A flow-mixing calorimeter has been used to measure the excess molar enthalpy H-m(E) Of (cyclohexane + diethyl ketone)(g) and (benzene + diethyl ketone)(g) at standard atmospheric pressure over the temperature range 373.2 K to 423.2 K. The non-ideality of the cyclohexane and benzene was fitted using the Kihara potential, and that of the diethyl ketone using the Stockmayer potential. Cross-terms were calculated using the equation epsilon(12) = (1 - k(12))(epsilon(11)epsilon(22))(1/2) and to fit the measurements on (cyclohexane + diethyl ketone)(g) the value (1 - k(12)) = 1.13 was needed. This value was used to calculate H-m(E) for (benzene + diethyl ketone)(g), but the experimental values were found to be about 25 J . mol(-1) smaller. The difference between calculated and experimental values was described in terms of a quasichemical model which, for the benzene-diethyl ketone interaction, yielded a value of the equilibrium constant K-12(298.15 K) = 0.347 MPa-1 and an enthalpy of association Delta H-12 = -(19.4 +/- 3) kJ . mol(-1). This value of Delta H-12 is larger than that found for the benzene-dimethyl ketone interaction, Delta H-12 = -(16.4 +/- 2) kJ . mol(-1). These interactions with benzene could be due to quadrupole forces which are stronger for interactions between a polar molecule and benzene than between a polar molecule and cyclohexane. While the dipole moments of dimethyl ketone and diethyl ketone are much the same, diethyl ketone is likely to have a larger quadrupole moment.