EPA is taking final action to establish nonconformance penalties (NCPs) for manufacturers of heavy heavy-duty diesel engines (HHDDE) in model years 2012 and later for emissions of oxides of nitrogen (NO<INF>X</INF>) because we have found the criteria for NCPs and the Clean Air Act have been met. The NO<INF>X</INF> standards to which these NCPs apply were established by a rule published on January 18, 2001. In general, NCPs allow a manufacturer of heavy-duty engines (HDEs) whose engines do not conform to applicable emission standards, but do not exceed a designated upper limit, to be issued a certificate of conformity upon payment of a monetary penalty to the United States Government. The upper limit associated with these NCPs is 0.50 grams of NO<INF>X</INF> per brake horsepower-hour (g/bhp-hr). This Final Rule specifies certain parameters that are entered into the preexisting penalty formulas along with the emissions of the engine and the incorporation of other factors to determine the amount a manufacturer must pay. Key parameters that determine the NCP a manufacturer must pay are EPA's estimated cost of compliance for a near worst-case engine and the degree to which the engine exceeds the emission standard (as measured from production engines). EPA proposed NCPs for medium heavy duty diesel engines. However, EPA is not taking final action with regard to NCPs for these engines at this time because EPA has not completed its review of the data and comments regarding these engines.