Reactive vacuum vapor deposition of aluminum oxide thin films by an air-to-air metallizer was examined via the direct simulation Monte Carlo method and experiments. Comparison of the calculated results with the measurements of the Al oxide thin film's thickness showed (a) that the empirical flux of Al atoms arriving at the substrate is lower than the calculated result, probably due to the formation of Al oxide on the evaporation surface and (b) that the amount of oxygen calculated from the thickness of the film is twice the amount corresponding to the calculated flux, probably due to the effects of the decreased sticking coefficient of oxygen on the evaporating surface and sidewall, underestimated gas phase reaction, large mesh size overestimated film density, and formation of substoichiometric oxide. Aluminum oxide thin films deposited on plastic film substrates by this metallizer under strictly controlled O-2 supply conditions have good transparency, an oxygen transmission rate of 2.7 cc/m(2) day, and an electrical resistivity of 4.4 X 10(6) Omega(2) m. Furthermore it was found that the oxygen transmission rate was reduced greatly to 1.0 cc/m(2) day or less when the Al oxide coating film was laminated with another plastic film using an adhesive. (c) 2006 American Vacuum Society.