WASHINGTON — 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.

Overall, prices in Canada have also dipped in recent weeks. Atlantic Canada diesel averages, which peaked as high as $1.70 a liter is some remote regions this past summer, now hover just over $1.30.

Prices are uncharacteristically higher in Alberta, Saskatchewan, and Manitoba because of a Prairie-wide diesel shortage. Prices in Southern Alberta — traditionally the lowest in Canada — are as high as $1.30, compared to a $1.20 average in Southern Ontario.