The interaction of oxygen with Al(111) was investigated by STM at temperatures between 350 and 530 K, by annealing an oxygen precovered surface and by adsorption of oxygen on the hot surface. For exposures up to 10 L and temperatures up to 470 K a considerable part of the oxygen exists still in the chemisorbed state, another part transforms into Al oxide. In contrast to 300 K chemisorbed O-ad atoms are mobile at elevated temperatures, and compact, hexagonal (1 X 1)O-ad islands develop by an ordinary nucleation and growth scheme, This evidences attractive interactions between the oxygen atoms on (1 X 1) sites, From the lateral distribution of O-ad islands a diffusion barrier of 1.0-1.1 eV is derived, The imaging of the islands of the (1 X 1) phase by STM depends on their size, which is understood by a different imaging of the O-ad/Al adsorbate complexes at the island borders. Defects in the islands and bright features at the edges are interpreted as nuclei of aluminum oxide. Additional features which appear as topographic holes may be attributed to nonconducting Al oxide grains.