The distribution and the degree of correlation of 14 main and most easily measured characteristics of the structural-group composition of Western Siberia crude oils have been studied. It has been shown that the distribution pattern of the parameters greatly differs from the normal distribution and substantially varies, with the distributions of the quantities that reflect the concentration and composition of aromatic components being the most complex. The trends of variation in composition of the oils in basic stratigraphic plays have been revealed. The necessity of calculating Spearman's instead of Pearson's pair correlation coefficients for determining the degree of interrelation between the parameters has been shown. It has been demonstrated that the conclusions made earlier on the basis of Pearson's linear correlation coefficients about interrelations between the composition parameters and their correlation with the mode of occurrence are not quite certain; all of them need to be verified. Strong interrelation of many composition parameters has been proved, and the necessity of studying in detail the feasibility of their joint use for comparative analysis of oil samples has been suggested. A strong negative correlation between the parameters reflecting the concentration of the aromatic and n-alkyl components has been revealed.