Prices for diesel exhaust fluid are stable in both the U.S. and Canada.

The national average price of DEF at truck stops islands was $2.79 per gallon in the U.S., a decline of one-cent from the month before, which has been the average price since November 2012, according to a new report from Integer Research and its website.

In Canada, the price remained unchanged at 80 cents per liter, where it has been since October 2011.

The national average for tote refill prices dropped four cents in the U.S. to $1.87 per gallon and one cent in Canada to 55 cents per liter.

Metropolitan area located in the West Coast and in the Central & Southern region posted the highest average prices, while St. Louis, Mo. registered the lowest average prices amongst all areas covered this month.

DEF is used in diesel engines with selective catalytic reduction (SCR) to lower NOx (nitrogen oxide) concentration in emissions.