If fuel prices have seemed higher at the pump than normal, you’re not imagining things. The average price of a gallon of diesel fuel in the U.S. hit more than $3.15 last week, and in many parts of the country it is much higher than that.

The price of diesel fuel has been steadily increasing for the past six weeks — up 18.5 cents since March 19. There has also been a long-term trend toward higher prices since they bottomed out at under $2 per gallon in February 2016. In just the last year, the average price has jumped more than 57 cents per gallon.

Prices in all parts of the U.S increased last week, with California having the highest diesel prices by far at $3.834 per gallon. The lowest prices in the country were found in the Gulf Coast region at $2.946 per gallon.

The largest increase in prices last week occurred  in the Midwest region, where prices rose by 3.6 cents per gallon. The smallest increase was in the Gulf Coast region at just 1 cent per gallon.

Global crude oil prices have been on the rise in the past month, caused by increased tension in the Middle East and the possibility that the U.S. will end its nuclear deal with Iran.

In a televised address on April, 30, Israeli Prime Minister Benjamin Netanyahu accused the Iranians of violating its agreement to suspend a nuclear weapons program. If the Iran nuclear deal falls through, that would mean increased sanctions on the nation which could reduce the oil supply by as much as 500,000 barrels of oil per day, according to a Marketwatch report.

In addition, Saudi Arabia recently signaled its intention to try to push crude oil prices back up to around $80 per gallon.

Oil prices closed higher on Monday, with June West Texas Intermediate crude oil rising to $68.47 a barrel on the New York Mercantile Exchange, while June Brent crude prices rose to $75.17 a barrel on ICE Futures Europe, a new 52-week high and the most since late 2014.

Related: Prepare Your Fleet Now for Higher Fuel Prices Later