In general, it does not matter what type of gas one uses in a car. Most cars are built to run on economy gas, and giving them higher octane fuel is rather like giving a treat to an overstuffed dog. It’s not necessary, it provides no additional benefits, and it will cost more.

However, some people believe that what kind of gas is used, rather than octane measurements, seem to make a difference in car performance. This can generally be attributed not to the gas but to types of additives in the gas. Thus for some people, there can be a difference between one company’s brand and another company’s brand. For many, this makes no difference either.

Some cars do require higher octane gas. In general an owner’s manual will inform one of this fact. For example, if a car has a high compression engine, as do many luxury or sports car, they may require an octane rating that is higher. This is the case with cars like Porsches or Jaguars.

Generally, the purpose of higher octane gas is to prevent knocking or pinging in the engine, and to increase performance. Occasionally a very loud knocking can damage the engine. Knocking sounds are caused by the sudden ignition of fuel, which occurs almost instantaneously. The sound reverberates throughout the cylinder causing an audible ping or knock sound.

If you can eliminate knock by using higher octane gas, then it may be worth the extra money to do so. Though minor knock is unlikely to damage a car, consistent and loud knocking can. So occasionally one has to ignore the manufacturer’s instructions and dig deep for the high performance gas.

There is a very important distinction between using gas and diesel. Diesel fuel cars will die on gasoline, and the process of cleaning out regular gas in a diesel engine can be highly expensive. If you own a diesel car, do not use regular gas of any kind. Only use diesel fuel, commonly available at most filling stations.