Biodiesel has emerged as a promising renewable and clean energy alternative to petrodiesel. While biodiesel has traditionally been prepared through homogeneous basic catalysis, heterogeneous acid catalysis has been investigated recently due to its ability to convert cheaper but high free fatty acid content oils such as waste vegetable oil while decreasing production cost. In this work, the esterification of free fatty acid over sulfated zirconia and activated acidic alumina in a batch reactor was considered. The models of the reaction over the catalysts were developed in two parts. First, a kinetic study was performed using a deterministic model to develop a suitable kinetic expression; the related parameters were subsequently estimated by numerical techniques. Second, a stochastic model was developed to further confirm the nature of the reaction at the molecular level. The esterification of palmitic acid obeyed the Eley-Rideal mechanism in which palmitic acid and methanol are adsorbed on the surface for SO?/ZrO?-550°C and AcAl?O? respectively. The coefficients of determination of the deterministic model were 0.98, 0.99 and 0.99 for SO?/ZrO?-550°C at 40, 60 and 80°C respectively and 0.99, 0.98 and 0.96 for AcAl?O? at the same temperature. The deterministic and stochastic models were in good agreement. / Master of Science