The average U.S. price for on-highway diesel fuel has fallen six-and-half cents from a week ago to $3.781 per gallon, according to the latest price report issued by the Dept. of Energy’s Energy Information Administration (EIA). EIA also stated that the average price of on-highway diesel is now 17.3 cents lower than it was a year ago.

Diesel is now over $4.00 per gallon only in California ($4.066), although the West Coast ($3.991), New England ($3.974) and the Central Atlantic region ($3.909) closely trail the Golden State. Diesel is lowest in the Midwest ($3.696) and the Lower Atlantic region ($3.721) this week.

The national average price of regular gasoline is also down, having dropped four cents per gallon to $3.572 this week. The U.S. average gasoline price is now 14.1 cents lower than a year ago. Gasoline remains over $4.00 only on the West Coast ($4.093) and it is lowest on the Gulf Coast ($3.311).

According to EIA’s latest Short-Term Energy Outlook forecast, released last month, the agency expects that on-highway diesel fuel retail prices (which averaged $3.84 per gallon in 2011) will average $4.06 per gallon in 2012-- down nine cents per gallon from the previous month’s Outlook.

In 2013, EIA projects that diesel-fuel retail prices will decline to $4.03 per gallon-- eight cents per gallon lower than the previous Outlook.

EIA also pointed out that “movements in gasoline and diesel prices are driven primarily by changes in both crude oil prices and wholesale margins.” The agency noted that “wholesale diesel margins are robust during the forecast interval due to strong world-wide demand for the fuel.”

Indeed, stated EIA, those margins average 60 cents per gallon, similar to the 2011 average and higher than the previous five-year average of 52 cents per gallon, and that the “diesel wholesale margin for 2013 remains wide, averaging 59 cents per gallon.”

According to Denton Cinquegrana, executive editor of the Oil Price Information Service (OPIS), data tracked by OPIS shows that today’s diesel average is $3.8216 per gallon.

He told FleetOwner that that is “not the lowest of the year, but pretty close as the lowest I see in our database for 2012 is $3.8164, less than a penny away. And I expect we'll be seeing 2012 lows before the end of the week.”

Cinquegrana said the diesel trend is “absolutely pointing lower as oil prices have dropped significantly [recently] and inventories of diesel in the U.S. are fair. Current diesel stocks are about 12 million barrels behind where they were this time last year, but the market is not in a supply panic. Supplies are okay enough that the U.S. is exporting diesel still.”

As for what’s driving oil prices, Cinquegrana says it is all about macroeconomics. “European debt concerns, worries about China and about a possible double-dip recession in the U.S. are driving the market,” he explained. “A recession in any of these places would lead to less oil demand.

“Heating oil futures serve as a proxy for global diesel trends,” Cinquegrana added. “and they have been under pressure of late on concerns of slower economic activity.”