This thesis investigates the acetylation of the unsaturated groups present in the hydrocarbon chain of rapeseed oil and esterification of the hydroxyl groups present in hydrogenated castor oil. The reaction of carboxylic acids, acetic anhydride and acid chlorides with the hydroxyl group of solid hydrogenated castor oil is explored to instigate a change in the physical properties. Such modifications often change the solid, lard-like material, into a liquid with potential for use as a dielectric fluid. The reaction of hydrogenated castor oil with acetic acid and sulphuric acid or PTSA as catalysts, results in 98% yield for esterification of the hydroxyl group after only 2 hours reaction at 120 °C. At this point, there is evidence that unsaturation in the chains of the ricinoleic acid starts to appear.