The efficiency of corrosion inhibitors may be reduced in the presence of corrosion product films. In the present paper the relation between surface wettability, corrosion rate and inhibitor performance was investigated on carbon steel specimens with partly protective ferrous carbonate (FeCO3) films in brine/oil mixtures. Two inhibitor base chemicals and a generic model compound were tested. The corrosion and inhibition tests were performed at 60 °C in 3% NaCl brine under 1 bar CO2. Wettability was studied by contact angle measurements on steel coupons with iron carbonate films. In absence of oil, the inhibitors had no significant effect on the corrosion rate. The presence of oil significantly enhanced the performance of some of the tested inhibitors. The addition of the inhibitors leads to a significant change in wettability of FeCO3 for an originally oil-wet surface. For an initially water-wet surface, the FeCO3 remained hydrophilic when inhibitors were added. It was concluded that the main effect of oil is to modify the structure of the inhibitor film.