Sorry about the corny double meaning in the heading. I couldn't resist.

I do have a question about gas prices. Why are the different grades always exactly 10 cents apart at all the stations no matter what the gas price is?

When regular was $2.00, mid grade was $2.10 and premium was $2.20. Now gas is (about) $3.15, 3.25, and $3.35.

Shouldn't it be proportional? In other words, if mid grade costs .05 percent more when regular is $2.00 a gallon, shouldn't it cost .05 percent, or 15 cents, a gallon more when regular is $3.15 a gallon? I don't want to give anyone an excuse to charge even more for gas, so let's look at it the other way. If mid grade only costs 10 cents a gallon (a little more than .03 percent) more than regular now, shouldn't there only be a 6 cent difference when regular is $2.00 a gallon?

Furthermore, all the station owners can't be paying their suppliers exactly the same difference between the grades, and the difference in cost between the grades has to vary from one supplier to another and from one time to another, right? Is it just a custom? Is there even any difference in the gas? When regular is $20 a gallon, will premium be $20.20? (I hope that is just a joke.)