Rising biofuel use in the United States has raised questions about the interactions between energy and agricultural commodity prices. This expansion of use has been attributed, in part, to tax credits and the Renewable Fuel Standard (RFS). These interventions can lead to questions about whether public policy has helped generate links between energy markets and agricultural markets, with the potential consequence that volatility in one market can be communicated to the 29 other. In this study, we derive theoretical relationships among petroleum, biofuel, and 30 agricultural commodity prices in the context of biofuel mandates, then apply time series methods 31 to estimate the strength of these links. 32 Studies that use historical data often represent market conditions when there were only very small shares of biofuel in liquid fuels and very small shares of feedstocks devoted to biofuel production. In the case of ethanol and corn, for example, the current shares are on the order of ten times their levels in the early 1980s (Figure 1). A key question, then, is whether rising biofuel use has created strong links between petroleum product prices and biofuel feedstock prices. If so, then this finding might lead decision makers to consider the potential for biofuel policies to achieve objectives relating to energy security and greenhouse gas emissions while putting greater weight on impacts of such policies on agricultural commodity price levels and volatility. If 41 biofuels do not create a strong link between petroleum and agricultural crop markets, then the 42 possible impacts on producers and other consumers of agricultural commodities might not be a 43 serious consideration. 44 45