The distribution of NMR relaxation times and diffusion coefficients has been employed for modeling the composition of typical crude oils both in bulk and in the reservoir rock. Although the relation of relaxation times and diffusion coefficients with viscosity and molecular size in a typical maltene composition has been established for bulk oils, it is known that the presence of asphaltene affects the relaxation times in a complex way not sufficiently understood so far. In particular, it is expected that the interaction of aromatic or aliphatic maltene molecules, respectively, with asphaltene aggregates leads to a different influence on the relaxation time. In this study, we have applied, for the first time, fluorine containing tracer molecules to natural oils of different asphaltene content and investigated the tracers' relaxation time ratios T-1/T-2 and the magnetic field dependence of longitudinal relaxation times, T-1(omega). This strategy has the advantage of specifically determining the behavior of individual tracer molecules, where molecular weight and aromaticity have been considered as variables. One main finding of this study is the remarkably strong change of T-1/T-2 between perfluorinated alkanes and aromatics in the presence of asphaltenes, whereas this ratio remains nearly constant for asphaltene-free oils. The results are interpreted in terms of selective maltene-asphaltene interaction on the basis of frequency dependent relaxation results. The strong contrast of relaxation times allows for a simplified quantification of either asphaltene concentration or aromaticity of maltenes in natural oils.