A flow-mixing calorimeter has been used to measure the excess molar enthalpyH m E (p o ) of (carbon dioxide + dioxane)(g) and (propane + dioxane)(g) at standard atmospheric pressure (p o ) = 0.101325 MPa over the temperature rangeT= (373.2 to 433.2) K. The measurements on (propane + dioxane) were fitted by using (1 −k 12 ) = 0.85 in the combining ruleϵ 12 = (1 −k 12 )(ϵ 11 ϵ 22 ) 1/2 . This value was used to calculateH m E for (carbon dioxide + dioxane) but the measured values were found to be less positive than predicted. The difference was attributed to quadrupole–quadrupole coupling energy and this was estimated by assuming a quasi-chemical model which, for the carbon dioxide–dioxane interaction, yielded a value of the equilibrium constantK 12 (298.15K) = 0.126MPa −1 and an enthalpy of associationΔH 12 =−(8.4 ± 2)kJ · mol −1 . Second virial cross-coefficients have been derived from the measurements.