Leakage in the fuel market differs, depending on whether ethanol production is determined by a tax credit or consumption mandate. Two components of market leakage are distinguished: domestic and international. Leakage with both a tax credit and a consumption mandate depends on market elasticities and consumption/production shares, with the former having a bigger impact. Leakage is also more sensitive to changes in market supply and demand elasticities in the country not introducing biofuels. Although positive with a tax credit, market leakage can be negative with a consumption mandate, meaning that one gallon of ethanol can replace more than a gallon of gasoline. We also show that being a small country biofuels producer does not necessarily mean that leakage for this country is 100 percent. Our numerical estimates show that one gallon of ethanol replaces approximately 0.2-0.3 gallons of gasoline in the U.S.