We develop an analytical and numerical multi-market model that integrates land, fuel, and food markets, and link it with an emissions model to quantify the importance of carbon leakage relative to the intended emissions savings resulting from the Renewable Fuel Standard (RFS) for conventional biofuels. The expansion of biofuels mandated by the RFS can increase or decrease GHG emissions depending on the policy regime being evaluated. For example, replacing the Volumetric Ethanol Excise Tax Credit (VEETC) with the RFS, as occurred at the end of 2011 when the VEETC was allowed to expire, would reduce emissions by 2.0 tgCO(2)e in 2015 for an expansion of ethanol of 11.4 billion liters. A policy regime consisting of the RFS alone would increase emissions by at least 4.5 tgCO(2)e for the same expansion of ethanol. Our findings highlight an important tension between land and fuel market leakage. Policy regimes that result in less land market leakage tend to lead to more domestic fuel market leakage per liter of ethanol added.