The compatibility of fueling infrastructure elastomers in bio-oil and diesel fuel was determined by measuring the volume swell and hardness before and after drying. The bio-oil was produced via fast pyrolysis from a blend of pine feedstocks. The elastomer materials included two fluorocarbons, six acrylonitirile butadiene rubbers (NBRs), fluorosilicone, styrene butadiene rubber, neoprene, polyurethane, neoprene, silicone, ethylene propylene diene monomer (EPDM), hydrogenated acrylonitrile butadiene rubber (HNBR), a blend of NBR and PVC (OZO), and a blend of epichlorohydrin and ethylene oxide (ECO). The majority of the elastomer materials (except for EPDM, SBR and silicone) exhibited higher volume expansion in bio-oil than in diesel. Excessive swelling was noted for the polyurethane, neoprene and three of the NBRs. In general, the higher polarity of these elastomers more closely aligned with the polarities of the bio-oil versus the diesel fuel. Conversely, EPDM, SBR, and silicone are relatively nonpolar and this matches the low polarity of the diesel fuel, which resulted in higher volume expansion in diesel, rather than the bio-oil for these four polymers. DISCLAIMER This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ). INTRODUCTION Fast pyrolysis-derived bio-oils are being evaluated as a renewable fuel for use in transportation, home heating, and energy production. 1 Fast-pyrolysis consists of rapidly heating (around 1000°C/sec) of biomass feedstock in the absence of oxygen. Liquid yields may reach 75% depending on feedstock type, reactor design and other processing variables. 2–7 The resulting oils have high viscosity and water content relative to petroleum distillates. Because the feedstock is biomass (typically pelletized wood), these fuels provide a pathway toward reducing the dependency on foreign petroleum, while utilizing a cleaner, and renewable, resource. However, before these fuels can become acceptable and commonplace, they must demonstrate acceptable compatibility with existing fuel systems and the associated infrastructure materials, both metals and polymers. The chemical profile of these fuels depends on the feedstock and can vary considerably (even among tree species). As a result, the composition of these oils can vary widely, but they usually consist of significant quantities of phenols, ketones, and other oxygenates (including short-chain carboxylic acids).