The resonance (delocalisation) energy of benzene is approximately 150 kJ/mol (about 36 kcal/mol). This is experimentally determined by comparing the actual heat of hydrogenation of benzene (~208 kJ/mol) with the theoretical value calculated for a hypothetical cyclohexatriene (~360 kJ/mol). The difference (~150 kJ/mol) represents the extra stability due to aromatic delocalisation.