Analytical methods for the determination of trace elements in oily and viscous samples are necessary, for example, in the case of crude oil and its heavy fractions, where trace elements indicate specific oil characteristics and the geographic location of the natural deposit. Moreover, the quantification of these elements is relevant for geochemical interpretations concerning thermal maturity, oil-oil correlations and primary and secondary oil migration. Knowledge on trace element characteristics of crude oil is also important in oil refining strategies to prevent contamination of catalysts as well as equipment corrosion, and to minimize environmental pollution. In the case of vegetal oils and fats, the presence of certain elements, even in low concentrations ((mi)g g-1); can speed up oxidative processes and premature rancidity of oils, which may cause pathological effects in the digestive system, including cancer. Spectrometric techniques based on inductively coupled plasma (ICP OES and ICPMS) are extensively used for determination of trace elements in such type of samples due to their sensitivities and multielemental features. In the case of oils and fats, the samples have to be generally decomposed by wet-ashing procedures with mineral acids, prior to the elemental determinations. In this work, new strategies for sample preparation of crude oil, diesel, asphaltenes, edible oils, butter and margarine have been developed, which allow the use of the traditional procedure for sample introduction into the ICP by solution nebulization. In the case of diesel oil, the proposed strategy was the preparation of samples as emulsions with n-propanol. Factorial design studies showed that the important factors for the quantitative determination of refractory metals were the sample amount in the emulsion (up to 25% in weight) and the acidification of the emulsion. Crude oil samples, vegetable oils and fats have been prepared as n-propanol microemulsions. Alternatively, an ultrasound-assisted trace metal extraction procedure was developed. The crude oil emulsions with n-propanol were found to be a good environment to keep the analytes in solution. In the case of the ultrasound-assisted acid extraction for crude oil, a factorial design indicated that the important factors for the determination of trace elements have been the sample heating time, the nitric acid concentration and the ultrasound exposure time. For vegetable oils and fats, the optimization of the npropanol emulsion components provided good stability and homogeneity olive and soy oils (6 % of oil in weight) and for margarine and butter (5 % of oil in weight). For the ultrasound-assisted acid extraction, the optimized conditions for sample preparation also allowed the analysis of the extracts by ICP-MS, which results were compared with the ones obtained by ICP OES. For asphaltene samples, the proposed procedure was the ultrasound- assisted acid extraction in concentrated HNO3 using similar conditions employed for crude oil. The figures of merit for the proposed methods were achieved under optimized experimental and instrumental conditions and validations were performed by analysis of certified reference materials (when available), recovery tests, and by comparison of results obtained using traditional sample preparation procedures for this type of sample. Methods for the determination of Cr, Mo, V and Ti in fuel and diesel oils, for Cd, Co, Cr, Fe, Mn, Mg, Ni, Ti, V and Zn in crude oil and for Fe, Ni and V in asphaltenes have been developed. Cd, Co, Cr, Cu, Mn and Ni in edible oils and fats have been determined using the microemulsification in n-propanol, while Al, Ca, Cd, Cu, Fe, Mg, Mn, Ni, V and Zn have been determined after acid extraction in HNO3. The analyses were carried out by using the external calibration method with internal standardization by Sc (in the case of ICP OES). The ultrasound-assisted acid extraction method for t