Magnus Technologies ("Magnus"), released the September 2026 Diesel Fuel Index, a quarterly market intelligence report tracking diesel price movement and its real-world impact on carrier margins.

The report found that U.S. average retail diesel prices fell through June before reversing sharply, with the week of July 20 producing a $0.34 per gallon jump, the largest single-week move since March. Prices climbed nearly every week after, touching $5.65 per gallon on August 24, a new high for the year, representing a 52.4% increase, or $1.94 per gallon, over the same week in 2025. Diesel closed at or above $5.00 per gallon in every week of August, bringing 2026's total to 21 weeks above that threshold.

Diesel has now swung sharply in both directions twice in five months, and carriers on quarterly surcharge resets have been shielded through most of the summer by rates still locked to the second quarter's elevated average. That protection is thinning fast as those resets roll into the fourth quarter.

The report is accompanied by the Magnus Fuel Gap Report, which models the impact of August's price swing on a representative 55-truck Texas carrier. The analysis found that a carrier on a weekly, index-based reset faced a worst one-week exposure of approximately $7,150, while a carrier on the market's most common structure, a monthly reset, left roughly $53,600 unrecovered over the course of August. A carrier on a quarterly reset has left about $14,000 unrecovered since mid-August, a gap the report notes is on track to widen sharply once quarterly resets roll into the fourth quarter.

The September 2026 Diesel Fuel Index is the second edition of Magnus Technologies' quarterly diesel market intelligence series.