I always use Shell Optimax, or if not available, the ocassional fill with BP Ultimate.

Just came back from a longish trip where I used several filling stations for the first time. At one particular motorway Shell station the Optimax was very expensive, as is usual with all brands at motorway stations in the UK. But the performance of my 997S suddenly came to life in a big way!!

Then on next fill it reverted to what I'd previously considered to be normal. Another fill and it flew again - then next fill back to normal.

Is it possible that some stations are charging super un-leaded prices for standard un-leaded products? If so, is there any way we can prove it?