Why are diesel prices so much higher than regular gas?

The average price of a gallon of diesel fuel in the U.S. on Sept. 16, was $6.31, according to AAA. That's up from an average diesel price of $5.94 on Sept. 9, and $3.70 a year ago, the group said.

By comparison, the average price of a gallon of regular gas on Sept. 16 was $4.36.

Oil prices also spiked amid continued escalation in the United States–Israeli war against Iran. Futures for Brent crude oil, the international benchmark, reached about $106 per barrel Sept. 16. Futures for November delivery of West Texas Intermediate, the U.S. benchmark, traded at about $103 per barrel.

Patrick De Haan, head of petroleum analysis at GasBuddy, said in a social media post that gas and diesel prices were expected to continue rising as the war continues.

With that in mind, USA Today’s cars team took a look at what caused diesel fuel to cost more than gas.

Why is there a disparity?

Diesel fuel historically was cheaper than regular gasoline, except during exceptionally cold winters when there was greater demand for diesel and other heating oils, but that trend started reversing around September 2004, according to the U.S. Energy Information Agency.

The agency attributed the higher diesel costs to these three factors:

• Higher demand for diesel fuel

• Increased diesel production and distribution costs due to the transition to less-polluting, lower-sulfur diesel fuels

• Federal gas taxes are higher for on-highway diesel fuel, 24.40 cents per gallon, than the federal gas tax, 18.4 cents per gallon.

What are the effects?

Higher diesel costs translated to increased grocery prices for many consumers, because shipping companies usually make deliveries to stores in diesel-powered trucks. Higher shipping costs are passed on to consumers rather than being absorbed by grocery chains.

According to American Trucking Associations, which lobbies in Washington for major trucking companies, almost 73% of the nation's cargo freight was moved by diesel trucks in 2024, which is the most recent data the group made publicly available. That means 1.27 billion tons of freight was transported by trucks that now cost shipping companies a lot more to fill up.

Big rigs have tanks that can range in capacity from 120 to 150 gallons, according to the FreightWaves.com website. Such trucks average about 6 miles per gallon, according to the site.

Consumers squeezed

Consumer advocates say customers already were squeezed by higher prices caused by other factors like inflation before diesel prices started spiking this year.

“Since early 2021, American consumers have seen their family budgets getting squeezed more and more," David Holt, president of the Houston, Texas-based Consumer Energy Alliance, which lobbies for energy policies that benefit consumers, said in a statement.

"On top of the direct impact of excessively high gasoline and diesel prices, family budgets are crushed by the inflationary impact those fuel prices have on essential, everyday commodities like eggs, bread, milk, and clothing — all of which require diesel fuel to get to our markets or homes," Holt continued. "Simply put, when gasoline and diesel costs go up, the cost of everything goes up."

What vehicles use diesel?

Carmakers don't sell as many diesel-powered models as they once did. Most of the available diesel vehicles are large SUVs and pickup trucks.

Here are some popular vehicles with versions that still use the more expensive fuel, according to Carfax:

• Chevrolet Tahoe

• Chevrolet Suburban

• GMC Yukon

Here are some additional models with diesel versions that recently were discontinued but might still be for sale in used-car lots:

• Cadillac Escalade

• Jeep Wrangler

• Land Rover Range Rover

• Mazda CX-5