The binary phase behavior of supercritical CO2 with guaiacol, a model lignin monomer that is a liquid at near-ambient conditions, has been determined. A variable-volume, high-pressure view cell was used to observe both liquid liquid cloud points as well as bubble points along the liquid liquid vapor (LLV) three-phase line for this system. CO2 + guaiacol was found to exhibit Type III phase behavior according to the classification system of Scott and Van Konynenburg, indicating that even at high pressures the mutual solubility of the two components is relatively low. However, the system does exhibit a pressure minimum in the liquid liquid critical curve at 15 degrees C and pressures just under 500 bar. The upper critical end point U for the CO2-rich liquid phase extends to temperatures and pressures 2.1 degrees C and 2.2 bar above the critical point of CO2. (C) 2015 Elsevier B.V. All rights reserved.