The standard light petroleum distillate for vehicle engines, "regular gasoline," is (or is equivalent to) some mix of heptane (C7) and octane (C8). Higher proportions of C8 are more knock-resistant, which allow for higher compression ratios and thus more efficient energy utilization in internal combustion engines.
Don't modern refineries produce pretty much any hydrocarbon mix they want through combinations of distillation, cracking, and alkylation?
If so, then why is "regular" gasoline produced in such quantities, and why is a premium charged for more knock-resistant ("higher octane") blends? For example, if a refinery had to produce only one light fuel distillate, couldn't it just as easily and cheaply produce a "100 octane" blend as the current "87 octane"?
Or is it actually cheaper to produce "lower octane" petrol?
Note that "100 octane" doesn't mean 100% octane, as the "octane" number of a hydrocarbon depends on its isomers, with more highly-branched isomers having more knock resistance. So 100 octane fuel can be produced with many blends of C7, C8, and even include lighter and heavier hydrocarbons.
A characterization of the isomeric constituents of crude oil might answer this question. For example, if crude feedstock tends to have more linear isomers, then energy would have to be put into isomerization to produce more knock-resistant distillates.