Diesel fell for the third time in four weeks, dipping 1.5 cents to $3.988 per gallon, the Department of Energy reported.
Diesel has fallen three of the past four weeks, but it has been on a cost run-up since Jan. 27 when the average retail price was $3.904.
Diesel is 1.8 cents below the corresponding week last year.
Gasoline, meanwhile, rose 0.2 cent to $3.549 a gallon.
Each week, DOE surveys about 400 diesel filling stations and 800 gasoline stations to compile national average prices.