The organic acids present in petroleum, commonly called "naphthenic acids" (NA), are identified as carboxylic acids of the general formula "RCOOH", where R represents a hydrocarbon chain that does not necessarily show cycloaliphatic structure. The presence of stable oil-in-water emulsions in the crude oils hinders the dehydration process, which is required during the production step. Some compounds, such as the organic acids (NA) present in the crude oils, are involved in the stabilization of the emulsions, because of their amphiphilic structure. The emulsion-breaking process is improved if the organic acids are determined qualitatively and quantitatively. We proposed the study of a quantitative extraction procedure of NA contained in crude oils. First of all, we performed the liquid-liquid extraction of the organic acids, using alcoholic solutions. Because this method did not allow the quantitative recovery of the acids, we developed a separation process based on an ion-exchange resin (QAE Sephadex A(25)). The isolated acid fraction was then derivatized as methyl esters and quantified by gas chromatography experiments, using the internal standard method allowing the determination of the NA composition. The extraction yield was checked via the total acid number (TAN) measurement, using the standard ASTM D664-95 (IP 177/96), which is the standard method commonly used in the oil industry. The extraction of NA on ion-exchange resins required the preliminary study of a model molecule mixture of carboxylic acids, to ensure the complete control of the procedure. Four crude oil samples that were provided by Total (France) (Y1, Y2, Y3, Y4) were then analyzed. The results confirmed the presence of such acids in the crude oils.