The passive film on Fe-Cr binary alloys has been modeled using a network in which Cr+3 ions occupy sites on a honeycomb lattice and O-2 ions form a Kagome lattice. Percolation theory is used to determine the critical composition of the oxide film where -Cr+3-O-2-Cr+3- bonds percolate across the oxide film. The calculated result of 0.34 cation fraction Cr+3 in the oxide film is in excellent agreement with the result obtained previously using graph theory. (C) 2008 The Electrochemical Society.