[Chris B.]

I really haven't noticed a signifigant difference in gas mileage or how the car runs with between any major brand 91 octane or 93 octane. I've even done track days with Wawa 91 or 92 octane gasoline and had no issues. My 2008 Mustang GT was dynoed with 10% ethanol gasoline from the local Giant grocery store and it made good power for the mods it had.

Originally Posted by PAFirefighter11

I've designed oil refinery processes for 20 years and there is a big difference. Any of the major brands like Shell, Exxon, BP, or Chevron are OK. Some of the off brands are OK and some are not, but I would never put any of the secondary brands in my car.

There is very little difference in the major brands apart from the additives that are blended in. The vast majority of gas is transported from the refinery to local distribution points via pipelines. In several areas of the country several refiners will use a common pipeline to transport their products to remote storage facilities. So brands such as shell, BP, exxon, etc are mixed in the pipeline. There are agreements as to the quality of the gas that goes into these common lines. If Chevron ,for example, puts a 100 gallons of fuel in the pipeline from the refinery at Pascagoula, MS they are entitled to remove a 100 gallons from a distribution point in Sioux City, IA even though their fuel never went to Iowa. So even if you buy shell gas it may have been made by Chevron. The company specific additives are added at the remote distribution points and is the only thing different between major brands.

These distribution agreements are why it is possible for shell (or any other refiner) to sell fuel in places where it would otherwise be uneconomical because of transportation costs.

Most (but not all) of the secondary refiners are not part of this distribution agreement because their fuel does not meet the quality standards.

I've heard the same things from other people that work in the petroleum industry currenly. Basically all the retailer custom additives are added after it comes out of the pipeline. Its all the same grade going in and each refinery doesn't deliver directly to the local distribution points. Your Sunoco 93 might have been made by BP or Valero, but have SUnoco's additives added to it.

Originally Posted by 420sx

Can you still get gas without 10% ethanol? I feel like Im getting ripped off every time I see that.

In the winter its hard to find, but in the summer in the northeast some stations have it. Some even advertise it being Ethanol free and charge a few cents per gallon more for it.

Also http://pure-gas.org/ tries to maintain a list of Ethanol free stations.

Originally Posted by DaBombDiggidy

ethanol hurts gas mileage by about 2-4%

Real world testing on may cars shows a gas mileage drop of 5-15% using 10% ethanol. The issue is the best air/fuel ratio for 10% Ethanol gasoline is different than the best air/fuel ratio for 100% gasoline.