Using scanning tunneling microscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy. we studied the evolution of the structure and chemical state of a Rh(110) surface, modified by K adlayers and exposed to high O-2 doses at elevated temperatures, We find that oxygen coadsorption on the K-covered Rh(110) leads to massive reconstruction of the Rh(110) surface. Stable reconstructed (10 x 2) and (8 x 2) segmented phases with a local coverage of more than two oxygen atoms per surface Rh atom were observed. Formation of surface oxide, which coexists with the (10 x 2) and (8 x 2) segmented adsorption phases, is evidenced at the highest O-2 doses. The development of strongly reconstructed adsorption phases with oxide-like stoichiometry and surface oxide under UHV conditions is explained in terms of the stabilization of the (1 x 2) reconstruction and promotion of O-2 dissociation by the K adatoms.