Fuels, Petrols.....The Difference Between Unleaded, Diesel, Super & Gas


Oct 01st, 2019

Fuels, Petrols.....The Difference Between Unleaded, Diesel, Super & Gas

Fuels make our lives so much easier by meeting our energy requirements. They provide power for industries, heat our homes, and run various modes of transportation. 

There are several types of fuels. They differ from each other in composition, efficiency, and application. Let’s look at the commonly used fuels in the automotive industry and see how they compare with each other.


The demand for diesel fuel remains high in many countries, and this is due to its efficiency and high energy density. It powers trucks, buses, locomotives, heavy equipment, farm machinery, electric generators, military tanks and trucks, and the majority of SUVs and MPVs. 

Let’s have a look at some defining features of this fuel. 


Diesel has a density of 0.84g/cc, meaning it punches more power or energy per volume than other low-density fuels. Also, it is more substantial and more viscous than other fuels, which indicates that it is an excellent lubricant and does not evaporate quickly. Higher viscosity means better control during fuel injection, which in turn leads to better ignition and efficiency. 

Cetane Number

The Cetane number (CN) of the fuel you’re getting is a measure of its combusting property. Diesel with a high CN burns faster in the combustion chamber, which makes it an excellent fuel. The higher its CN, the less time it takes to ignite and start combustion. Pay attention to the cetane rating required for your vehicle as specified by the manufacturer and the standards imposed in your country. 

In Australia, the Fuel Quality Standards Regulations (2001) requires that the cetane index of diesel fuels sold in the country should be at least 46. 


Diesel engines produce lower levels of carbon monoxide (CO), carbon dioxide (CO2), and hydrocarbons than petrol engines do. However, they release high levels of nitrogen oxides (NOx) and particulate matter (PM). These emissions are hazardous to health and the environment. 


Since diesel is less volatile than petrol, it is easier to refine and obtain from crude oil. Most states impose low taxes on this fuel type due to its low CO2 emissions. These two factors make diesel cheaper to procure and retail. 

Unleaded Petrol

Tetraethyl lead is a petrol additive that reduces knocking and improves the burning quality of the fuel. However, since lead is toxic, more and more countries have phased it out and replaced it with unleaded petrol. Meanwhile, in countries that have not prohibited leaded petrol yet, both leaded and unleaded versions are sold alongside each other.

Petrol is primarily used in passenger cars and light motor vehicles, such as motorbikes and scooters. They are also used to fuel petrol variants of trucks, motorboats, and other transport vehicles.

Weight, Viscosity & Lubricity

Petrol has a density of 0.73g/cc, which means that it is lighter, less viscous, and has lower lubricity than diesel. This low lubricating property increases friction in the internal components of petrol engines.

Octane Number and Rating

Octane number (ON) is to petrol, as cetane number is to diesel. Both ratings indicate fuel quality. Fuels with high ON have high compressibility, which is a quality preferred for petrol. The higher is its ON, the higher compression levels it can withstand before combustion occurs. In other words, high-ON petrol will have the ability to resist relatively high compression and temperature and will not ignite prematurely.

There are various ways to express octane number, but for motorists, it would suffice to know about the RON (research octane number). In layman’s terms, it is the octane rating obtained in a test under simulated conditions. What’s more important, the RON is the number that you will find on the petrol pumps in your local filling stations. 

Per Australia’s environmental standards, unleaded petrol (ULP) must have a minimum RON of 91 and premium unleaded petrol (PULP) not less than 95. Thus, you will find the numbers 91 and 95 labelled on refilling pumps.


Petrol engines emit higher levels of CO, NOx, and SO2. Since petrol engines consume more fuel, they emit more gases. They also tend to emit higher levels of CO2, but a lower amount of fine particles than petrol engines do. 


Due to the high costs of refining and distilling petrol, it is costlier to produce than diesel. Thus, it is generally more expensive than diesel fuel. The opposite is exact in Australia, though, where diesel is more expensive than petrol.  

Super Petrol

Super Petrol or 98RON is a type of petrol with an octane rating of 98. It’s the third number on petrol pumps aside the 91 and 95 labels. Petrol companies market them under various names, including BP Ultimate Unleaded, Super Plus Unleaded, and Shell V-Power.

This fuel is not your regular or premium unleaded petrol because it contains formulations of detergents and cleaning agents. Its claims include reduction of emissions and protection of the engine’s fuel injector and inner workings.  


Compressed Natural Gas (CNG) derives from naturally-occurring methane. It is stored in compressed cylinders to power automobile engines. Engines using CNG can achieve an efficiency of up to 50%. These are cleaner as they have lower emission levels.

Liquefied Petroleum Gas (LPG), on the other hand, is a compressed mixture of propane and butane. They burn hotter than most of the other different fuels and, hence, are a perfect choice for cooking applications. LPG, called autogas when used to run vehicles, is a by-product of crude oil refinery and natural gas extraction operations. 

The good thing about LPG is that it burns cleaner than traditional fossil fuels due to its lower carbon level. It is storable in tanks as a pressurised liquid. On the downside, issues about lower mileage and the possible buildup of precipitates dampen its acceptance as a mainstream fuel for automobiles. 

Fuels of the future

Diesel and petrol are fossil fuels, and as such, are non-renewable. While the gases are also fossil fuels, they’re the cleaner form. However, diesel and petrol remain to be the widely-used energy source for automobiles, and their emissions impact the planet significantly. 

If we want to mitigate these harmful effects, we must tap clean and renewable energy sources soon. To this end, governments and the automotive industry across the globe are looking into alternatives like hydrogen fuel, solar energy, and wind power, and especially into electricity for powering the cars of the future.