Iodine values (IVs) of some biodiesel samples were analyzed using both H-1 NMR and a standard iodometric method. H-1 NMR was carried out with and without 1,4-dioxane as an internal standard (IS). The results obtained using H-1 NMR with 1,4-dioxane as an internal standard showed better linear fitting and correlation with the iodometric method than NMR without the IS. The proposed H-1 NMR_IS method allows determination of the IV using smaller samples than the iodometric method. Moreover, the determination can be carried out in less than 15 min, dramatically less than the time needed to carry out the iodometric method. (C) 2010 Elsevier Ltd. All rights reserved.