We report on a combined TPD and STM study of O2 adsorption and dissociation on various Pt surfaces with varying (111) terrace widths and either (110) or (100) step geometries. Our quantitative TPD results show that (110) stepped surfaces adsorb considerably more oxygen at 100 K, regardless of terrace width, than either (100) stepped surfaces or planar Pt(111). These results suggest that O2 dissociates on the (110) stepped surfaces at 100 K, well lower than required for temperature-induced dissociation on (111) planes. The amount of oxygen desorbing from recombinative desorption of adsorbed oxygen atoms is also greater on (110) stepped surfaces. In addition, the partitioning of adsorbed oxygen between molecular and dissociative states depends on the step geometry; (110) stepped surfaces show an uptake plateau indicative of a threshold surface concentration for low-temperature dissociation, whereas (100) stepped surfaces do not. Scanning tunneling microscope (STM) images for various O coverages and surface deposition temperatures confirm low-temperature dissociation on a (110) stepped surface. The STM images also show that terrace width is not a factor in the lowered dissociation barriers for O2 on (110) stepped surfaces.