Sulfur in gasoline: what car owners should know about it

The country’s oil refineries have been allowed to temporarily switch from Euro-5 to Euro-3 standard gasoline – let’s figure out what this “fuel downshifting” threatens and whether it can be fought with improvised means?

There was, I recall, a dialogue in the cult film “Election Day”: “Do you know where I can find a European power outlet? – In Europe…”. Indeed, the Euro-5 fuel standard came into use in that very Europe back in 2008, while here it only arrived in 2016. Before that, Euro-3 fuel was massively present on the market, and the transition period stretched over years (the Euro-4 standard, which was in effect in Europe from 2006 to 2009, was never really introduced here at all). And we never made the switch to Euro-6, which is current in many countries, and now, apparently, we won’t be switching anytime soon.

The other day, the Russian government allowed oil refineries to release gasoline and diesel fuel with Euro-3 class indicators onto our market. Although in fact it didn’t “allow” but “extended the permission”: such a relaxation in fuel quality was made back in autumn 2025, and now its effect has merely been prolonged. The measure supposedly should help increase the amount of fuel on the market, but the news unpleasantly stunned domestic car owners. Not only is gasoline nowhere to be found in places, but now even the gasoline that isn’t there will be of poor quality.

What is the chemical difference between the “euros”? Despite the fact that these standards include many parameters, they are all mere trifles against the backdrop of the main factor – the permissible amount of sulfur in milligrams per kilogram of fuel. Euro-3 allowed up to 150 mg/kg, while Euro-5 allows no more than 10 mg/kg. The difference is significant – 15 times.

In gasoline, sulfur is not contained in the form of poorly soluble yellow crystals, which some know from school, hobby, or professional chemistry, but in the form of mercaptans and sulfides. They dissolve well in fuel, and therefore there is essentially no problem of them settling in the “cold” part of the car’s fuel system. Sulfur from Euro-3 gasoline will not clog your fuel pump, fuel lines, pressure regulators, absorber system, or other elements. In fact, even the risk of damaging injectors in a traditional multi-point injection system is minimal.

Problems begin in the “hot” part of the engine. A large amount of burning sulfur generates an increased amount of carbon deposits on the piston crown, the upper part of the combustion chamber, and on the valves. The injector nozzles of direct injection systems operating in the hot zone become contaminated, and the fine pores of catalytic converters typical of advanced modern engines can also clog faster. The acid formed when sulfur combustion products combine with moisture from atmospheric air causes corrosion in the cylinders while the car sits idle (indeed, if anyone remembers the so-called “acid rain,” a sign of the ecological problems of the 90s – well, that’s exactly it). And crankcase gases saturated with sulfur combustion products actively oxidize engine oil, reducing its service life and causing an increased amount of varnish deposits under the valve cover, in the EGR system, and so on.

What can be done? Well, the impact of a tenfold increase in sulfur content probably cannot be completely eliminated with little effort, but some relatively effective measures can be taken.

It is useful to reduce engine oil change intervals, switching if possible to synthetics with a higher Total Base Number (TBN) – this indicator precisely indicates the amount of components in the oil responsible for neutralizing acidic elements that enter the lubricant with crankcase gases. You should check the cleanliness of the EGR system more often and prevent clogging and failure of its valves. It is advisable to use specialized cleaning fuel additives capable of reducing carbon formation in the combustion chamber, on direct injection injectors, and in catalytic converters.

To raise the level of erudition a bit, let’s understand what the process of removing sulfur from gasoline at a refinery actually involves and why, at the current quite high level of petrochemical development, this still represents a certain problem and ground for research by scientists around the world.

It’s good when the oil is high-quality, light, and low-sulfur, but often refineries receive difficult-to-process, low-quality feedstock – heavy high-sulfur oils. The fuel obtained from them has to be cleaned of sulfur.

Today, the main industrial method is hydrotreating, which effectively removes sulfur compounds but requires high temperatures, pressure, and the use of hydrogen. In other words – it is time-consuming and expensive. And even then, difficult-to-remove sulfur compounds remain, so the search for alternative purification methods is constantly ongoing worldwide.

One such method was recently developed by chemists from Lomonosov Moscow State University and Gubkin Russian State University of Oil and Gas: oxidative desulfurization.

The main idea is the development of an effective and stable catalyst for the process, allowing petroleum fractions to be purified of sulfur compounds at virtually room temperature, without the need for strong heating that drastically complicates and increases the cost of the process.

An experimental complex-structured catalyst made of aluminum oxide, molybdenum oxide, sulfo groups, and hydrophobic organic molecules oxidized 78% of sulfur-containing compounds in just 15 minutes at a temperature of 25°C, which is an excellent indicator for the industry. Moreover, the process proved to be selective – the oxidation did not affect valuable hydrocarbons.

And now we can descend from general and theoretical matters back down to earth, to our grave sins and applied tasks. Probably few have missed the latest news about how gullible Russian drivers are buying “miracle tablets” on marketplaces that promise to turn water into wine. More precisely, 92-octane gasoline into 95-octane, and 95-octane into 98-octane.

No, of course, effective preparations for raising the octane number do exist, but these are, alas, not a penny tablet per tank, but a can of about 300-400 milliliters, designed for 50-60 liters of fuel and costing quite a lot. The question is different: is there anything against sulfur? So that you pour it in – and done! And how do you determine what kind of gasoline you’ve filled up with – Euro-3 or still Euro-5? How much sulfur is in it? A petrochemical engineer from Moscow State University, Argam Akopyan, explains again:

As for household determination of sulfur content in gasoline, there are virtually no reliable and safe methods for the average consumer. Modern fuels differ in sulfur content at levels that require specialized laboratory equipment. Therefore, it is practically impossible to determine by appearance, smell, or simple household tests whether gasoline corresponds to the conditional Euro-3 or Euro-5 level.

It is also impossible in garage conditions, using available household means, to significantly reduce the sulfur content in gasoline, even if the seller of miracle chemicals on a marketplace hotly assures you otherwise. Sulfur compounds are in a dissolved state in the fuel and represent fairly stable organic molecules. They cannot be removed by simple settling, filtration, or by adding any household reagents to a canister or fuel tank. Sulfur removal is a complex oil refining task and requires special technological processes.

But overall, there is no need to dramatize the situation. If we are talking about the temporary use of fuel of a lower environmental class, this does not automatically mean serious problems with the car. However, the global trend over recent decades has been precisely the consistent reduction of sulfur content in motor fuels, since this allows reducing the environmental burden and ensures more efficient operation of modern exhaust gas aftertreatment systems.