More: "The cost of diesel gets into just about everything," KPMG chief economist Diane Swonk said in a recent interview.

"From running a farm ... [to the] cost of food, but also everything across the economy that's shipped," she said. When diesel prices rise, everything "gets that extra fee tacked onto it."

Swonk predicted that the high cost of diesel will be an "inflationary problem" for months to come.

Since late July, diesel prices have been rising higher and faster overall than the cost of regular unleaded gas.

That's because key refineries that produce it have been knocked offline or destroyed, both in Eastern Europe " where the Ukraine-Russia war still rages " and in the Middle East.