I was looking through gas mileage discussions and since we are an international group sometimes you could get confused. Basically the Imperial gallon has forty Imperial ounces which are ever so slightly less than the US ounce. So, the difference is close to a US quart per gallon. This even is reflected in what we call 55 gallon drums. They are 44 gallons in the Imperial. Thank God for the Imperial pint. That's a decent pour.