In the present study, a scientific challenge of determination of various structural parameters of asphaltenes of medium heavy, heavy, and light crude oils is overcome by different spectroscopy techniques. Fourier Transform Infrared spectroscopy methods revealed indexing information besides clarification of different functional groups of asphaltenes. Analysis of Raman spectra of asphaltenes exhibited a higher average molecular size and more complicated chemical structures for the light crude oil asphaltenes compared to the ones from the heavy and medium heavy oils. Clarification of such chemical structures reveals why asphaltene molecules form aggregates leading to precipitation in particular when the percentage of asphaltenes is closer to and less than 1 wt % as in the case of light crude oils.