A local gas station has a “sale” a few times a week. Normally, there prices are something like $1.39, $1.49 and $1.59 for 87, 89 & 92 octanes, respectively. However, on the “sale” days, the price is $1.39, $1.39 and $1.39.
Is it legal to markup the price of one octane while lowering the price of another?
Umm, which one is increased in price? It seems like you are saying the regular is the same price, the Mid grade is 10 cents less and the Premium is 20 cents less.
?!?
Is it legal? You can do with what you own whatever you want. You can give it away if you like. Why 'wouldn’t it be legal? I have to wonder what line of reasoning leads you to think like that. Can you explain?
Whoops. 
I meant that the prices are now $1.49, $1.49 & $1.49 for 87, 89 & 92 octanes, respectively. The regular goes up, premium goes down and midgrade stays the same.
The reason I’m wondering if its legal is because if you raise the price of the regular gas, then its not on “sale”…
Well, as a previous poster alluded to, they are a private business and can charge whatever they want to. Personally it seems like a tempest in a teakettle. Seriously, if all the grades are $1.499/Gal. who is going to get the el cheapo stuff? Even crappy cars will be happier with the mid grade.
Re: the semantics of the word “sale”, obviously the only one on sale is the Premium. The similar prices is just a marketing ploy, alliteration and all that…
So technically only one grade is on sale. I’d bet there is no sign that says ALL gas on sale, just a generic Gas Sale
It may depend upon that state’s pricing laws.
I believe there are some states (no cites - all from memory) that define a “sale” as being a lower price point than the “regular” price point in the past 30 days.
What am I saying? Here’s an example.
If a store drops the price of an item and calls it on sale, then that sale price must not have existed for that item in the previous 30 days.
If this recollection is correct, and the OP’s gas station is in that state, then they cannot call it a “sale.” Sure, they can still drop the price every week, and then have it go back up later in the week, but they cannot advertise the lower price as a sale.
Clear as mud? 
No crappy cars will only pollute more with mid grade. At least according to the FTC and the car talk guys.
Not if you live in Wisconsin at least. It is illegal for a retailer to sell gas substantially below what the market will bear (I don’t know how much lower that is). The thinking is this will prevent large companies, like Wal*Mart from opening gas stations that severly undercut the “mom and pop” stations, thereby driving out the competition.
I don’t know how the enforce it, and I don’t agree or disagree with it, but the law is still very much there.
It may be the manager is really bad at running his business, or can’t store enough of the low-grade to meet demand. Hence, the once-a-week “sale” that encourages people to buy what he had plenty of – the mid- and premium-grades.