The enthalpies of combustion of n-octane and 2,2,3,3-tetramethylbutane were measured by precision oxygen-bomb combustion calorimetry. The following values, based on the mass of carbon dioxide produced, are reported for the standard enthalpy of combustion ΔH o o(298.15 K)/kcal th mol −1 of these compounds in the condensed state: n-octane (1), −(1307.43 ± 0.39); 2,2,3,3-tetramethylbutane (c), −(1302.93 ± 0.26). The difference in the enthalpies of combustion of n-octane and 2,2,3,3-tetramethylbutane, important in the assessment of correlation procedures, was the same as reported in the earlier literature.