Grocery bills had begun to stabilize after a bruising stretch of inflation. Now, rising fuel and transportation costs threaten to make that relief short-lived. While food prices have managed to hold fairly steady this year, much of September's accelerating headline inflation number was driven by a 20.4% increase in energy prices — the largest hike since May, the US Bureau of Labor Statistics said Wednesday. Attacks on oil tankers and energy infrastructure in Iran, Saudi Arabia, and Russia have complicated the global supply of diesel, which is likely to raise transportation costs across the economy in the coming weeks and months.

Those increases in fuel and energy significantly impact the cost of producing and distributing food for grocery stores that are thousands of miles from the infamous Strait of Hormuz. Grocery chain Albertson's said on an earnings call Tuesday that its business is being squeezed by higher gas prices for US shoppers and higher diesel prices in its operations. And spice maker McCormick said earlier this month that it now anticipates 7% inflation in its financial forecasts, due in part to energy challenges.

"We're facing more costs, both in terms of raw packaging, but also freight, primarily freight costs due to fuel, as well as capacity constraints in the US," CFO Marcos Gabriel said on an earnings call. Food conglomerate Conagra likewise projected higher prices in its business through the remainder of the year due to accelerating fuel and transportation costs. Conagra's portfolio includes brands like Birds Eye, Marie Calendar's, and Slim Jim.

Even as gas prices have remained high this year, the reversal of many of Trump's tariffs meant that US shoppers were starting to see some stability — and a bit of relief — on grocery prices. Companies like Walmart and Costco said they were investing much of their tariff refunds into lower prices and better values for shoppers.

Some grocery retailers have moved ahead of shoppers' anxieties with targeted, preemptive cuts to lure consumers with purported deals. Discount chain Aldi said last month that it is rolling out approximately $86 million in discounts on fresh foods through November 3. Even regional players are using price cuts in their marketing. Ahold Delhaize's Stop & Shop stores in the Northeast lowered prices on thousands of items with bright yellow price tags touting the changes.

But the worsening outlook for energy is poised to complicate the progress consumers were starting to see on affordability this year. As of Sunday, AAA reported that the average price of regular gas in the US was $4.36 per gallon. At this time last year, that number was $3.09. Diesel prices have also skyrocketed, reaching $6.28 per gallon earlier this month. Shipping prices for tanker ships passing through the Strait of Hormuz have surged since the beginning of the war.

Earlier this month, shipbroker Gibson said tanker attacks in the Middle East hit their highest levels since the war began. News agencies reported Wednesday that a cargo ship sank after hitting a naval mine in the Strait of Hormuz. That leaves the grocery-price relief consumers had begun to see looking increasingly fragile.