Difference Between 87 and 91 Octane Gas

Gasoline or Petrol is a flammable liquid that is a transparent liquid derived from petroleum and is used as a fuel in an internal combustion engine. Various types of organic compounds are enhanced with different kinds of additives and go through the p[rocess of fractional distillation of petroleum. Gasoline can sometimes leak into the environment either in the form of a vapour or in liquid. Octane number is given to the various kinds of fuel which can withstand the compression in the internal combustion engine.

87 vs 91 Octane Gas

The main difference between 87 and 91 Octane Gas is that 87 Octane Gas is a Regular Gasoline. 91 Octane Gas is a premium Gasoline. 87 Octane Gas is a cost-effective fuel. While 91 Octane Gas is very costlier because it is better than 87 Octane Gas. 87 Octane can be used in any type of vehicle. Whereas 91 Octane can be used in only premium vehicles like sports cars etc. 91 octane has a higher octane rating, and it burns faster than 87 Octane.

87 and 91 Octane Gas

87 Octane Gas is regular gasoline that has the lowest octane level. The additive is added to the 87 octane gas so that it can become more resistant before it detonates. Regular gasoline is a normal fuel, and it is cost-effective. The efficiency of 87 octanes is very much lower compared to mid-term and premium gasoline. It is more prone to detonation because 87 octane gas can ignite at a lower temperature than other gasoline. The amount of power given by the regular gas is less. It also has more knocking and pinging than 91 octane gas.

91 Octane Gas is a premium gas. It has a higher octane rating. This type of octane is better than Regular and midgrade gasoline. It consists of 91% of iso-octane and 9% of n-heptane. Higher the number of iso-octane, anti-knocking tendency will increase. If the number of iso-octane is more, then the compression ratio will increase. So the chances of knocking will decrease. It has a higher ignition and combustion rate. It is more fine and unleaded. It doesn’t detonate easily as it can be compressed by more than 87 octanes.

Comparison Table Between 87 Octane and 91 Octane Gas

Parameters of Comparison87 Octane Gas 91 Octane Gas
Octane RatingLowHigh
IgnitionKnockingBetter and higher capability
Properties87% iso-octane & 13% n-heptane91% iso-octane & 9% n-heptane

What is 87 Octane Gas?

Octane Number or rating is given to the different types of fuel, and it is used as a standard measure to withstand the compression in the high-pressure in an internal combustion engine before it detonates. 87 Octane is a Regular gas. It is the most common type of gasoline that is used worldwide. This is also used as a Research Octane Number (RON). Regular gas is called that gas that is normal and given the rating of 87.

87 Octane has a regular performance and low efficiency than 91 octanes. If the octane rating is lower, then there will be pre-detonation. If it detonates easily, then the chances are that it can harm the performance of the vehicle. The amount of power given by 87 octanes is less than 91 octane. It cannot be compressed too much like 91. Otherwise, it will get leaked. It all depends upon the design of the engine and which Octane gas is good for your vehicle.

The properties of 87 octanes include 87% of iso-octane and 13% of n-heptane. Octane means that it is a colourless gas with the smell of gasoline. It is less dense than the water. Additives are also added to 87 Octane to make it more gas resistant. This process is commonly called pinging or knocking.

What is 91 Octane Gas?

Octane is measured by an octane testing engine. Octanes are usually formed by combining heptane and iso-octane. 91 Octane gas consist of 91% of iso-octane and 9% n-heptane. Octanes are called Primary Reference Fuels. Knocking properties are also checked in the testing engine. Additives are added in 91 octane gas to make it more resistive. It has anti-knocking properties. It has the highest octane rating. 91 Octane Gas is categorised as the Premium fuel and considered best.

It cannot be used in any type of vehicle. As it is premium gasoline, it has finer particles and is considered more clean and pure than the rest of the octane gases. The price of 91 Octane Gas is higher. It is mostly used in sports cars or premium cars. The capability of 91 Octane is better and higher than 87 Octane Gas. It can be compressed more and more than other octane gas. Because of more compression, it gives more torque to the engine.

91 Octane has a higher ignition, and it burns slower. Its efficiency and the amount of power is also higher. If a vehicle is detonating more, then it can change to 91 Octane gas. Changing fuel to 91 Octane gas doesn’t at all means that your vehicle and its engine can start giving high performance automatically. It all depends upon the design and the nature of the engine.

Main Differences Between 87 Octane and 91 Octane Gas

  1. 87 Octane Gas has a lower rating and is also called Regular Fuel. 91 Octane Gas has a higher octane rating and is also called Premium Fuel.
  2. 87 Octane is a cost-effective fuel. 91 Octane is costlier.
  3. 97 Octane has a lower ignition resulting in Pinging or Knocking. 91 Octane has a better ignition and higher capability.
  4. 87 Octane burns faster. 91Octane burns slowly.
  5. The Compression rate of 87 Octane is lower. The compression rate of 91 Octane is higher.
  6. Properties of 87 octane are 87% iso-octane & 13% n-heptane. Properties of 91 Octane are 91% iso-octane & 9% n-heptane.
  7. The efficiency of 87 Octane is lower. The efficiency of 91 Octane is higher.


Both 87 Octane and 91 Octane gases contain different types of additives. Both are given octane ratings based on their compression ratio in an internal combustion engine. 87 Octane is a more common type of gasoline used. 91 Octane is used only for specific vehicles.

Whenever a user is purchasing a vehicle, he should carefully check that which type of fuel or gasoline is more suited to their vehicle. Premium or 91 Octane cannot be used in any type of vehicle. It doesn’t mean that it will increase the performance of a vehicle automatically. Using an 87 octane rating in a vehicle may sometimes cause problems to the engine. Using a higher octane rating can increase its speed and efficiency.


  1. https://www.sciencedirect.com/science/article/pii/S0048969702002711
  2. https://www.tandfonline.com/doi/abs/10.1080/10916466.2015.1050506
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