To make premium fuel, crude oil is essentially boled, under controlled environmental conditions, and the iso-thises and hepta-thats, that are less dense literally coagulate at different depths within the pressure vessel, where they are skimmed off.

The lighter hydrocarbon compounds are used in the manufacture of acetone-type industrial strippers and other chemicals, where they command a higher price per gallon than if they are used in boosting the octane level of the base gasoline stocks that build 87 RON.

Here's a hypothetical scenario that shows the economics of this issue, as discussed in the SCC article:

In order to make 200 million gallons of 93 RON, the refiner has to add about 500k gallons of these high-end stocks to raise the octane level of 87 RON regular fuel.
Those 500,000 gallons of high-end stocks are used at a "loss", because they would command a much higher price if they were sold off to other uses.

When the demand for premium rose, and the demand for regular began to level off, more and more high-end stocks were needed to continue producing 93 RON premium. Thus the refineries would lose more potential sales dollars of these high-end light-hydrocarbon fuel stocks to their use in the production of premium gas.

So, in response to the increased demand for premium fuel, the refineries decided to skimp on the addition of high-end fuel addition, and instead decided to lower the overall octane rating to 91 RON.

Better?

please say yes. please say yes.. it's getting late.