There are so many gas brands in market these days (Shell, Citgo, Sunoco, BP, Hess, Mobil, Chevron, ...) and recently a friend suggested using Mobil over Sunoco not only pushes his MPG high but he can also feel the smoothness in his driving.
Is it true that one brand is better than the other? And if so, which brands in market are better than the others?
Here in my corner of the Sunshine State, St. Petersburg, our gas comes with at least 10% Ethanol whether we want it or not. Speaking just for myself, I've found that the higher the Ethanol content, the lower the mileage in direct proportion to the percentage of Ethanol i.e. a 10% increase of Ethanol results in a 10% decrease in gas mileage.
Having said all that I've found Mobil has been the best for our vehicles: PT Cruiser, BMW Z-3, old BMW motercycle and Citgo, by far, the worst.
10% less mileage for E10 over pure gas is totally bogus. The difference is around 1-2%, and when I logged mileage of E10 vs pure gas over about 20-30 tanks of each, I found that there was a noticeable difference and that it was around 2%. There have been some reports that certain stations use more than 10% ethanol in their E10, but not the 40-50% ethanol that you would need to see a 10% drop in mileage.
Different pure gas blends all will get virtually the same mileage. The amount of additives in each are so small that they don't make much difference, and the measuring error (i.e. topping it off) is much more significant, no matter how good you think you are at topping off your tank. Gas is gas and all brands have basically the same energy content. But the additives in the good gas can keep the fuel injectors much cleaner and prevent deposits from forming in them -- which is very important in the long term. 10 to 15-year-old injectors usually have 3-5% flow disparity between them, which translates directly to smoothness and mpg as that means the richest cylinder is 3-5% richer than the leanest cylinder. However that's only an issue in the long term.
Brands like Shell and Chevron are usually the best (and most expensive) but 76/Conoco Phillips is relatively cheap and I've heard it's one of the higher quality gasolines.
I've used a few different brands with my MINI, and did notice a difference not only in MPG, but also the feel of the car, as the original poster mentions. When using Arco/Safeway, the engine felt "rougher", more prone to a "cold start stumble", which is something mentioned a lot in various MINI forums, both local and national. When moving to a Top Tier gas (http://www.toptiergas.com), I've noticed that my MPG is a little higher (heavy right foot not withstanding), and the "cold start stumble" is gone. The engine feels smoother over the entire range from first start in the morning until I pull into work, 30+ miles later.
As such, I never use the cheaper priced gas. Yes, I pay more per gallon, but that difference only equates to a couple bucks more per tank. Worth it, IMO, if it means the engine is going to last longer because I'm using a higher quality product.
It's hard to compare, the differences will be minimal. It's even harder to compare US fuel with that in Europe. The fuel in the USA is unrefined and burns "dirty" hence why the car emissions seen extortionate compared to those in Europe.
In Europe you can get fuel up to and over RON 102, where as in the US, fuel can be sold as low as RON 85. This is because the emission tests are different in both countries and it's required to burn cleaner in Europe for the strict Emission standards.
So basically, the more expensive the fuel, the higher the octane, the better your fuel consumption will be and the smoother your car will run.
FIAT500ABARTH, higher octane gas does not get better mileage except on very few (mostly high-performance) vehicles. If your car is fairly new and requires high-octane gas and you put regular in it, you may see a bit of a difference (as well as it running poorly and possibly blowing up depending on the motor), but not vice-versa. Your car is probably one of few examples of cars that require premium to run well, but won't destroy themselves if you don't.
95RON is roughly equal to crappy California premium which is 91 AKI=(RON + MON)/2. 97-98RON is about the same thing as the 92 to 94 AKI we get as premium in most other states. The cheapest gas you can buy in the US is 85 AKI (only in high-altitude states) which equals around 90-92RON. Nowhere in the US can you buy 85RON gasoline, that's ridiculous. And there are plenty of places to buy 100 or 110 AKI (105-115RON) though it's incredibly expensive, at least by US standards.
RON is an octane measurement method that tests under low temperatures and loads -- MON is the other primary measurement method and tests under high temps and loads, and hence the MON rating for a gas will be 8-10 points lower than the RON for the same gas. Since we use the average of the two (which is the anti-knock index or AKI) the 92-94AKI unleaded is pretty close to the 98 RON that is sold at the pump in Europe. They both have roughly the same octane and though I'm not sure what the differences in sulfur content are required to be, low-sulfur fuel has slightly less energy in it than regular gas, resulting in a mileage drop about the same as using E10 instead of regular gas.
You're certainly right that higher octane petrol only really helps with MPG on higher performance cars. On my car (A n/a Fiat 500) putting premium fuel in doing really seem to make any difference in terms of economy but in my wifes car which is turbocharged it makes a difference.
If you want to see bad quality fuel you should try fuel in Australia, it's just not as well refined as in Europe and IIRC the standards for quality are lower than elsewhere. Of course I could be talking crap but that's just my experience.
Many US fuels are garbage. Having a very knock prone motor (modded 6.1L Hemi), I can say without a shadow of a doubt, that Exxon Mobil and BP are the best gases available. My tuners at DiabloSport agree.
Sunoco used to be good too, but they have dropped off badly in the past year or so. The absolute worst are the so called "Top Tier" brands. Shell for instance, knocks like crazy. The whole "Top Tier" crap is just propaganda. They can keep their crap.
here is a little know fact. here in the US diesel, gas is pumped in the same pipeline one right after the other. Say they put in 1 million gallons of diesel in they measure out 1 million gallons on the other end of the pipe line. They they might do aviation gas 1 million gallons in and out then maybe gas. I don't know the specifics but you get a mix when they change. Some of the big company Shell, BP, Exxon get the fuel that is more in the middle of the said million gallons which is better quality. The stuff that is near the mixed state goes to the mom and pop stores and no name gas stations. Gas is gas and to get a higher octane they put there additives to get the octane they want. I think each company has there own additives. When the tank trucks get fuel at the tank farms they measure out what they need, heavier fuel settles to the bottom and lighter to the top. Like a black and tan beer! and they can take out from different levels. I got this info from a pipe line guy. I might not be too accurate on this but you can get the jest of what is going on. Here in Greensboro we have many big holding tanks that are hooked to the pipe line. I have heard it is better to stick to a brand but I get what I can. later