There has been recent interest in expanding the fundamental understanding of catalytic behavior in oxygen-rich conditions on transition metal surfaces. Dramatic improvements in fuel efficiency could be realized if we could operate internal combustion engines in fuel-lean, oxygen-rich conditions, but this would require new catalysts capable of handling the NOx emissions. Transition metal surfaces, when placed in oxygen-rich environments, form surface (2d) and particle (3d) oxides that often exhibit dramatically different reactivity than clean metal surfaces. There is still very little understanding of the transition from chemisorbed surface oxygen phase at low O coverages to the observed oxide phases at higher coverages. We have performed Density functional theory (DFT) calculations of the oxidation of Pt(111) and Pd(111) surfaces. We have examined the thermodynamic stability and kinetics of subsurface oxygen as a function of surface O coverage for both Pt(111) and Pd(111). While the subsurface O becomes more stable than surface chemisorbed O at coverages around 3/4 ML, the energy barriers for O to diffuse into the subsurface are very large (> 2 eV). We will report on our efforts to examine alternative mechanisms for O incorporation into the subsurface. Our initial results will serve as a base for future DFT calculations that will examine more complex mechanisms of oxide formation on transition metal surfaces.