In this paper, we elaborate on our previous communication of high coverages of oxygen on Rh(111) [J. Chem. Phys. 110, 2757 (1999)]. When dosing with O-2, half of a monolayer of O is adsorbed. Higher coverages can be achieved when exposing the surface to O atoms. As the quantity of adsorbed O increases from a half to a full monolayer, the overlayer structure undergoes several distinct phase changes. At a full monolayer, the (1 x 1)-O structure is stable at surface temperatures less than similar to 400 K. Continued dosing with O atoms results in the rapid migration of O into the bulk. We also report on the chemical reactivity of this densely oxygen-covered surface with CO, H-2, and propene.