The term biodiesel refers to the Fatty Acid Alkyl Esters (FAAE) derived from vegetable, animal or waste oil feedstocks. This alternative fuel is increasingly becoming a significant part of the transport sector with over 10 million tonnes sold in the EU in 2007. Currently a small amount of biodiesel (presently 3.5% in the UK) is present in diesel fuel but this could rise to up to 30% in the medium term. As biodiesel is not one chemical compound but an amalgamation of different FAAE, the physical properties of the diesel fuel are not only dependent on the amount of biodiesel in the diesel fuel (blend level) but also on the fatty acid pro. le of the biodiesel. In this paper we report on an initial study to assess a range of current techniques which could be used in the future as a basis to determine blend level in unknown samples of diesel and gain further information on the fatty acid pro. le of the biodiesel in the blend. The three techniques applied were FT-IR spectroscopy, refractive index and UV-Vis spectroscopy. (c) 2009 Elsevier Ltd. All rights reserved.