EU diesel became the most expensive fuel at the pump on September 21, when the European Commission’s weighted average reached a record €2.226 per litre, 13.4 cents above Euro-super 95 petrol and about 40% above late-February levels. The increase followed the conflict involving the United States, Israel and Iran, damage to Middle Eastern energy infrastructure, restrictions on shipping through the Strait of Hormuz and attacks on Russian refineries, which tightened refined-diesel supplies. Transport & Environment estimates that higher road-fuel prices added €53 billion to European Union costs over the 28 weeks to September 6 compared with the same period a year earlier, adjusted for inflation; diesel accounted for €40 billion and average daily transport costs rose by €270 million. Portugal illustrates the wider impact: mainland standard diesel increased from €1.596 per litre on February 28 to €2.219 on September 27, while standard 95-octane petrol rose from €1.681 to €2.113. Transport, fisheries, agriculture, construction, manufacturing, retail and medicine distribution warned of higher operating costs, margin pressure and eventual increases in consumer prices. Taxes averaged €0.861 per litre, or 38.6% of the EU diesel pump price, while European Central Bank experts estimated refining margins contributed €0.41 per litre in the third week of September. Governments including Germany, Czechia, Spain and Portugal announced or extended relief measures, but the outlook remains dependent on the conflict, Hormuz shipping and global refining activity.