Diesel prices have continued a month-over-month and year-over-year steady rise. National average diesel fuel prices were $3.23 for the month of September, according to WEX. This is 5 cents higher than August and 49 cents higher than September 2017.

According to the EIA, West Texas Intermediate (WTI) crude futures prices rose by $1.17 per barrel during the week ended Sept. 14. Gasoline and diesel futures prices fell, but this did not appear to filter through to retail prices during the week ended Sept. 17.

State-by-state, Mississippi had the lowest diesel fuel prices at $3.03 per gallon with Hawaii experiencing the highest diesel prices of $4.26 per gallon, followed by California at $4.12 per gallon for diesel fuel, according to the AAA. 

Domestic crude inventories grew by 6.5 million barrels last week, according to the EIA. Total crude inventories now sit at 416.4 million barrels, marking the fourth week of consecutive growth and highest level since late June.

The larger-than-expected growth in crude levels jolted the market, which had seen prices steadily rising due to concerns about U.S.-Saudi Arabia relations and upcoming U.S.-imposed sanctions on Iran’s crude exports, according to AAA. With continued worries about global crude supply and demand this fall, more growth in total crude inventories could reduce concerns and push crude prices lower in the coming weeks if the trend continues.