Parametric-effects On kinetics for biodiesel production from H2SO4-catalyzed esterification of free fatty acids (FFA) with methanol are evaluated at different intervals of reaction using Taguchi method. The parameters studied with orthogonal array design are catalyst loading, temperature, and methanol-to-FFA mole ratio (MR). Within the range of the parameters studied, each parameter has positive effect on conversion of FFA (X-FFA) throughout the reaction wherein trans-esterification of oil is found negligible. But relative-contribution of temperature to X-FFA declined similar to 23.5% (from 55.77% at 10 min to 32.39% at 180 min) and that of MR increased similar to 29%. (from 21.46% at 10 min to 50.45% at 180 min). Catalyst loading has minimal effect on X-FFA throughout the reaction (contribution varied within 15-24%) and has constant effect on FFA-esterification rate beyond 75 min. The relative effect of reaction time (as an independent parameter) along with other parameters is also evaluated at different reaction-phases and the orders of parametric-effects are compared with the results of the detailed analyses (using Taguchi approach) of esterification-kinetics data of published works for biodiesel synthesis. The relative parametric-effects on kinetics are found to be a I-Unction of reaction duration; parametric-order changes as reaction progresses toward equilibrium. However, temperature and MR are the more dominant parameters than catalyst loading and reaction time. Taguchi additivity model is validated with experiments and the predictions deviated within +/- 5%. (C) 2013 Elsevier Ltd. All rights reserved,