The national average retail diesel price fell 5.3 cents to $4.004 for the week ended Monday, May 14.
For the first time since 2009, the average diesel price is lower than it was during the same week the year before.
Diesel will average $2.95 this year and $3.12 in 2011, the agency said.
For the first time in 17 months, the national average retail price of a gallon of diesel topped $3.
For the first time in six weeks, the national average retail price of a gallon of diesel fell this week.
Compared with a year ago, the national average price is 90.7 cents a gallon higher.
All regions except New England reported sharply higher prices.
The national average price gained 2.9 cents to $2.861, according to the Department of Energy.
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