The main material for product tank production is carbon steel, which is generally resistant to corrosion in crude oil, but prone when it comes in contact with water contained in basic sediment or hydrostatic testing media. The corrosion shortens the life of the tank and can cause leaks which pose a danger to public health and safety and to the environment. Special attention should be addressed to bare surfaces of the tanks when mild steel is in direct contact with water, such as during hydrostatic testing. This paper examines the usage of corrosion inhibiting oil as a float coat for short-term general corrosion mitigation of carbon steel tanks during the hydrostatic testing with sea water. The corrosion inhibiting oil floats on the surface of the water and forms a protective layer in contact with internal tank walls thus preventing the direct contact of sea water with bare tank surfaces. The anticorrosion properties were evaluated by means of electrochemical polarization testing. The carbon steel samples were protected by corrosion-inhibiting oil and exposed to pure sea water, sea water inhibited by oxygen scavenger, and sea water inhibited by oxygen scavenger and treated with biocide, which are all possible hydrostatic testing media. The tested corrosion-inhibiting oil showed significant mitigation properties of general corrosion of the carbon steel samples.