Diesel Hits $5.66 — Brent Crude Jumps to $108 on Iran Supply Shock

Why did diesel jump to $5.66 a gallon?

Diesel hit $5.66 per gallon nationally May 15 — 15 cents below the all-time record — as Brent crude oil climbed 2.1% to $107.97 a barrel. The Strait of Hormuz remains closed to oil tankers because of the ongoing war with Iran, preventing crude deliveries to customers worldwide and driving oil prices 54% above the roughly $70-per-barrel level seen before the conflict started. Patrick De Haan, head of petroleum analysis at GasBuddy, said the national diesel average appears to be plateauing short-term, with some easing in Great Lakes states this weekend, but warned another run at the record could happen down the road.

Brent crude's move to $108 marks the sharpest sustained oil-price spike since the pandemic supply shock. The closure of the Strait of Hormuz — a chokepoint for roughly one-fifth of global oil shipments — has kept tankers from delivering crude to refiners, tightening supply and pushing up the cost of every gallon a fleet burns. For a five-truck operation running 500 miles per day per truck at 6 mpg, the 54% jump in crude prices translates to roughly $1,400 more per week in fuel costs compared to pre-war levels, assuming diesel tracks crude movement proportionally.

Treasury yields climbed sharply May 15 as bond markets priced in prolonged inflation pressure from higher fuel costs. The yield on the 10-year Treasury rose to 4.56% from 4.47% the day before — a notable single-day move — and stands well above its 3.97% level from before the war. The 30-year Treasury yield is near its highest level since 2023 after breaking above 5%. Higher yields make truck loans, equipment financing, and working-capital lines more expensive, which slows fleet expansion and raises the cost of rolling over debt.

What happened to Fed rate-cut expectations?

Traders have abandoned virtually all expectations that the Federal Reserve will resume cutting interest rates in 2026, according to CME Group data. Some are now building bets that the Fed may hike rates this year to counter inflation driven by oil prices and tariffs. That marks a sharp reversal from earlier 2026, when markets had priced in multiple rate cuts. For small fleets, the shift means financing costs for new trucks, trailers, and working capital will stay elevated or climb further. A carrier financing a $150,000 truck at 7% instead of 5% pays roughly $3,600 more in interest over a five-year loan.

Brian Jacobsen, chief economic strategist at Annex Wealth Management, said strong corporate profits and a durable U.S. economy remain intact but warned "the path is unlikely to be smooth. Periods like this call for discipline more than hope." Many large U.S. companies have reported that customers continue spending despite higher gasoline prices, but household surveys show growing discouragement about the economy under pressure from both the war and tariffs.

How are fuel costs hitting freight demand?

U.S. stock markets fell sharply May 15, with the S&P 500 dropping 1.1% from its all-time high set the day before. The Dow Jones Industrial Average was down 408 points, or 0.8%, and the Nasdaq composite fell 1.6% from its own record. Technology stocks that had driven market gains for much of the year tumbled, with Nvidia — the face of the AI boom — dropping 3.6%. South Korea's Kospi index fell 6.1%, one of the sharpest moves globally, after briefly topping 8,000 for the first time.

The stock-market drop signals broader economic anxiety that typically precedes softer freight demand. When equity markets fall and bond yields climb simultaneously, shippers often pull back on inventory builds and delay non-essential shipments, which shows up in spot-market load counts within weeks. The combination of higher fuel costs eating into shipper budgets and tighter credit conditions from rising yields creates a double squeeze on freight volumes.

For owner-operators and small fleets, the fuel-price plateau De Haan described offers a narrow window to lock in fuel hedges or negotiate fuel surcharges with direct customers before another leg up. Fleets running dedicated lanes with fuel-surcharge clauses should verify that those clauses reset weekly and track the Department of Energy's diesel index — not a lagging monthly average — to capture the full cost pass-through. Spot-market carriers have less leverage but can prioritize shorter hauls that reduce total fuel burn per load and avoid lanes where backhaul rates don't cover the return trip's fuel cost at $5.66 per gallon.

What's the timeline for relief?

No end date for the Strait of Hormuz closure has been announced, and oil markets are pricing in an extended disruption. Brent crude at $108 reflects trader expectations that tanker traffic through the strait will remain blocked for weeks or months, not days. The 54% price increase from pre-war levels suggests the market sees no near-term resolution that would allow the roughly 21 million barrels per day that normally transit the strait to resume flowing.

Fleets should plan for diesel to stay above $5.50 per gallon through at least the end of May, with the risk of another attempt at the all-time record if crude climbs further or if refinery capacity tightens. The Great Lakes easing De Haan mentioned reflects regional supply adjustments, not a national trend reversal. Carriers operating in the Midwest may see a few cents of relief this weekend, but those gains are fragile and could reverse if crude prices continue climbing or if refinery maintenance schedules reduce diesel output.

The bond-market signal — 10-year yields up nearly 60 basis points since the war started — tells a longer story. Even if oil prices stabilize at current levels, the inflation they've already pushed into the system will keep the Fed from cutting rates in 2026. That means the cost of capital for fleets will remain elevated well into 2027, regardless of when the Strait of Hormuz reopens. Small fleets considering equipment purchases or lease renewals should model financing costs at 7% or higher and assume no relief from rate cuts this year.