Soaring diesel prices force carriers to update fuel surcharges weekly instead of monthly

Diesel prices have been rising so fast that freight carriers need to update their fuel surcharge rates weekly instead of monthly, or else risk squeezing their profit margins , according to transportation management system (TMS) software provider Magnus Technologies.

That conclusion comes as Austin, Texas-based Magnus reported that the U.S. average retail diesel price rose to $6.29 a gallon in September, up $0.78 from the end of August and 68% above September 2025 levels. Those numbers came from the firm’s “September 2026 Diesel Fuel Snapshot” report.

In fact, September 2026 marked the highest monthly average in U.S. Energy Information Administration (EIA) weekly data dating back to 1994. All four September weeks priced above $5.00, bringing the 2026 total to 25 weeks above that threshold.

The speed of the price increase from August to September matters most for carriers whose surcharge programs reset monthly or are based on prior-period averages. When prices rise this fast, a surcharge priced off last month’s average trails what trucks are actually paying at the pump, and the difference comes out of carrier margin on every load until the surcharge table catches up. At 6.5 miles per gallon, a surcharge that trails the pump by $0.78 a gallon costs a carrier 12 cents a mile, or about $300 per truck on a 2,500-mile week.

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