Prices for diesel exhaust fluid remain stable in the U.S. but they are showing no signs of letting up in Canada with a string of monthly hikes, according to new figures from Integer Research, which analyzes a range of global commodities.

The U.S. national DEF truck stop average price decreased in April by one cent to $2.79 in per gallon, while the Canadian average increased to CA$0.81 per liter for the first time since October 2011.

The bigger hike in Canada is for bulk DEF deliveries, which are up for the firth straight month, with the average price increasing one cent from March to CA$0.50 per liter for full truckload deliveries and up two cents to CA$0.59 per liter for less-than-truckload deliveries.

The U.S. national average price for FTL and LTL bulk deliveries remained at $1.61 per gallon and $1.93 per gallon, respectively, in April.

The lowest average prices for all delivery modes were found in the Chicago and Cincinnati metropolitan areas while the highest average prices were found in Denver, Phoenix and Los Angeles areas.

DEF is used in most 2010 and later model year heavy-duty diesel truck engines to reduce the amount of nitrogen oxides released into the atmosphere.