The price of diesel fuel in the U.S. increased to its highest point since June of 2015, according to the latest numbers from the Energy Department.

The average price of on-highway diesel fuel jumped 6.3 cents last week, topping out at $2.882 per gallon at the pump. The price is now 41.2 cents more expensive than it was in the same week a year ago.

Prices were up in all major regions of the U.S. The largest increase hit California with a staggering 35.6-cent rise in a single week. During the same week, California instituted a new fuel tax hike that increased prices by 20 cents per gallon.

The smallest change was recorded in the Rocky Mountain region where prices rose just 2.2 cents per gallon for the week.

Gasoline prices were up by a similar amount, increasing 7.3 cents last week to $2.561 per gallon. The price is currently 32.8 cents higher than it was in the same week of 2016.

The largest increase in gas prices was on the West Coast where, prices increased 12.1 cents for the week, again coinciding with a fuel tax increase in the state. The smallest change was in New England, where prices rose just 1 cent.

The price of crude oil hit a two-year high on Nov. 6, after news of a purge of important political figures in Saudi Arabia caused the market to spike, according to a CNBC report. In the ensuing market trading, crude oil prices hit $64 per barrel.

While there may be some parallels between the price spike and an important oil-producing country's political turmoil, analysts pointed to a general sense of geopolitical uncertainty as a driving force in the price increase.