The experimental procedure using Amberlyst® 15 as heterogeneous catalysts only differs slightly from the procedure using sulphuric acid. In the experiments with Amberlyst® 15, oleic acid and ethanol are mixed in the reactor and heated up,because the non-catalytic reaction is considered to be negligible. After reaching the reaction temperature a sample is taken to verify the assumption that the acid index in the mixture at room temperature do not change after reaching the reaction temperature. To start the reaction the heterogeneous catalyst was added and this point was defined at time 0. Samples are taken over the whole reaction time to observe the progress of the reaction.