The calculation of the chemical exergy is a very important part of the exergetical analysis. Many scientists, such as Z. Rant, D. Buimovici, W. Fratzscher, H. Baehr and E. Schimidt, attempted to determine chemical exergy of fuel with different methods. In this paper is presented the calculation of chemical exergy of fuel based on the J. Szargut and T. Styryiska method which have developed the Z Rant method.Some numerical examples of calculation are presented at the end of the papers.