The wettability of carbon steel surfaces with aqueous media (distilled water, brines) and hydrocarbon media (crude oils) was studied under CO2 corrosion conditions at 75 and 80°C and 5 bar CO2 with respect to the effect of surface active compounds (inhibitors, demulsifiers) by quasi-insitu and insitu contact angle measurements in a high pressure test cell. Fatty alcohol ethoxylates, quats, amines and imidazolines
influence the hydro-philic/hydrophobic properties of carbonate scales on corroding carbon steel, but inhibiting mechanisms cannot be explained by hydrophobmg effects alone. The method yields easy and quick information on substance effects, specifically in case of insitu measurements in oil-in-water systems. Keywords: Carbon steel, carbon dioxide, corrosion, brines, hydrocarbons, crude oils, inhibitors,
demulsifiers, contact angle measurements, high pressure.