In the first week of the year, diesel prices continued to rise, extending a 6-week streak of increases, according to the latest numbers from the Energy Department.

The average price of on-highway diesel fuel in the U.S. increased 1.1 cents last week, rising to $2.597 per gallon at the pump. The price is now 42 cents higher than it was in the first week of 2016.

Increases were relatively small in most regions of the U.S. with the largest change hitting the Central Atlantic states with a 3.7-cent bump. Prices were actually down in the Gulf Coast region last week, falling by 0.3 cents.

The average price of regular gasoline was also up by 1.1 cents last week, increasing to $2.388 per gallon at the pump. The price of gas is more than 39 cents higher than it was in the same week a year ago.

By region, the largest increase in gas prices was on the West Coast, where prices jumped 2.9 cents per gallon. Prices were down in Midwest region, though not by much, falling 0.3 cents per gallon for the week.

Crude oil prices started the week at a 3-week low due to concerns over increased U.S. production and exports from Iraq, according to a CNBC report.

While the oil market was up thanks to an agreement between OPEC member countries and Russia to reduce or freeze oil production output, the higher oil prices had the effect of encouraging more American oil production. This has so far offset the expected gains from reducing global oil production to meet lower demand.