I've been trying out fuel efficiency of different gas brands over the course of the past two months and came up with surprising results. The brand of gas DO affect your overall fuel efficiency and the old adage of "You get what you pay for" applies when choosing gas brands. Here's a snapshot of what I've discovered.
The analysis is based in and around Southern California in the Greater Los Angeles County. Gas price is subjective to the location and traffic of the location. At the bottom of the barrel is Arco branded gas. While cheapest by far compared to competing brands (usually $0.10c cheaper per gallon), it also provide the worst fuel efficiency. At best, a full tank only yielded 270 miles to the tank compared to 380 using a different brand. For the cost per gallon you perceived to have saved, you are making it up for higher frequency at the gas station. That and in addition to the $0.45 surcharge if you use your debit card. Not only do the gas of Arco burn off faster, the quality leaves room for desire. I noticed the RSX bogs and lags when accelerating - i.e. the acceleration is not as smooth, kind of like accelerating in an automatic car. The comparison is like putting 87 octane in your RSX versus 91 octane, except that 91 octane of Arco branded fuel feels no different than 87 octane!
Since Arco is the lowest quality gas in my comparative analysis, we'll use it as the base index where all the other competing brand is compared against.
Exxon-Mobil yielded better results than Arco. A full tank of highway driving gave me an average of 340-360 miles. The price per gallon of Exxon-Mobil fuel is relatively within the range of Arco, usually about $0.10-$0.15 higher than Arco.
On the upper rung of the best-MPG-for-your-buck in fuel efficiency hierarchy are Chevron and Shell. Chevron gas is usually $0.15-$0.25 higher than Arco gas. A full tank of Chevron gas yields an average of 360-370 miles. Finally, Shell appears to be the most costly, but yields the best fuel efficiency at up to 370+ miles per full tank.
Base on my finding, I would avoid Arco gas and select one of the other aforementioned brands. It's more cost efficient in the long run.