Resúmen del autor: The detailed composition of a low total acid number (TAN) crude oil that causes unusually severe water-oil emulsion problems along the production stream was studied by Fourier transform ion cyclotron resonance mass spectrometry and infrared spectroscopy. Distinct fractions, such as asphaltenes, whole interfacial material, extracts from the interfacial material, etc., were prepared for characterization. The detailed compositional analysis of the interfacial material showed the predominance of asphaltenes together with high amounts of distinctive mono- and diprotic naphthenic acids and sulfur- and oxygen-containing aromatic molecules. In addition, the interface was found to be heterogeneous. A primary group of species that is strongly bonded to the water surface consists of fatty monoprotic acids, fatty, naphthenic, and aromatic diprotic acids, and some alkyl benzene sulfonates. A secondary part of interfacial material consists of various classical asphaltene-related components, such as aromatic sulfur-oxygen-containing species, together with naphthenic and aromatic monoprotic acids. This paper focuses on the analytical part of a larger study of the particular tight water-oil emulsion of this Arabian crude oil. The other two parts of this study address rheological and other physical approaches to investigate this water-oil emulsion.