The transesterification of sal oil with methanol using bentonite nanoclay heterogeneous base catalyst was investigated for biodiesel production. A perfectly mixed batch reactor was used to generate intrinsic kinetic data to determine the reaction mechanism and kinetic constants. The influence of temperature (443-493 K), the initial molar ratio of methanol to sal oil (4-12) and catalyst loading (5-25 g catalyst/100 g oil) was investigated over a broad range of sal oil conversion (i.e., 1-98%). High catalyst loading was used to establish the effect of catalyst loading on sal oil conversion to biodiesel. Five heterogeneous kinetic models, namely, Langmuir-Hinshelwood-Hougen-Watson (LHHW), Eley-Rideal (ER-1), modified Eley-Rideal (ER-2), LHHW-ER and Hattori-Shima-Kabashima (HSK) were applied to determine the best reaction mechanism to describe the experimental data over the entire range of operating conditions. Sal oil conversion based on methanol adsorption on the free basic site of bentonite nanoclay was found to be the most reliable rate determining step using the ER-1 model to fit the experimental data based on statistical analysis and mechanistic consideration under different formulation of transesterification feed mixture. Temperature dependent kinetic constants based on ER-1 model with methanol adsorption were determined. Finally, a parametric sensitivity analysis was carried out to know the most sensitive kinetic constants in the input parameter space. Proposed model maybe helpful in scale-up studies and implementation of the model-based control strategy in the large-scale transesterification of sal oil. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.