[throwaway5752]

That's incorrect. Refineries have crackers (catalytic cracking units) that can be used to tune the yield. It varies seasonably at the same refinery.

From your own citation:

"Separation processes, such as distillation, dewaxing, and deasphalting make use of the differences in the physical properties of crude oil components to separate groups of hydrocarbon compounds or inorganic impurities, whereas conversion processes cause chemical changes in the hydrocarbon composition of crude oils. For example, Fluid Catalytic Cracking process breaks chemical bonds in long-chain alkanes to produce shorter chain alkanes to produce gasoline from higher boiling gas oil fractions"