Thermochemical data of mineral oil fractions are scarce. Due to the complex structure of natural hydrocarbon mixtures, standard heat and Gibbs free energy of formation depend on the sample. A procedure for predicting these proper ties is presented. Both properties depend on the hydrocarbon type and on its molecular weight. The double-bond equivalent (DBE) and the number of olefinic double bonds are the important characterization parameters of the model. DBE can basically be calculated from molecular weight and elemental composition. Alternatively, boiling point and atomic H/C ratio can be used if the model is applied to mineral oil fractions from which boiling curves can be obtained. A criterion for testing the reliability of the estimated DBE value is available, because DBE is also a function of structural group distribution. The relevance of the DBE concept is shown with regard to hydroprocessing of mineral oil fractions. The model can be applied to total average molecules as well as to an arbitrary number of pseudocomponents and continuous mixtures. The difference between feed and product DBE is equivalent to the amount of hydrogen consumed for hydrogenation of unsaturated hydrocarbons. Further properties of the product can be predicted.