High-octane fuel isn’t for every engine.
Some engines need it – but others do not.
Millions of other engines.
Feeding those engines high-octane fuel is a money-waster. High-octane “premium” fuel (which isn’t necessarily of higher quality, just higher octane; more about this in a moment) generally costs about 30-50 cents or more per gallon. If your car’s engine doesn’t require it, you’re spending several dollars more for every tankful – which can amount to several hundred dollars annually – and several thousand dollars over the 10-15 year lifespan of a new car. 
It’s also a power and mileage waster in cars that don’t need it. Many people do not grok this, but an engine not designed to burn high-octane fuel actually runs better (more efficiently) on lower octane fuel.
Because the fuel burns at the right moment. Not too soon – or too late.
That’s all octane is, really. A measure of a given fuel’s tendency to combust when subjected to increasing heat and pressure.
Some engines – generally, high-compression engines (this includes turbocharged and supercharged engines) – need a fuel that won’t burn too soon, as the result of high pressure and heat inside the engine’s cylinders – before the spark plug fires.
Which will resist combustion until the piston’s at just the right point in its travel – and not until the ignition system fires the spark plug.
High octane fuel fits that bill.
Other engines don’t have high cylinder pressure (comparatively) and so don’t need high-octane gas that is more resistant to spontaneously combusting due to high heat/pressure. They need fuel that burns more readily at lower pressures/heat.
Lower octane gas fits that bill.
This is why there is currently the option to choose the fuel with the right octane rating for your particular car’s engine. High-octane “premium” – generally, unleaded gasoline with an octane rating of 90 or more. And “regular” – generally, unleaded gasoline with an octane rating of 87 or so.
What if that choice were taken away? What if you had to pump the wrong octane fuel into your car’s tank?
Were effectively forced to pay extra for the fuel – as well down the road, in the form of lower mileage?
Read more at EricPetersAutos.com
