Si oxidized sequentially using and isotopic tracers was studied in detail to investigate the oxidation mechanisms for dry oxidation. Analyses of these samples with SIMS provided detail profiles of the 16O and 18O concentration in the oxide. At 1 atm and 1000°C, we found 18O reacted both at the surface of the oxide as well as at the interface. A subsequent anneal of the 18O oxides revealed that 18O in both regions of the was incorporated in the lattice. Both 18O peaks at the surface and at the interface grew with oxidation time. The same 18O peaks also increased in growth rate with lower initial oxidation time. The growth rates for both peaks increased at higher temperatures. Profiles of the 18O in the oxide revealed a solubility limit for the diffusing oxidant in the oxide at . The same profiles also showed very little oxygen diffusion in the network of the oxide .