied in this work. The effect of different experimental parameters including moisture content, catalyst dosage and methanol to co-solvent ratio (v/v) were evaluated in the proposed reaction process. The selected experimental parameters were found to be significant for the in situ reaction process. A theoretical maximum fatty acid methyl esters (FAME) yield of 80.1% was reached using microalgal biomass with a 28.5% moisture content, a catalyst dosage of 148.7 wt%. with respect to total fatty acid content and a methanol:petroleum ether ratio 2.9:1 v/v. The obtained results show that the reaction took place using wet biomass with moisture content up to 30%, due to the high solvent content provoking water dilution in the reaction medium. For reaction kinetics modelling, the experimental data were fit to a simultaneous esterification and transesterification model. The esterification model was used due to the high free fatty acids (FFA) content and suitably represented the experimental data; however transesterification reaction also took place. Thus, a model considering simultaneous esterification and transesterification on overall FAME production rate was proposed. (C) 2015 Elsevier Ltd. All rights reserved.