The average price of diesel continued its downward trend for the fourth week in a row, slipping 2.1 cents
, according to the Department of Energy. Trucking's main fuel landed at $2.601 this week, after dropping a total of 7.3 cents since the end of August.

Prior to the declines, diesel had gained 17.8 cents since July 20. This week's average is still $1.358 below the price during the same week last year, when it was $3.959.

California experienced the highest prices of diesel this week, with an average of $2.807, followed by the West Coast and Central Atlantic regions, at $2.742 and $2.714, respectively. The Gulf Coast and Lower Atlantic regions saw the lowest prices, at $2.525 and $2.552, respectively.

Meanwhile, gasoline fell another 5.3 cents this week to $2.499, its seventh consecutive drop. Since mid-August, the fuel has slipped 14.8 cents. The price is still $1.133 below the price during the same week last year.

Following reports that Iran was test-firing missiles and U.S. equities were on the rise, U.S. oil saw a boost of 82 cents, landing at $66.84 a barrel Monday, according to Reuters.