[Sirfoil]

The gas is the same when it arrives to the station, the only thing that changes the octane is the additive they put in after they fill the storage tank up.

Other than the "gallon" (not sure of the exact amount) of additive/detergent they add at the station it's the same gas coming from the same place delivered by the same truck weather is be Arco, Costco, or Chevron. It's all the same.

I learned this from talking to gas delivery trucker, he was at a mom and pop station at the time and his next delivery was to a shell station. He showed me the additive when I asked what octane he was carrying and said this is what changes the octane. Also by being behind a delivery truck that just finished filling up Safeway and watched him stop at Chevron.

So maybe they got the incorrect mixture at the Arco and you had too high of an octane and it was not burning or maybe Costco give you a lower octane and it burns better.

Remember the higher the octane the harder it is to ignite.