well, here in south ontario, the pump does not advertise the price of premium, motorist will have to pull into the pump station to find out the price. the spread is $.12-.15 per litre.
as for reason of spread, did pump drop the price on regular octane since more low octane were refine by SHALE sourced oil? or they only raise the price on high octane fuel? i think it's all about marketing; they don't sell at any price they want, but they sell at the price market can bear. unfortunately, gasoline is a life essential just like water and electricity in North America, so i guess they can charge anyway they want. what can we do if the pump showing $2/L or $6/Gallon? nothing really, and we can not build stash like motor oil...