Oils with high amount of free fatty acid (FFA) are becoming one of the most promising alternatives to produced biodiesel; due, principally, to it low cost. However, because of the presence of FFA, the conventional basic homogenous catalyst should not be used with the aim to avoid the production of soaps. In this work, different catalysts, such as solid resins, zeolite and enzymes, as well as different alcohols: ethanol anhydrous, ethanol 960, 1-propanol, 2-propanol and butanol, were tested for the direct esterification reaction of pure oleic acid. The influence of several variables, such as alcohol's carbon chain length, the presence of water, which has a negative effect on the final conversion shifting the final conversion to a lower level, and the location of the OH group were studied. The enzymatic catalyst, Lipozyme CALB, turned out to be the best one, achieving a final conversion of 98% after three days reaction. (c) 2008 Elsevier Ltd. All rights reserved.