Gas in Montreal

We filled up our car to the brim before we left Salem (NH) on Friday morning. We figured it would take about a full tank of gas to get to Montreal. The price in Salem on that morning was about $3.25. As we drove further and further north, the price got higher and higher. Right before the border but still in Vermont it was about $3.68. The first gas station we saw after entering Montreal was an Esso station and the price was advertised at $1.27!!!! I couldn't believe my eyes! I was practically jumping up and down in the car, so excited to see such a great price and vowing that we would fill the car to the brim before leaving Canada. When we got to our B and B we asked our host Ken why the cost of gas was so cheap. "Cheap?" he says in astonishment. When I tell him we saw gas for $1.27, he says "That is for one LITER!" There are FIVE liters in a gallon! You do the math.