The experiments were carried out in excess ethylene glycol (EG) and poly(ethylene terephthalate) (PET) oligomer in the presence of zinc acetate as catalyst at 190 degrees C. It was found that during the glycolysis reaction, the monomer and dimer were contained in the liquid phase. After 2 h of the glycolysis reaction, an equilibrium state between the monomer and dimer was seen to approach. The equilibrium value of 0.51 between the monomer and dimer obtained at 190 degrees C was in good agreement with previously published values. It was found that the catalyst concentration facilitated equilibrium and increased the glycolysis rate. A reduced amount of EG in the initial feed resulted in a decrease in the glycolysis rate.