Biomass-derived pyrolysis oils are rich in carbon and can be used as such or can be processed to produce an oil compatible with crude oils to be used in production of fuel and chemicals in petroleum refineries. However pyrolysis oils can be significantly more corrosive compared to traditional fuels. As-produced pyrolysis oils contain a significant amount of oxygen primarily as component of water carboxylic acids phenols ketones and aldehydes. As a result of these constituents bio oils are generally more acidic with a total acid number (TAN) that can reach levels as high as 100mgKOH/g with the measured pH of bio-oils between 2.3 to 3.5. There is a significant variation in the chemical composition of bio-oils due to the source and procedures used to produce these oils. Extent and mode of corrosion attack also depends on the alloy composition microstructure and environmental parameters. If pyrolysis oils are to be successfully used in an existing or a new process stream it is very important to know its effect on the performance of different alloys used in that equipment. To study this effect six materials aluminum Al 1100 copper (Cu) brass (Cu-Zn) Carbon steel (CS) 516-G70 Austenitic stainless steel (SS) 316L and two duplex stainless steel (DSS) 2205 and 2101 were tested in different pyrolysis oils. Corrosivity of pyrolysis oils depend on its water content carboxylic acids as well as other constituents affecting their TAN.