According to the International Energy Agency (IEA), the United States consumes 20 million barrels of crude oil per day (840,000,000 gallons)1. More than half of this quantity is imported. It is expected that by 2025 this quantity is expected to rise to 26 million barrels per day with an estimated sixty percent of the consumed quantity being imported. With the prices of oil to continue to be above $90/barrel, the expected annual expenditures on imported oil is estimated to be >$250 billion. With the cost of fossil fuel continuing to increase as its quantity is depleted, there is a strong driver for continued investment in renewable fuel sources. One such approach is the use of plant-based feedstock to augment conventional fossil fuel for diesel applications. Use of such feedstock has given rise to the biodiesel fuel industry (BD).Studies have documented fuel-oil dilution issues in diesel applications. The presence of BD in the engine oil reduces the life of the oil as well as its effectiveness2. Since the BD is a naturally miscible in engine oil several undesirable characteristics can result. These negative effects include: reduced oil viscosity; increased engine wear; acid formation leading to corrosion; low oil pressure. This study will focus on the effects of bio-derived diesel fuel (BD), B20 and B100, and its effects on 15 common sealing elastomers. In addition, the effect of 5% biodiesel B20 and B100 dispersed in conventional 15W-40 engine oil will be examined for its effects on these same sealing materials.