The average price of a gallon of diesel fell almost 3 cents this week to $2.219, according to weekly figures from the U.S. Energy Information Administration.
That's $1.061 less than the average a year ago. Diesel prices have not been this low since mid-2005.
The highest prices were seen in the New England region, with an average of $2.576; the lowest in the Gulf Coast region at $2.156, followed by the Midwest at $2.173.
Meanwhile, crude oil prices fell below $40 a barrel Monday, closing at $39.56 a barrel, the lowest close since Jan. 20, when oil settled at $38.74 a barrel. This is despite oil cartel OPEC's actions to cut production. Abdullah al-Badri, secretary-general of OPEC, told reporters that about 80 percent of the previously agreed-upon cuts were complete, according to CNN Money.