The average cost of diesel has increased for the third consecutive week, hitting its highest level since early September, while oil crossed the century mark for the first time this year.

It moved up to $3.977 per gallon, an increase of 2.6 cents from a week ago and 10.4 cents more than when it last fell on Jan. 20, according to new figures from the U.S. Energy Department.

Compared to a year ago the national average price is 12.7 cents less. It’s also down in all regions of the country compared to the same time in 2013, except in the New England and Central Atlantic parts.

Prices increased in all parts of the country over the past week, except for the West Coast minus California, where it declined only 0.1 cent to $3.901 per gallon. The biggest increases were in the Central Atlantic and New England portions that make up the East Coast region, adding 8.2 cents for $4.363 and 6.4 cents for $4.369, respectively.

The two sections are, by far, the highest priced parts of the country, while the least expensive average diesel cost is in the Gulf Coast region, up 1.3 cents from a week ago, to $3.788.

Gasoline also increased over the past week, adding 1.7 cents, for a U.S. average of $3.309 per gallon. Compared to a year ago the price 30.2 cents less.

Prices range from a low of $3.086 in the Gulf Coast region to a high of $3.517 along the West Coast.

Meantime, the cost of crude in New York trading added 18 cents on Monday, closing at $100.06 per barrel and is up a around $3.50 over the past week.

The increase in oil has come as the result of frigid temperatures in parts of the U.S. as demand for home heating oil has jumped.