Abstract: Diesel in Chile receives a different tax treatment depending on its use. If diesel is used in industrial activities the diesel tax paid can be used as a credit against VAT and if diesel is used in freight or public transportation (basically trucks and buses) a fraction of gasoline taxes paid can be used as a credit against VAT. As a result of this different tax treatment firms have incentives to use “tax exempted” diesel in activities requiring “non tax exempted” diesel. This price wedge generates and opportunity for tax evasion. In this paper we analyze the impact of a tax enforcement program implemented by the Chilean IRS, where letters requiring information about diesel tax credits were sent to around 200 firms in 2003. Using different empirical strategies to consider the non-randomness of the selection of firms, we find that firms receiving a letter decreased their diesel tax credits by 16%.