Equations to describe the relationships between 37 pairs of fairly well correlated basic and most easily NMR-measurable characteristics of the structural-group composition of Western Siberia crude oils have been derived. Different variants of graphing the regression lines have been considered. A method for processing initial data has been proposed that suits the standard situation for petroleum geochemistry when the scatter of data points around the trend line is determined by differences between the samples, rather than measurement errors. The characteristics of the deviations of values for the composition parameters from their trend lines, by which a reasonable sequence of the extension of the sets of measured parameters can be built in a comparative study of the composition according to the research objectives, are reported. It has been demonstrated that the given description of the composition can help to identify objects that stand out and are unique in this sense and provides new criteria for grouping fluids of this kind. It has been shown that the parameter C-ar defining aromaticity of the samples from Western Siberia can be calculated with good accuracy from the value of the rapidly and inexpensively measurable quantity H-ar. A correlation between the aromaticity of the samples and the amount of n-alkyl structures in them has been revealed.