Metal oxidation processes are extensively used in technology for protection of materials against corrosion, and production of engineering ceramics and catalysts. The initial stages of oxidation (including oxygen adsorption and incorporation, oxide islands nucleation, and growth into a continuous film) have been actively studied and are now understood relatively well. The kinetics of thick (>200 Å) oxide films approximately follows the parabolic law. It can be described, at least qualitatively, by the Wagner model of oxidation, in which diffusion across the oxide film is the rate limiting process. The situation is much more complicated in the case of very thin (<100 Å) films. The kinetic equations in this region can not be integrated exactly, and only approximations for the oxide growth rate as a function of time can be obtained. This makes the experimental verification of theory based only on the measurements of the oxidation kinetics difficult. However, the use of tracer atoms (both metal and oxygen) provides valuable information on the transport mechanism (e.g. migrating species) in the oxidation process, and can be useful tool for the experimental test of theory. The tracing of oxygen species is usually performed by oxidation first in ¹⁶O₂ and then ¹⁸O₂ enriched gas. Thin (~10 - 20 Å) oxide film growth on Al(110) at moderate temperatures (from room temperature to several hundred degrees Celsius) is being studied utilizing oxygen isotope labeling combined with high-resolution MEIS.