The average price of a gallon of on-highway diesel plummeted 21.6 cents this week as oil prices fell below $80 a barrel Tuesday.

Weekly figures from the U.S. Energy Information Administration put the national average of diesel at $3.659 as of Monday, Oct. 13. The lowest average was reported on the West Coast, at $3.622; the highest in the New England region at $3.892.

Concern about demand because of a slowing economy in the U.S. and in other countries has pushed oil prices down about 44 percent from a record high of $147.27 a barrel in mid-July.