This study focuses on the thermal reaction between glycerol and ethylene carbonate to obtain glycerol carbonate and ethylene glycol under solventless homogeneous operation, the process being a transcarbonation of glycerol or a glycerolysis of ethylene carbonate. As the two reagents constitute an immiscible system at 40 °C evolving into a single phase at 80 °C, the evolution of phases with temperature was studied by focused beam reflectance measurement. As the biphasic system was inert, runs were completed under a monophasic regime from 100 to 140 °C with molar ratios of ethylene carbonate to glycerol of 2 and 3, achieving quantitative conversion of glycerol, as corroborated by a thermodynamic study. Second order potential kinetic models were proposed and fitted to the data. Finally, a comparison with analogous catalytic approaches was made, showing that this process performs better material-wise.