Biodiesel is a renewable fuel synthesised from plant, waste or algal oils. Though biodiesel can be used as a replacement for diesel fuel, a number of technical issues, including the reduced oxidative stability, limit the application. This research article compares various analytical techniques which can be used to assess the oxidation of biodiesel and, through comparison, elucidate further the products and mechanism of degradation. Rapeseed methyl ester (RME) was oxidised at both 90 °C and 150 °C, aliquots of both the solution and the volatiles were taken and analysed using UV-VIS spectroscopy, FTIR spectroscopy, GC-MS, 1-H and 13-C NMR experiments. The viscosity and the refractive index of the samples were also recorded. Though NMR and GC-MS offer excellent methods to assess the oxidation both require lengthy sample preparation. In contrast in situ FT-IR requires less sample preparation and as such, would be a useful tool for use as an oxidation sensor.