Average diesel fuel prices at the pump decreased for the sixth week in a row, according to the latest numbers from the Energy Department.

The average price of a gallon of on-highway diesel fuel dropped 5.4 cents last week to $2.284, hitting a new low for the year. The price is 99.7 cents cheaper than it was a year ago.

There were significant drops in all parts of the U.S., with the largest decrease hitting the Rocky Mountain region at 7.1 cents. The smallest drop was in the Gulf Coas, at 3.1 cents.

Gasoline prices also fell for the week, though by a smaller margin. Average prices dropped 1.1 cents, settling at $2.026 per gallon. The price is 37.7 cents cheaper than the same period last year.

The largest decrease in prices was in the Midwest region, at 5.5 cents, while the West Coast actually saw a significant increase in prices, at 5.6 cents per gallon.

Crude oil prices were trading at near 11-year lows on Dec. 21 as global supply continues to outweigh demand, according to a Wall Street Journal report.  

Despite domestic oil production significantly increasing this year, OPEC has refused to cut its production output. That's led to a free fall in the price that crude oil is trading for on the stock market. Brent Crude Oil fell to around $36 per barrel in global trading, reaching its lowest point since 2004.