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All the gasoline is the same, octane is controlled by a very small amount of additives added at the end.

Midgrade (90 octane) and Premium (93-94 octane) are not higher quality gasolines, they are the same gasoline with slightly more additives.

It is a major scam how much gas stations charge per gallon for some micrograms of ignition retarders and detergents.

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No - higher octane fuels come from the refinery as higher octane - usually because the mix of blending stocks are different and you have to add in some elements to the mix that could have been used to take more lower cost product into "regular" spec.

What happens in pipelines is a lot of the same stuff goes into the pipeline aka "one big slug" at the same time. In between slugs stuff gets mixed and that becomes transmix which gets bought and sold (at a discount) and usually reprocessed and reused. Pipeline scheduling is done to reduce transmix - if high grade gasoline is next to low grade gasoline the transmix could potentially be sold as low grade gasoline.

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