Understanding the reactivity of oxide phases on transition metals (TM) are important to a range of catalytic processes under oxygen-rich conditions. Recently, several oxide phases that form on Pd(111) have been identified and their structure determined through LEED and STM. We report on DFT calculations of adsorption and reactivity of these oxide phases to O2, H2O, and CO and compare the behavior of the oxides to the pure Pd(111) metal surface. Our results indicate that the 2D surface oxide has very distinct reactive behavior from the 3D oxides that form under higher oxygen coverages. Comparisons between DFT results and recent TPD work will also be presented.