Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Biodiesel produced mainly by the base-catalyzed transesterification of vegetable oils or animal fats with a short chain alcohol, has become an attractive alternative to petroleum-based diesel fuel. Even though high-field H-1 nuclear magnetic resonance (NMR) is a reliable method for biodiesel quality control, it is restricted by its poor mobility and expensive superconducting coils. As an alternative, this study presents a mobile low-field H-1 NMR spectrometer for the analysis of biodiesel samples derived from different feedstock oils. The low-field H-1 NMR spectra of all the compounds coexisting in a typical transesterification reaction such as rapeseed oil, rapeseed biodiesel, methanol, and glycerol, could be clearly differentiated. Field-dependent characteristic parameters such as relaxation times are provided. The degree of saturation of the different biofuels samples could be reliably estimated via integration of the resolved signals of the spectra. The obtained results agreed well with those measured at high-field H-1 NMR. Since this compositional information is directly related to the biodiesel properties, the presented mobile low-field H-1 NMR device built from permanent magnets arrayed in a Halbach geometry, constitutes an excellent alternative tool for biodiesel quality control.44416714153Deutsche Forschungsgemeinschaft (DFG)Deutscher Akademischer Austausch Dienst (DAAD)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)