Oxygen adsorption on the Rh(100) surface has been studied by spot profile analysis low energy electron diffraction (SPA-LEED) and scanning tunnelling microscopy (STM). Our results show that oxygen can be reliably dosed onto the Rh(100) surface to produce distinct p(2 2) and c(2 2) phases. Additionally, the symmetry of the phase formed at saturation coverage is identified as (2 2)p4g rather than (2 2)p2gg as had been proposed previously. STM images of both the c(2 2) and (2 2)p4g phases show that the O atoms sit in alternate four-fold hollow sites. It is proposed that the difference between these two structures is a result of overall oxygen coverage. In the c(2 2) case we speculate that surface strain is relieved by the formation of islands, but that for the saturation coverage (2 2)p4g structure surface strain is reduced by the O atom burrowing into the surface, causing the characteristic clock reconstruction of the substrate Ph atoms.