A kinetic model of the physicochemical processes occurring during the corrosion of steel covered by a thin water film exposed to a CO2 atmosphere is proposed. This model explains theoretically the unusual physicochemical behaviors generally observed in such confined corrosive media: Fe(II) supersaturations, low corrosion rates, high pH values, and their respective dependence on the electrolyte film thickness. More quantitatively, the model predictions agree well with pH and corrosion rate measurements performed in environments similar to the annulus space of flexible pipelines. (c) 2007 The Electrochemical Society.