The adjustment affected approximately one-quarter of Hyundai 2011-13 model year vehicles, reducing their combined city/highway fuel economy by 1-2 miles per gallon (mpg). As part of the agreement, Hyundai will pay a $56.8 million civil penalty, forgo the use of approximately 2.7 million greenhouse gas (GHG) emission credits – the credits representing the difference between original and restated emission data – and continue to implement a series of measures including the formation of an independent certification test group to oversee the automaker's fuel economy testing, training, data management and reporting.