An epoxidation reaction of different types of feedstock, depending on the iodine values, through percarbonic acid route generally generated different amount of heat. Thus, the heating and cooling temperature of the system and reaction need to be regulated to accommodate production of epoxidised products with oxirane oxygen content (OOC) value nearest to the targeted OOC. Four in situ epoxidation reactions, namely Entry 1-4, utilising formic acid and concentrated hydrogen peroxide, were conducted with continuous control of heating and cooling with real time temperature monitoring. All the reactions gave OOC values of between 3.17%-3.37% determined at the 240th min of the epoxidation process. These values were consistent with the theoretical OOC of 3.41% of refined, bleached and deodorised (RBD) palm olein. The neutralisation, washing and drying processes did not alter the OOC values of all the epoxidised products (EPO) giving final dry EPO of OOC between 3.19%-3.32%. The study revealed that epoxidation reaction of RBD palm olein has to be conducted at temperatures within 30°C to 60°C by suppressing the heat generated from the reaction through efficient heating and cooling system.