Spanish drivers face this Tuesday, September 1, a new change in fuel prices, although its effects will be very different depending on what is in the tank. The Government activates the safeguard clause provided for diesel, which will allow maintaining during September a tax reduction of 20 cents per liter, while gasoline will continue with the schedule of gradual withdrawal of aid and will remain at only 5 cents per liter.
The difference is important because during August both gasoline and diesel have an ordinary reduction of 10 cents per liter in the Hydrocarbons Tax. From tomorrow, therefore, the tax relief for diesel increases by another 10 cents, while that for gasoline decreases by five. This means that the advice to wait until September 1 to fill the tank makes sense especially for diesel vehicles.
Why diesel will have a greater reduction
The mechanism was included in Royal Decree-Law 18/2026 approved at the end of June to respond to the increase in energy costs related to the crisis in the Middle East. The initial schedule contemplated gradually withdrawing the tax reduction: 15 cents per liter in July, 10 in August, and 5 in September. However, the Executive incorporated an automatic clause to prevent that withdrawal from coinciding with an extraordinary increase in fuel prices.
The condition was that the CPI of each fuel increased by more than 15% year-on-year in July. Diesel exceeded the limit, with an increase of 15.7%, while gasoline remained at 7.3%. The result is that diesel activates the protection and has a reduction of 20 cents during September; gasoline does not meet the requirement and maintains the originally planned reduction of five cents.
How much you can save if you wait to fill a diesel tank
The key to doing the math correctly is not to confuse the total reduction for September with the additional savings compared to August. Diesel will have a tax relief of 20 cents per liter, but it already enjoys 10 cents. Therefore, waiting until September 1 means an additional tax improvement of 10 cents per liter, as long as the other components of the price remain constant.
In a tank of 40 liters, that difference amounts to 4 euros of Hydrocarbon Tax; in one of 50 liters, to 5 euros; and in one of 60 liters, to 6 euros. As the VAT of 21% is also applied on a base that includes the special taxes, the theoretical impact on the final price may be somewhat higher: around 4.84 euros for 40 liters, 6.05 euros for 50 and 7.26 euros for 60, if the entire reduction is passed on to the pump.
If the comparison is made against the full tax, without any aid, the total reduction for September is 20 cents per liter: 10 euros less Hydrocarbon Tax in a 50-liter tank. But for those who are hesitating between refueling today or doing it tomorrow, the relevant saving is the change of 10 additional cents compared to August, not the full 20.
With gasoline, the opposite happens
Gasoline vehicles will not receive that improvement. During August, the tax reduction is 10 cents per liter and from September it will drop to 5 cents, so the tax component will increase by five cents per liter compared to this month.
Under equal market conditions, a 50-liter tank would bear 2.50 euros more in Hydrocarbon Tax than in August. If the effect of VAT is included, the theoretical difference at the pump would be approximately 3.03 euros. For 60 liters, it would rise to about 3.63 euros.
That is why, it cannot be stated that gasoline and diesel will automatically drop tomorrow. Tax-wise, diesel does improve, while gasoline loses part of the support it had in August.
Gasoline at 1.72 euros and diesel at 1.86 after a summer of sharp increases
The change comes after a summer especially complicated for drivers. At the beginning of the Return Operation, the average price was around 1.727 euros per liter for gasoline and 1.861 euros for diesel, according to data collected by RTVE. Gasoline has become more expensive by nearly 20% since the end of June and diesel by almost 24%.
This increase has also contributed to the rise in inflation. The preliminary CPI for August has been set at 4.3%, its highest level in more than three years, with fuels among the main contributors to the increase.
The safeguard clause precisely aims to prevent the withdrawal of aid from further exacerbating the increase in diesel prices. However, the mechanism uses the CPI of July as a reference, so it does not respond immediately to the variations that occur during August.
The tax reduction does not guarantee that tomorrow you will see exactly 10 cents less
There is also another important caution. The Government modifies the tax, it does not directly set the price that appears at each pump. The final price also depends on oil, refined products, the exchange rate, transportation, the margins of the companies, and the competition between stations.
Therefore, a gas station can modify its rate at the same time that the new taxation comes into effect, and the consumer could find a greater, lesser, or even no visible decrease compared to the price of the previous day. RTVE warns that the evolution of crude oil will remain decisive during September.
Even so, if we exclusively compare the effect of the taxes, the conclusion is clear: those who need to fill a diesel tank and can wait until September 1 will have an additional tax reduction of 10 cents per liter compared to August. Those who drive a gasoline car, on the other hand, do not gain a tax advantage by waiting: starting tomorrow, their discount is reduced from 10 to 5 cents per liter.