In this paper, exergy analysis was performed under both complete and partial incomplete combustion conditions for stoichiometric (phi = 1) fuel/air mixture ratios including different mole blends of octane and hydrogen in an internal combustion engine. In exergy analysis, temperature and pressure of exhaust gases was accepted as 500 degrees C and 1 atm respectively, and temperature and pressure of ambient as reference conditions was taken 25 degrees C, 1 atm respectively. 1 kmol fuel that consist different mole blends of octane and hydrogen was taken as total fuel amount. As the mole fuel blends were being prepared, the reduction in the amount of octane as percent in the mixture were completed with % hydrogen as percent, and the total fuel amount for each mixture rates was completed to 100%. From the results, it is observed that the exergetic efficiency is approximately 26% for 1 kmol of fuel containing 100% octane, while approximately 30% for 1 kmol of fuel containing 100% hydrogen. The exergetic efficiency for other hydrogen and octane fuel blends is varied in a parabolic structure between these values for both chemical reactions (complete and partial incomplete combustion).