A correlation formula to estimate chemical exergies of oil fractions and fuel mixtures from enthalpy of combustion and atomic composition is developed. Heat capacity ofa mixture of 10 hydrocarbons was measured in the range 5–290 K. It was shown that contribution of entropy of mixing to exergy of typical oil fractions is about –0.11% in the approximation of ideal solution, and about –0.18% for a real solution.