The naphthenic acids found in petroleum may cause serious corrosion problems for processing equipment. In this study, naphthenic acids were removed by catalytic esterification with methanol to reduce the occurrence of corrosion in refinery equipment and to improve the properties of the oil. The influence of the reaction conditions on the esterification reaction was investigated. SnO-Al2O3 was used as the catalyst for the esterification of naphthenic acid in crude oil with methanol in a fixed-bed catalytic reactor. The experimental results demonstrated that a high reaction temperature and a low space velocity promote esterification. For a continuous fixed-bed reactor, the optimum reaction conditions were determined to be a methanol to oil ratio of 2 wt%, a reaction temperature of 300 degrees C and a space velocity of 2.5 h(-1). The total acid number of the crude oil was reduced from 2.8 mgKOH/g to a value below 0.5 mgKOH/g. Furthermore, esterification can be improved by removing water from the crude oil. (C) 2013 Elsevier Ltd. All rights reserved.