Just got back from a 2 week road trip. 2002 Ford Taurus 24 valve. Total trip was 2633 miles, or 4237km. Total fuel consumption was 94.7 imp gallons, 113.73 US Gallons, or 430.55 Litres. That comes out to 27.8mpg imperial, 23.15mpg US or 10.16 l/100km.
Now for the interesting part.
Years ago, driving a Toyota Tercel, I found I got almost 20% better fuel mileage running US gas than running Canadian gas. No explanation why. Then on a trip to the east coast a few years ago with my 2002 PT cruiser, I got as much as 37MPG (imp) on US gas running through the mountains of vermont and across the finger lakes district, while I could not get 28MPG running from toronto to prince edward island.
On THIS trip, the forst 2501km or 1554 miles were in the US - the first 588km on my initial canadian fillup - and the average fuel economy was 31.048mpg (imperial). The last 1079 miles, or 1736km, was in Canada where my mileage was only a paultry 24.162 mpg (imperial).
My driving did not change significantly - if anything slightly slower in Canada.
Trip was Kitchener Ont to Sturgis Michigan, some short trips between sturgis, Shipshewana Ind and South Bend Ind,then on through Chicago and Millwaukee to Cascade Wisconsin, 2 round trips to OshKosh, then on through Wisconsin Dells to Michigan UP and Sault St Marie with an excursion to Sault St Marie Ont and back, then up to Sault St Marie Ontario, to Pancake Bay and WAWA, then up to Hearst Ontario, down to North Bay, and then back to Kitchener. Average highway speed in the USA was about 65 mph+, and in Canada closer to 60 .
Not only do we pay SIGNIFICANTLY more for our gas in Canada, but it appears we are buying an inferiour product as well.