In this work the phase behavior of a binary mixture consisting of a supercritical fluid and an imidazolium-based ionic liquid (IL) was studied experimentally. Carbon dioxide was selected as the supercritical fluid and 1-ethyl-3-methytimidazolium hexafluorophosphate was considered as the IL. A synthetic method was used to measure vapor-liquid boundaries. Results are reported for carbon dioxide concentrations ranging from 10.4 up to 61.9 mol%, and within temperature and pressure ranges of 308.14-366.03 K and 1.49-97. 10 MPa, respectively. Also, the experimental results obtained in this work were compared with other available binary systems of supercritical fluid + IL. (C) 2003 Elsevier B.V. All rights reserved.