Not too very long ago [10 years?], gasoline sold by the name brand stations here in the Southeast, had a $0.10 per gallon cost increase for each higher grade of gasoline. This had been the practice for years.
Keep in mind that the different octane gasoline sold at the pump is accomplished by blending, either at the refinery, the distribution point or at the station.
For example, 87 octane was $2.50, 89 octane was $2.60
[+4%] and premium was $2.70
[+3.8%]per gallon. I will highlight in bold the approximate percentage increase.
When gasoline prices neared the $4 mark, the difference between each grade increased to $0.25. The blending was still the same.
When prices peaked, 87 octane was @ $4.25, 89 octane was $4.50
[+5.9%] and premium was $4.75
[+5.6%].
When the gasoline prices fell back to the currently lower prices, the grade level increases
remained at +$0.25. Keep in mind, the blending practices are still the same.
Currently, 87 octane is $2.12, 89 octane is $2.37
[+11.8%] and premium is $2.62
[+10.5%] per gallon.
Just thinking.