The hydrogenation of unsaturated heavy compounds is conventionally carried out in the presence of two fluid phases, because the immiscibility in the binary subsystem 'hydrogen + heavy substrate' cannot be overcome by adding a standard solvent. Using a supercritical or quasicritical solvent allows the hydrogen and the unsaturated heavy substrate to dissolve into a single phase. To select the operating conditions of a supercritical reactor, it is necessary to determine the phase boundaries of the subsystems 'solvent + hydrogen' and 'solvent + heavy compound'. In this work, we measured cloud points for binary systems made of polybutadiene (PB) or polyethylene (PE) and a light solvent, i.e., propane or dimethyl ether (DME) or diethyl ether (DEE). The temperature range studied was from 50 to 160 degrees C for 'PB + DME' and 'PB + Propane' and from 100 to 190 degrees C for 'PB + DEE' and 'PE + DEE'. We found that in PB-containing binary systems, at the ranges of conditions of the experiments, the minimum pressure required to guarantee homogeneity, at any temperature, is below 200 bar for DEE, below 300 bar for DME and in the order of 500 bar when using propane as solvent. Our data for 'PE + DEE' indicate the need for a minimum pressure of about 240 bar to keep the system within a single phase. The results from this work and from the literature suggest that the use of binary solvent mixtures may be convenient to carry out the supercritical hydrogenation of PB. (C) 2010 Elsevier B.V. All rights reserved.