The average price of a gallon of on-highway diesel fuel was down again for the third straight week, according to the latest numbers from the U.S. Energy Department.

The average price fell by 0.014 cents per gallon to $2.87 per gallon, nationally. Prices are still down by $1.012 compared to this time last year.

Average diesel prices are down nationally for the third straight week since peaking at $2.914 per gallon.

Regionally, the largest decrease in price was seen in California-- where it was down 0.035 cents per gallon to 3.182 per gallon. Incidentally, California is also the location of the highest average price per gallon in the country. The smallest drop in prices were seen in New England with a barely registerable  0.003 cents per gallon decline to $3.073.

By contrast, the average price of a gallon of regular gasoline was up this week by 0.055 cents per gallon for an average of $2.835 per gallon. Last week, prices were flat on average but the price of gasoline had been on a seven-week spike prior to that.

The largest increase in the price of a gallon of gasoline was found in the Midwest region with an increase of 0.117 cents per gallon to $2.794 per gallon.

The sole regional decrease in the price of gasoline occurred in the West Coast region with a drop of 0.043 cents to $3.334 per gallon.

U.S. crude oil prices were on the rise this week as Tropical Storm Bill approached the oil-producing Gulf Coast, but production from offshore oil producing platforms have not been affected, according to a CNBC report.