The cost of meeting standards for conventional pollutant emissions is a perennial bone of contention in arguments over vehicle emission regulations. The public health benefits of the most stringent standards have been repeatedly and conclusively demonstrated, and the control technologies are readily available. Nevertheless, countries with the largest vehicle markets worldwide differ greatly in the rates at which they are willing to adopt the most stringent emission standards-and some of those whose populations would benefit most lag furthest behind the best achievable standards. Among the reasons often given for delaying the implementation of stricter standards is the extra cost added to the vehicle by the emission control system.As part of a two series paper, this paper addresses the cost of diesel light-duty emission control technology by regulatory level, from early stages to upcoming levels, and presents a comparison with gasoline emission control technologies. Focus is given to aftertreatment devices, especially diesel particulate filters and SCR systems. Technologies and costs are studied for the two main regulatory programs followed globally, the European and the U.S. emission standards. Part two of these emission control technology cost assessment paper series follows the methodology presented in part one. The report assesses the costs of required technologies in current terms, using both direct and indirect methods to account for technology changes, correct for inflation, and pull in feedback from experts. Estimates show that the cost of taking a 4-cylinder 2.0 L gasoline engine from Euro 1 controls to the most stringent proposed EU standard (Euro 6) is around US$370, whereas the cost of taking a 4-cylinder 2.0 L diesel engine from Euro 1 controls to Euro 6 standard is around $1600.