Costco has doubled the price of its Kirkland Signature full synthetic motor oil from $30 to $57.99 and capped purchases at two bottles per customer per week as crude oil trades around $100 a barrel and supplies tighten. U.S. diesel prices have topped $6 per gallon for the first time, reaching $6.06. Refiners are prioritizing higher-margin gasoline and diesel output, constraining the availability of motor oil.

AAA data put the U.S. national average at $4.07 for gasoline and $5.47 for diesel, up from $3.14 and $3.69 a year earlier. That translates to roughly a 30% increase for gas in August 2025 and a 48% jump for diesel. A July estimate from the Joint Economic Committee said higher prices since Republicans began the war with Iran have cost Americans more than $56.4 billion in total, or $477 per household. The additional household costs are highest in states such as Alabama and Utah and lower in places including Hawaii and Oregon.