Experimental measurements of the phase equilibria of (CO 2 +butylbenzene) and (CO 2 +butylcyclohexane) have been made with an analytical apparatus at temperatures of (323.15, 373.15 and 423.15)K at pressures from 2MPa to the mixture critical pressure. These are the first results to be published for (CO 2 +butylcyclohexane), while for (CO 2 +butylbenzene) they are the first at pressures above 6MPa. To model the data, we use the Peng–Robinson equation of state with Wong–Sandler mixing rules incorporating the NRTL equation. The model describes the measured bubble point curves very well at all temperatures, except close to the mixture critical points at high pressures. The dew point curves are described well only at the lowest temperature; otherwise, deviations increase in the approach to the mixture critical point.