Large-scale production of transportation fuels and commodity chemicals through thermochemical conversion of biomass will require a better understanding of the appropriate materials of construction. Processes such as pyrolysis, solvent liquefaction, and hydrothermal processing produce oxygenated bio-oils that can damage materials commonly found in fuel and chemical production facilities. Recent investigations have examined the corrosive effects of these bio-oils on various kinds of steel, but very little effort has been given to determining their effect on polymers used for valve seats and standard gaskets. This project evaluated the performance of several common polymers used in process control equipment after exposure to a simulated thermochemical environment for 48 h. The performance of each polymer was determined by changes in its mass and cross-sectional area. An additional performance metric was the change in polymer hardness, as measured on the Shore durometer scale. All of the polymers tested exhibited an increase in cross-sectional area and mass after exposure to bio-oil, with a decrease in hardness. An increasing temperature tended to exacerbate these effects. Bio-oils with a low molecular weight and a high degree of polarity were found to be the most detrimental. From this, it was concluded that the polarity of both the polymer and bio-oil contributed most significantly to the observed effects. Nitrile butadiene rubber and Viton displayed the most significant change in all categories. Polytetrafluororethylene and polyether ether ketone were found to be the most resistant to all types of bio-oil in all conditions.