The heat of mixing (Delta H-M) of the carbon dioxide + tert-butyl methyl ether system was measured near the critical point of carbon dioxide using a flow-type isothermal microcalorimeter at 298.15 and 303.15 K and 5.0-7.0 MPa. The mixtures showed strong exothermic behavior in these regions. The maximum absolute value of Delta H-M (maximum exothermic value) was about 7.9 kJ mol(-1) at 298.15 K and 5.0 MPa. A two-phase region, where Delta H-M varied linearly with composition, was found in the CO2 rich region at all temperatures and pressures except at 298.15 K and 7.0 MPa. (C) 2016 Elsevier B.V. All rights reserved.