The Department of Energy's Weekly Pump Price survey shows diesel fuel tumbled 4.6 cents a gallon from last week's national average price.
This week's national average price stands at $3.964 per gallon, the DOE's Energy Information Administration said on Monday.

While worldwide demand for diesel has refiners producing as much of the stuff as they can, one of the "byproducts," gasoline, continues to suffer gluts in supply as well as weakness in demand. That explains the 6.1-cent drop in gas prices from last week's DOE average. The national average price for a gallon of gas this week is $3.307 a gallon.

Diesel fuel remains more than 80 cents higher than it was a year ago, an nearly 25 cents a gallon higher than it was two months ago.

Meanwhile in the oil market, crude oil is on the upswing again, thanks to geopolitical worries begat by unrest in Syria, and the prospect of additional sanctions against Iran.

Iran exported 2.2 million barrels of oil a day last year, according to the U.S. Energy Information Administration, making it the world's third-largest oil exporter. The EU as a whole was the second-biggest recipient of that oil. And while Syria itself isn't a major oil producer, the scale of the uprising there has fed concern that the popular unrest in the region could spread to major oil producers like Saudi Arabia.

All that uncertainty tends to push prices higher, and oil's performance on Monday seems to bear that out. Light, sweet crude for January delivery settled up $1.44, or 1.5%, at $98.21 a barrel on the New York Mercantile Exchange. Nymex crude touched an intraday high of $100.74 a barrel, marking the contract's first foray into triple-digit territory since Nov. 18. The rally cooled as the trading day went on.

(Dollars per gallon, including all taxes)

East Coast: 3.953, Last week: -0.031, Last year: 0.787
New England: 4.045, Last week: -0.011, Last year: 0.808
Central Atlantic: 4.057, Last week: -0.043, Last year: 0.769
Lower Atlantic: 3.882, Last week: -0.036, Last year: 0.774
Midwest: 3.949, Last week: -0.061, Last year: 0.805
Gulf Coast: 3.859, Last week: -0.044, Last year: 0.781
Rocky Mountain: 4.094, Last week: -0.050, Last year: 0.822
West Coast: 4.142, Last week: -0.049, Last year: 0.842
California: 4.224, Last week: -0.047, Last year: 0.896

Canadian diesel prices remain high this week because of the shortage in diesel production at western Canadian refineries. Eastern refineries are unaffected by the shortage. Below is the Canadian average price as well as highs and lows around the country as noted in MJ Ervin & Associates / Kent Marketing Services Weekly Pump Price Survey for the week of Nov. 22.

Canadian average 134.1/liter ($5.08/US Gal equiv.)
High: 149.6/liter ($5.64/US Gal equiv.) noted in Labrador City, Newfoundland
Low: 124.2/liter ($4.69/US Gal equiv.) noted in Red Deer, Alta.