People that say fuel is the same at every gas station remind me of those that say all news stations are the same and so is Insurance.
Laws control Insurance. Laws Control Fuel ratings and what the grades require.
They all have their fuel processed by the same refinery! But each has it's own "Marketing/Mixture" to meet their needs and the laws.
When it comes to gas, the brand matters only as much as the detergents and other "cleaning" agents that they use in it. Some brands such as Chevron and Shell's premium gas then to have significantly higher amount of these additives than required by law and so they advertise accordingly.
Premium gas has a higher octane rating meaning less knocking in high compression engines and high powered engines. While most modern engines prevent knocking by those new fangled computers, you do lose a small amount of power if you use a lower octane than recommended.
Do they make a difference? Yes, but only if you're using a high performance engine. Most fuels have a high enough standard that it doesn't really matter if you drive a normal car nowadays.
Now if you want to see who is "Professionally" rated to be the top tear... http://www.toptiergas.com/retailers.html
Also... One mans AM/PM is not anothers. Or 7-11 or Circle K etc. These are franchises that have requirements, but also have limitations due to locations. So not all use the same fuel (Union 76/BP/Mobil).
Engines of today are engineered with such tight tolerances it is almost impossible to go wrong with fuel. Not to mention "Most" vehicles today are designed for "World" usage in mind. And a lot of countries have lower fuel requirements/restrictions than we do in the USA and Canada.
That all said. We run Chevron. Having rebuilt a fare amount of my own engines over the years I learned two things...
- Use the factory recommended oil grade but use premium top tear brand. (And no, Pennzoil is NOT one of those in my mind. The grime was ungodly).
- Use Chevron middle grade as much as possible, or Shell if no Chevron is available.
All because of personal findings. Not from my Uncle who has been a fuel delivery driver for 30+ years, or my Cousin who is in Government, or all my mechanic buddies.
Purly based on 25+ years of capturing my fuel mileage at all times (Even rental cars) and tear downs of engines that I have either used for every day use or abuse on the weekends (Rock crawling, racing, mudding ETC).
These basic rules of thumb will help...
- If a tanker truck is filling that gas station... Move on to another station or... Wait 30 minutes. Why? Because every single fuel tank in the ground in the US does have water in it by design. And while the fuel is being added the water is being mixed into the new fuel. Let it settle and get better fuel mileage than you will with that added water % in the fuel. Keep in mind this is changing in the future as tanks get replaced, but that is a good general knowledge for now.
- If affordable, use the mid grade. After well over 2,000,000 miles of various usages and vehicle types... I find that the 89 grade with the balance between a good fuel cleaner and such is the best bang for my $. The premium grade causes lower gas mileage, and the lower grade fuel requires more maintenance to said vehicle. So look at it like this. Premium is meant for top performance. Not gas mileage. Low grade is meant for cheap, has the most diluted mixture of solvents, and requires you (If done correctly) at every oil change to run the cleaner it lacks. And if missed or overlooked, starts to reduce your gas mileage in said vehicle as deposits do add up. The middle grade has a happy medium, good gas mileage and performance with no added maintenance needs.
- One persons altitude, road conditions, weather, vehicle type, vehicle condition, tire pressure/balance, right foot, left foot and so on and so on... Makes it impossible for one person to tell another what will work for them. It requires no less than five full tanks of gas per grade and service station to find what works best for you.