First of all, I need to mention that I'm from central Iowa, which is important to note because Iowa has a subsidy on ethanol, which makes our super unleaded gas (89 octane) roughly 10 cents cheaper than regular gas (87 octane).

Alright, so I understand octane ratings, but here is where I'm a bit confused. Nearly all of the gas stations in the area have this set up: 87-regular, 89-super unleaded, 91-premium unleaded with a rare occurence of 93.

Now, when if I were to stop at Murphy USA, which is like a Wal-Mart partnered gas station, then they have theirs set up as 89-regular, 91-super unleaded, 93-premium. However, the prices for their regular, super, and premium matches everyone else prices.

Is their fuel just a lower quality? I wouldn't think they could misadvertise the octane level. For instance, high-compression/supercharged engines require premium unleaded - or something 91 and up - yet, according to Walmart (or Murphy USA I should say) their super unleaded is really what everyone else considers premium and is also a cheaper price.

Am I missing something here? I mean, if I went there I'd just fill it with 93 to be on the safe side, but could I really be safe using their super unleaded? I usually just fill up at the BP down the road, but it's always been a curiousity of mine.