The search for jet fuels with high energy intensity and physical density is an urgent task in connection with the increased scope of use of unmanned aerial vehicles. This study presents the results of an investigation on the influence of various factors on the molar and mass enthalpies of combustion and molar volume of C_nH_m hydrocarbons of various structures. The findings can become necessary to substantiate the algorithm for searching for energy-intensive hydrocarbons. Additive group-contributions that allow predicting with sufficient accuracy the molar standard (gross) heat of combustion and the molar volume of hydrocarbons in the condensed state were proposed. It was found that the decisive factor for achieving high values of the molar-energy content of hydrocarbons is the m/n ratio and not the number of small carbon cycles in the molecule. Sometimes the presence of a large number of cycles can even lead to a decrease in the enthalpy of combustion. The proposed additive group-contributions can be used to predict the values of molar enthalpies of combustion and molar volumes of fuels with known composition and select the fuel composition according to the required value of molar or volume enthalpy of combustion.