Ashal'chinskoe and Mordovo-Karmal'skoe crude oils and their components have been studied by thermal analysis and ESR spectroscopy. Directly from the oils as such, two sets of asphaltene fractions (I and II) have been obtained by the two-step addition of 40-fold excess of a precipitant with varying the oil: precipitant ratio in the first step to be 1 : 5, 1 : 10, and 1 : 20. A comprehensive analysis of the results of studying the oils and asphaltene fractions revealed specific features of aggregation of asphaltenes in different oils.