| In addition to the octane value of the fuel, the additives/quality also has a bearing on the fuel consumption. The more expensive brands do seem to have better MPG.
Some years ago I (long term) compared Jet (a UK cheapo brand) with Shell, it was just about 10 percent worse in economy. I would think that supermarket fuel would fall in the same category, providing it hasn't wrecked the engine in the meantime. |