Octane is resistance, not power
The octane number of a petrol measures how well it resists igniting under compression before the spark arrives. That premature ignition is knocking, and it damages an engine.
It is not a measure of energy content, and a higher-octane fuel does not contain more of it. An engine designed for a higher octane can run a higher compression ratio and therefore make more power — but putting a high-octane fuel into an engine that was not designed for one changes very little, because the engine cannot use the resistance it is being given.
That is the honest core of it, and it is why the premium grades are worth it in some vehicles and not in others rather than being universally better.
What the branded names are
Each oil marketing company sells its higher-octane petrol under its own brand name, and they are broadly comparable products rather than different categories. Your fuel-type register should carry whatever your company supplies you, under the name your customers ask for.
Cetane is the opposite property
For diesel the useful number is cetane, and it measures roughly the reverse: how readily the fuel ignites under compression. A diesel engine has no spark, so ignition delay is the thing that matters, and a higher cetane number means a shorter delay — generally smoother running and easier starting.
Premium diesels are typically sold on a combination of higher cetane and an additive package rather than on cetane alone.
The additive package is most of the difference
Beyond the octane or cetane number, what separates a branded premium grade from the regular one is usually a detergent and friction-modifier package intended to keep injectors and valves clean over time.
Those are long-run claims about engine condition rather than immediate ones about performance, which makes them genuinely hard for a customer — or a dealer — to verify from the forecourt. Selling them honestly means describing them as what they are.
What an extra grade costs you operationally
This is the part nobody explains to a dealer, and it is the reason an extra grade is a business decision rather than a menu addition.
- Another tank, or a share of one. A grade needs its own tank — you cannot store two grades in one and expect either to be what it says.
- Another reconciliation. Every tank carries its own daily dip, its own book stock and its own variance. Three grades is three registers, not one with an extra column.
- More dead stock. Each tank keeps fuel below the suction line that cannot be sold, so an extra tank is an extra permanent chunk of working capital sitting in the ground.
- Slower turnover on the premium tank. A grade that sells slowly sits longer, and long-standing stock is more exposed to whatever your tank's condition does to it.
One register per tank, whatever the grade
The temptation with a premium grade is to fold it into the petrol line because the volumes are small. That is the same mistake as pooling two tanks of the same fuel — a low-volume tank drifting is easy to hide inside a high-volume one, and the small tank is the one most likely to be neglected.
Keeping the grades straight in your records
Configure your fuel types once and attach each tank to exactly one of them, and each nozzle to exactly one tank. That chain is what keeps a grade's litres attributable all the way from the dispenser to the fuel-wise report, and it is what meter readings are built on.
The stock register format is per tank for this reason, and the free register template has a sheet per tank rather than a column per fuel.
Frequently asked questions
Is premium petrol worth it for the customer?
It depends on the vehicle. An engine designed for a higher octane can use the extra knock resistance; one that is not designed for it largely cannot, and the additive package is a long-run claim about engine condition rather than an immediate one about performance. Manufacturers state a recommended fuel, and that is the honest answer to give a customer who asks.
Can I store two grades in one tank?
No. Whatever comes out will be neither of them, your stock records for both become meaningless, and you are selling something other than what the customer asked for. A grade needs its own tank.
Does a premium grade earn a better margin?
Dealer commission is set per litre by the oil marketing company and differs by product, so take yours from your own purchase and selling prices. What is certain is that the extra tank, the extra dead stock and the extra reconciliation are real costs, and a grade that sells slowly may not cover them.
How do I add a new grade to my records?
Add the fuel type, add the tank with its capacity, attach its nozzles, and start a separate register for it from day one. Retrofitting a grade into records that pooled it is far harder than separating it at the start.