Portugal adjusts fuel taxes as diesel rises four cents and petrol falls five cents

Opposing price paths for diesel and petrol

Portuguese motorists will face diverging prices at the pumps starting Monday, 14 September 2026. Projections by the Automóvel Club de Portugal initially pointed to a six-cent drop per litre for 95-octane petrol and a four-cent increase for simple diesel. However, an order published in the Diário da República by the government on Friday afternoon altered the extraordinary tax rates on petroleum products (ISP), moderating the market shifts. Under the revised fiscal terms, petrol will decrease by approximately five cents per litre, while diesel will increase by roughly 3.9 cents per litre.

Fiscal intervention and tax mechanics

The government's mechanism adjusts the ISP rates to offset variations in value-added tax revenues caused by price fluctuations. For 95-octane petrol, the state reduced the extraordinary ISP discount by 0.956 cents per litre, effectively absorbing nearly one cent of the anticipated relief and leaving the average projected price near 2.050 euros per litre. Conversely, the ISP discount for diesel was increased by 0.109 cents per litre, leaving the pump rise virtually untouched at an expected average of 2.151 euros per litre. The divergence will widen the price gap between diesel and petrol across domestic filling stations.

Global oil markets and shipping disruptions

The split trajectory reflects distinct international market drivers. Petrol costs are easing following the conclusion of the United States summer driving season, which traditionally relieves wholesale demand. In contrast, crude oil and diesel remain under intense pressure due to geopolitical tensions in the Middle East and the war involving Iran. Tanker traffic in the Strait of Hormuz, a conduit for roughly 20% of global oil and liquefied natural gas, faces severe disruption. In addition, Houthi advances along the Red Sea coast in Yemen and the Bab al-Mandeb strait continue to threaten critical shipping lanes toward Saudi Arabia.

If the forecasts for next week are confirmed, the average price of diesel will rise to 2.15 euros per litre, while petrol drops to 2.04 euros per litre.

Fiscal mitigation and state support packages

International crude benchmarks experienced sharp volatility throughout the week, with European benchmark Brent crude rising past 100 dollars per barrel to touch nearly 107 dollars on Thursday before trading around 104 dollars on Friday. In Portugal, the extraordinary ISP mitigation framework carries an estimated fiscal revenue cost of 777 million euros, according to the Conselho das Finanças Públicas. To further buffer supply, the executive previously authorized the release of up to 10% of national strategic fuel reserves and imposed a 33% contribution on extraordinary corporate energy profits. The government currently maintains a 10-cent discount per litre on agricultural diesel and has scheduled additional support measures next week for taxis, transport operators, volunteer firefighting associations, and private social solidarity institutions.