It has been known that hydrocarbons (oil or gas condensates) protect steel from corrosion, containing natural surface-active species that might form a persistent hydrocarbon film adhering to the steel surface. However, the role of hydrocarbon in sweet corrosion has been confused because of the difficulty in lab simulation. Only sketchy information on the role of hydrocarbon on sweet corrosion has been published. Our recent laboratory results employing the rotating cylinder electrode (RCE) demonstrated that hydrocarbon accelerated localized corrosion at the brine-hydrocarbon interface when hydrocarbon and brine are separated but concurrently moving. Hydrocarbon appears to destabilize the formation of a passive iron carbonate film, accelerating the “localized” corrosion. The corrosion rate (penetration) at the interface exceeded others reported in brine only under similar test conditions. This finding contradicts the conventional view. Our approach appears to make it quantifiable to simulate the role of hydrocarbon observed at top-of-line (TOP) sweet corrosion of gas condensate pipeline.