According to AAA, the U.S. national average retail diesel price was about $6.23 per gallon on September 14, 2026 (AAA listed $6.2301 on its national fuel-price tracker).
That level was widely reported as a record national average, up from about $6.20 the previous day and about $5.90 a week earlier. For comparison, the same AAA-linked reporting put the year-ago national diesel average near $3.69 per gallon.