Batch hydrogenolysis of concentrated glycerol has been conducted over different Cu/ZnO-based catalysts prepared by the coprecipitation method. The catalysts were characterized by X-ray diffraction, H-2 temperature-programmed reduction, and the N2O titration technique of measurement of the metallic Cu surface area. Results show that the reaction system is affected by hydrogen pressure, temperature, glycerol concentration, and the surface area of metallic copper. Our results tend to show that the reaction scheme is more complicated than the commonly accepted dehydrationhydrogenation mechanism. Tests conducted with varying hydrogen pressure indicate that the mechanism may begin with the dehydrogenation of glycerol to glyceraldehyde. Tests conducted with varying water content tend to show that high water content favors ethylene glycol (EG) formation. The selectivity to 1,2-propanediol (12PG) versus ethylene glycol is a function of the relative reaction rates where the glyceraldehyde can react to either yield 12PG or go through a retro-Claisen route to yield EG. Finally, multiple catalytic tests conducted with a constant amount of copper surface area show that, according to the MadonBoudart criterion, the catalytic system is heavily hampered by transport phenomena limitations.