PURPOSE: To remove organic acids and inorganic salts and prevent a purifier from corrosion, by bringing an oil with a high total acid value into contact with a mixture solution of an organic amine or ammonia, alcohol and water.

CONSTITUTION: An oil with a high total acid value of ≥0.5mg-KOH/g is brought into contact with a mixture consisting of (A) preferably an organic amine, such as dimethylamine or monoethanolamine, or ammonia, (B) about 5W40vol.% alcohol and (C) about 2W6vol.% water. The resultant mixture is then separated into phases of an oily phase, alcohol-aqueous phase and the organic amine and alcohol are subsequently recovered from the above-mentioned alcohol- aqueous phase for reuse.