Based on an approach to finding structure-property relationships, we constructed models for calculating the octane and cetane numbers of individual hydrocarbons (alkanes and cycloalkanes). The models obtained for octane numbers are superior to well-known analogous models described in the literature in terms of the accuracy and predictive efficiency. This is the first attempt to develop a model of this kind for the cetane number. The results of the calculations of these characteristics for a number of unsynthesized and uncharacterized compounds are given.