The carboxylation of glycerol to glycerol carbonate in the presence of rhodium complexes with phosphine ligands has been studied. It has been found that rhodium complexes are active in the presence of a quaternary or inorganic salt and mediate this reaction with 100% selectivity. The most effective catalyst has been obtained by promoting the {RhCl3 + PPh3} system with potassium iodide. The reaction has been run in a reducing environment in a methanol solution at a temperature of 140 degrees C and a pressure of 50 atm (40 atm of CO2 and 10 atm of H-2).