By Mónica Cordero
The national average for a gallon of on-highway diesel reached $6.20 on Oct. 5, following a sharp increase that began in March and peaked in September, according to U.S. Energy Information Administration data published by the Department of Agriculture.
Diesel powers nearly every farm field operation, from planting and spraying to fertilizing and harvesting. Tillage requires the most fuel and is expected to account for the largest share of farm fuel expenses during the 2026 growing season, according to a South Dakota State University publication.
The rise in diesel prices coincided with disruptions to global oil supplies following the start of the conflict with Iran on Feb. 28 and the closure of the Strait of Hormuz. The narrow waterway between Iran and the Arabian Peninsula is one of the world's most important oil transit routes. An average of 20 million barrels of crude oil and petroleum products passed through the strait each day in 2025, accounting for about a quarter of global seaborne oil trade.
Damage to refineries in the Middle East and Russia has reduced global refining capacity, while the closure of the Strait of Hormuz has reduced the amount of crude oil reaching the market. Demand for gasoline and diesel has declined, but not enough to offset the tighter supply, according to the American Fuel & Petrochemical Manufacturers.
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