The average cost of on-highway diesel posted one of its biggest week-over-week declines of the year on Monday, hitting its lowest level since January 2011, according to U.S. Energy Department figures.

It fell 11.6 cents to $3.419 per gallon, down from its high so far this year of $4.021 hit in March. Compared to a year ago the price is 45.2 cents less.

Prices fell in all sections of the country over the past week, ranging from 5.8 cents in New England to as much as 15.1 cents in the Rocky Mountain region. Compared to the same time in 2013, diesel is down by as little as 34.8 cents in the Rocky Mountain region to as much as 59.7 cents in New England.

It currently ranges from a low of $3.314 in the Lower Atlantic states to a high of $3.504 in the Rocky Mountain region.

Likewise, gasoline prices are also down dramatically from levels earlier this year with the cost of regular grade gasoline falling 12.5 cents this week from last to an average of $2.554 per gallon.

Compared to a year ago the price is 68.5 cents less and is down from a high for the year of $3.704 hit in July.

It currently ranges from $2.328 in the Gulf Coast states to a high of $2.833 in the West Coast region.

A sharp drop in the price of oil has caused the recent decline in fuel prices as West Texas Intermediate crude fell on Monday by $1.90 in New York, settling at $55.91 per barrel, its lowest closing price since May 2009. Over the past six months it has fallen 48%. Overseas, Brent crude fell to $61.06 per barrel, its lowest price since July 2009.

The drop in oil prices has been caused by a surge in U.S. production of crude, continued high levels of oil production by OPEC member nations and declining worldwide demand. Some analysts predict prices will continue falling well into the New Year.