In this work, the esterification and trans-esterification reactions of waste cooking oil (WCO) with high free fatty acids (FFA) (>= 1% by weight) were investigated. This investigation used a two-step batch process with kinetic based reaction mechanisms and examined potential benefits of combining the conventional Fatty Acid Methyl Ester (FAME) trans-esterification method with microwave technology. Optimization of an acid-catalyzed FAME process to minimize FFA content in the feedstock found that a feed volume ratio of 0.3 L of methanol per liter of WCO, 2% grams of sulfuric acid (H2SO4) per gram of WCO for a reaction time of 200 min at a reaction temperature of 60 degrees C produced a biodiesel yield of 24%. By comparison, optimization of a base-catalyzed FAME process found that a feed volume ratio of 0.3 L methanol per liter WCO oil, 1 g of potassium hydroxide (KOH) per gram of WCO for a reaction time of 60 min at a reaction temperature of 60 degrees C produced a biodiesel yield of 93-98%. When microwave irradiation was included, the reaction time for the acid-catalyzed system was 80 min (compared to 200 min) and 10 min for the base-catalyzed system (compared to 60 min). These preliminary results suggest microwave technology merits further investigation for industrial application to biodiesel production. (C) 2020 Elsevier Ltd. All rights reserved.