In this work, fatty acid methyl esters (FAME), as biodiesel components, were continuously produced via the heterogeneously catalyzed transesterification of palm oil with methanol vapor in a countercurrentflow trickle-bed reactor. Dolomitic rock was used as natural calcium source in the preparation of the calcium oxide-based extrudate catalyst via a physical mixing method. Effects of operating parameters on the FAME yield and the two-phase flow behavior were investigated. The reaction system was characterized by a high mass diffusion resistance at gas-liquid-solid interfaces due to the low solubility of methanol in triglycerides and the high viscosity of oil. Mixing palm oil with commercial grade methyl decanoate, a C10 methyl ester (C10 CME), at a 1:1 mass ratio during the start-up period promoted FAME production. The FAME yield was enhanced by increasing the operating temperature and the methanol flow rate, while operation at a high oil flow rate severely decreased the FAME yield. The concentration of C10 CME, which acted as an emulsifier, in the catalyst bed was crucial to maintain the FAME production stability. In addition to a high FAME yield (ca. 92.3 wt%), the system provided glycerol, obtained without any washing, at a high purity of 93.6 wt%. (C) 2020 Elsevier Ltd. All rights reserved.